Cetacea

Cetaceans (from , from , sea monster) are aquatic mammals constituting the infraorder Cetacea (). Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively carnivorous diet. They propel themselves through the water with powerful up-and-down movement of their tail which ends in a paddle-like fluke, using their flipper-shaped forelimbs to maneuver.
While the majority of Cetaceans live in marine environments, a small number exclusively reside in brackish water or freshwater. Having a cosmopolitan distribution, they can be found in some rivers and all of earth's oceans and many species inhabit vast ranges where they migrate with the changing of the seasons.
Cetaceans are famous for their high intelligence and complex social behaviour as well as the enormous size of some of its members, like the blue whale reaching a maximum confirmed length of 29.9 meters (98 feet) and weight of 173 tonnes (190 short tons), making it the largest animal known to have ever existed.
There are approximately 86 living species split into two parvorders: Odontoceti or toothed whales (containing porpoises, dolphins, other predatory whales like the beluga and the sperm whale, and the poorly understood beaked whales) and the filter feeding Mysticeti or baleen whales (which includes species like the blue whale, the humpback whale and the bowhead whale).
Cetaceans have been extensively hunted for their meat, blubber and oil by both indigenous peoples and commercial operations. Although the International Whaling Commission has agreed on putting a halt to commercial whaling, some nations continue to do so. They also face environmental hazards such as underwater noise pollution, plastic buildup and ongoing climate change, but how much they were affected varies widely from species to species, from minimally in the case of the southern bottlenose whale to the baiji (or Chinese river dolphin) which is considered to be functionally extinct due to human activity.
Baleen whales and toothed whales.
The two parvorders, baleen whales (Mysticeti) and toothed whales (Odontoceti), are thought to have diverged around thirty-four million years ago.
Baleen whales have bristles made of keratin instead of teeth. The bristles filter krill and other small invertebrates from seawater. Grey whales feed on bottom-dwelling mollusks. Rorqual family (balaenopterids) use throat pleats to expand their mouths to take in food and sieve out the water. Balaenids (right whales and bowhead whales) have massive heads that can make up 40% of their body mass. Most mysticetes prefer the food-rich colder waters of the Northern and Southern Hemispheres, migrating to the Equator to give birth. During this process, they are capable of fasting for several months, relying on their fat reserves.
The parvorder of Odontocetes – the toothed whales – include sperm whales, beaked whales, killer whales, dolphins and porpoises. Generally the teeth are designed for catching fish, squid or other marine invertebrates, not for chewing them, so prey is swallowed whole. Teeth are shaped like cones (dolphins and sperm whales), spades (porpoises), pegs (belugas), tusks (narwhals) or variable (beaked whale males). Female beaked whales' teeth are hidden in the gums and are not visible, and most male beaked whales have only two short tusks. Narwhals have vestigial teeth other than their tusk, which is present on males and 15% of females and has millions of nerves to sense water temperature, pressure and salinity. A few toothed whales, such as some killer whales, feed on mammals, such as pinnipeds and other whales.
Toothed whales have well-developed senses – their eyesight and hearing are adapted for both air and water, and they have advanced sonar capabilities using their melon. Their hearing is so well-adapted for both air and water that some blind specimens can survive. Some species, such as sperm whales, are well adapted for diving to great depths. Several species of toothed whales show sexual dimorphism, in which the males differ from the females, usually for purposes of sexual display or aggression.
Anatomy.
Cetacean bodies are generally similar to that of fish, which can be attributed to their lifestyle and the habitat conditions. Their body is well-adapted to their habitat, although they share essential characteristics with other higher mammals (Eutheria).
They have a streamlined shape, and their forelimbs are flippers. Almost all have a dorsal fin on their backs that can take on many forms depending on the species. A few species, such as the beluga whale, lack them. Both the flipper and the fin are for stabilization and steering in the water.
The male genitals and mammary glands of females are sunken into the body.
The body is wrapped in a thick layer of fat, known as blubber, used for thermal insulation and gives cetaceans their smooth, streamlined body shape. In larger species, it can reach a thickness up to half a meter (1.6 ft).
Sexual dimorphism evolved in many toothed whales. Sperm whales, narwhals, many members of the beaked whale family, several species of the porpoise family, killer whales, pilot whales, eastern spinner dolphins and northern right whale dolphins show this characteristic. Males in these species developed external features absent in females that are advantageous in combat or display. For example, male sperm whales are up to 63% percent larger than females, and many beaked whales possess tusks used in competition among males.
Hind legs are not present in cetaceans, nor are any other external body attachments such as a pinna and hair.
Head.
Whales have an elongated head, especially baleen whales, due to the wide overhanging jaw. Bowhead whale plates can be long. Their nostril(s) make up the blowhole, with one in toothed whales and two in baleen whales.
The nostrils are located on top of the head above the eyes so that the rest of the body can remain submerged while surfacing for air. The back of the skull is significantly shortened and deformed. By shifting the nostrils to the top of the head, the nasal passages extend perpendicularly through the skull. The teeth or baleen in the upper jaw sit exclusively on the maxilla. The braincase is concentrated through the nasal passage to the front and is correspondingly higher, with individual cranial bones that overlap.
In toothed whales, connective tissue exists in the melon as a head buckle. This is filled with air sacs and fat that aid in buoyancy and biosonar. The sperm whale has a particularly pronounced melon; this is called the spermaceti organ and contains the eponymous spermaceti, hence the name "sperm whale". Even the long tusk of the narwhal is a vice-formed tooth. In many toothed whales, the depression in their skull is due to the formation of a large melon and multiple, asymmetric air bags.
River dolphins, unlike most other cetaceans, can turn their head 90°. Most other cetaceans have fused neck vertebrae and are unable to turn their head at all.
The baleen of baleen whales consists of long, fibrous strands of keratin. Located in place of the teeth, it has the appearance of a huge fringe and is used to sieve the water for plankton and krill.
Brain.
The neocortex of many cetaceans is home to elongated spindle neurons that, prior to 2019, were known only in hominids. In humans, these cells are thought to be involved in social conduct, emotions, judgment and theory of mind. Cetacean spindle neurons are found in areas of the brain homologous to where they are found in humans, suggesting they perform a similar function.
Brain size was previously considered a major indicator of intelligence. Since most of the brain is used for maintaining bodily functions, greater ratios of brain to body mass may increase the amount of brain mass available for cognitive tasks. Allometric analysis indicates that mammalian brain size scales at approximately two-thirds or three-quarter exponent of the body mass. Comparison of a particular animal's brain size with the expected brain size based on such an analysis provides an encephalization quotient that can be used as an indication of animal intelligence. Sperm whales have the largest brain mass of any animal on earth, averaging and in mature males. The brain to body mass ratio in some odontocetes, such as belugas and narwhals, is second only to humans. In some whales, however, it is less than half that of humans: 0.9% versus 2.1%.
Skeleton.
The cetacean skeleton is largely made up of cortical bone, which stabilizes the animal in the water. For this reason, the usual terrestrial compact bones, which are finely woven cancellous bone, are replaced with lighter and more elastic material. In many places, bone elements are replaced by cartilage and even fat, thereby improving their hydrostatic qualities. The ear and the muzzle contain a bone shape that is exclusive to cetaceans with a high density, resembling porcelain. This conducts sound better than other bones, thus aiding biosonar.
The number of vertebrae that make up the spine varies by species, ranging from forty to ninety-three. The cervical spine, found in all mammals, consists of seven vertebrae which, however, are reduced or fused. This fusion provides stability during swimming at the expense of mobility. The fins are carried by the thoracic vertebrae, ranging from nine to seventeen individual vertebrae. The sternum is cartilaginous. The last two to three pairs of ribs are not connected and hang freely in the body wall. The stable lumbar and tail include the other vertebrae. Below the caudal vertebrae is the chevron bone.
The front limbs are paddle-shaped with shortened arms and elongated finger bones, to support movement. They are connected by cartilage. The second and third fingers display a proliferation of the finger members, a so-called hyperphalangy. The shoulder joint is the only functional joint in all cetaceans except for the Amazon river dolphin. The collarbone is completely absent.
Fluke.
They have a cartilaginous fluke at the end of their tails that is used for propulsion. The fluke is set horizontally on the body, unlike fish, which have vertical tails.
Physiology.
Circulation.
Cetaceans have powerful hearts. Blood oxygen is distributed effectively throughout the body. They are warm-blooded, i.e., they hold a nearly constant body temperature.
Respiration.
Cetaceans have lungs, meaning they breathe air. An individual can last without a breath from a few minutes to over two hours depending on the species. Cetacea are deliberate breathers who must be awake to inhale and exhale. When stale air, warmed from the lungs, is exhaled, it condenses as it meets colder external air. As with a terrestrial mammal breathing out on a cold day, a small cloud of 'steam' appears. This is called the 'spout' and varies across species in shape, angle and height. Species can be identified at a distance using this characteristic.
The structure of the respiratory and circulatory systems is of particular importance for the life of marine mammals. The oxygen balance is effective. Each breath can replace up to 90% of the total lung volume. For land mammals, in comparison, this value is usually about 15%. During inhalation, about twice as much oxygen is absorbed by the lung tissue as in a land mammal. As with all mammals, the oxygen is stored in the blood and the lungs, but in cetaceans, it is also stored in various tissues, mainly in the muscles. The muscle pigment, myoglobin, provides an effective bond. This additional oxygen storage is vital for deep diving, since beyond a depth around , the lung tissue is almost completely compressed by the water pressure.
Organs.
The stomach consists of three chambers. The first region is formed by a loose gland and a muscular forestomach (missing in beaked whales), which is then followed by the main stomach and the pylorus. Both are equipped with glands to help digestion. A bowel adjoins the stomachs, whose individual sections can only be distinguished histologically. The liver is large and separate from the gall bladder.
The kidneys are long and flattened. The salt concentration in cetacean blood is lower than that in seawater, requiring kidneys to excrete salt. This allows the animals to drink seawater.
Senses.
Cetacean eyes are set on the sides rather than the front of the head. This means only species with pointed 'beaks' (such as dolphins) have good binocular vision forward and downward. Tear glands secrete greasy tears, which protect the eyes from the salt in the water. The lens is almost spherical, which is most efficient at focusing the minimal light that reaches deep water. Cetaceans are known to possess excellent hearing.
At least one species, the tucuxi or Guiana dolphin, is able to use electroreception to sense prey.
Ears.
The external ear has lost the pinna (visible ear), but still retains a narrow external auditory meatus. To register sounds, instead, the posterior part of the mandible has a thin lateral wall (the pan bone) fronting a concavity that houses a fat pad. The pad passes anteriorly into the greatly enlarged mandibular foramen to reach in under the teeth and posteriorly to reach the thin lateral wall of the ectotympanic. The ectotympanic offers a reduced attachment area for the tympanic membrane. The connection between this auditory complex and the rest of the skull is reduced—to a single, small cartilage in oceanic dolphins.
In odontocetes, the complex is surrounded by spongy tissue filled with air spaces, while in mysticetes, it is integrated into the skull as with land mammals. In odontocetes, the tympanic membrane (or ligament) has the shape of a folded-in umbrella that stretches from the ectotympanic ring and narrows off to the malleus (quite unlike the flat, circular membrane found in land mammals.) In mysticetes, it also forms a large protrusion (known as the "glove finger"), which stretches into the external meatus and the stapes are larger than in odontocetes. In some small sperm whales, the malleus is fused with the ectotympanic.
The ear ossicles are pachyosteosclerotic (dense and compact) and differently shaped from land mammals (other aquatic mammals, such as sirenians and earless seals, have also lost their pinnae). T semicircular canals are much smaller relative to body size than in other mammals.
The auditory bulla is separated from the skull and composed of two compact and dense bones (the periotic and tympanic) referred to as the tympanoperiotic complex. This complex is located in a cavity in the middle ear, which, in the Mysticeti, is divided by a bony projection and compressed between the exoccipital and squamosal, but in the odontoceti, is large and completely surrounds the bulla (hence called "peribullar"), which is, therefore, not connected to the skull except in physeterids. In the Odontoceti, the cavity is filled with a dense foam in which the bulla hangs suspended in five or more sets of ligaments. The pterygoid and peribullar sinuses that form the cavity tend to be more developed in shallow water and riverine species than in pelagic Mysticeti. In Odontoceti, the composite auditory structure is thought to serve as an acoustic isolator, analogous to the lamellar construction found in the temporal bone in bats.
Cetaceans use sound to communicate, using groans, moans, whistles, clicks or the 'singing' of the humpback whale.
Echolocation.
Odontoceti are generally capable of echolocation. They can discern the size, shape, surface characteristics, distance and movement of an object. They can search for, chase and catch fast-swimming prey in total darkness. Most Odontoceti can distinguish between prey and nonprey (such as humans or boats); captive Odontoceti can be trained to distinguish between, for example, balls of different sizes or shapes. Echolocation clicks also contain characteristic details unique to each animal, which may suggest that toothed whales can discern between their own click and that of others.
Mysticeti have exceptionally thin, wide basilar membranes in their cochleae without stiffening agents, making their ears adapted for processing low to infrasonic frequencies.
Chromosomes.
The initial karyotype includes a set of chromosomes from 2n = 44. They have four pairs of telocentric chromosomes (whose centromeres sit at one of the telomeres), two to four pairs of subtelocentric and one or two large pairs of submetacentric chromosomes. The remaining chromosomes are metacentric—the centromere is approximately in the middle—and are rather small. Sperm whales, beaked whales and right whales converge to a reduction in the number of chromosomes to 2n = 42.
Ecology.
Range and habitat.
Cetaceans are found in many aquatic habitats. While many marine species, such as the blue whale, the humpback whale and the killer whale, have a distribution area that includes nearly the entire ocean, some species occur only locally or in broken populations. These include the vaquita, which inhabits a small part of the Gulf of California and Hector's dolphin, which lives in some coastal waters in New Zealand. River dolphin species live exclusively in fresh water.
Many species inhabit specific latitudes, often in tropical or subtropical waters, such as Bryde's whale or Risso's dolphin. Others are found only in a specific body of water. The southern right whale dolphin and the hourglass dolphin live only in the Southern Ocean. The narwhal and the beluga live only in the Arctic Ocean. Sowerby's beaked whale and the Clymene dolphin exist only in the Atlantic and the Pacific white-sided dolphin and the northern straight dolphin live only in the North Pacific.
Cosmopolitan species may be found in the Pacific, Atlantic and Indian Oceans. However, northern and southern populations become genetically separated over time. In some species, this separation leads eventually to a divergence of the species, such as produced the southern right whale, North Pacific right whale and North Atlantic right whale. Migratory species' reproductive sites often lie in the tropics and their feeding grounds in polar regions.
Thirty-two species are found in European waters, including twenty-five toothed and seven baleen species.
Whale migration.
Many species of whales migrate on a latitudinal basis to move between seasonal habitats. For example, the gray whale migrates 10,000 miles round trip. The journey begins at winter birthing grounds in warm lagoons along Baja California, and traverses 5,000-7,000 miles of coastline to summer feeding grounds in the Bering, Chuckchi and Beaufort seas off the coast of Alaska.
Behaviour.
Sleep.
Conscious breathing cetaceans sleep but cannot afford to be unconscious for long, because they may drown. While knowledge of sleep in wild cetaceans is limited, toothed cetaceans in captivity have been recorded to exhibit unihemispheric slow-wave sleep (USWS), which means they sleep with one side of their brain at a time, so that they may swim, breathe consciously and avoid both predators and social contact during their period of rest.
A 2008 study found that sperm whales sleep in vertical postures just under the surface in passive shallow 'drift-dives', generally during the day, during which whales do not respond to passing vessels unless they are in contact, leading to the suggestion that whales possibly sleep during such dives.
Diving.
While diving, the animals reduce their oxygen consumption by lowering the heart activity and blood circulation; individual organs receive no oxygen during this time. Some rorquals can dive for up to 40 minutes, sperm whales between 60 and 90 minutes and bottlenose whales for two hours. Diving depths average about . Species such as sperm whales can dive to , although more commonly .
Social relations.
Most cetaceans are social animals, although a few species live in pairs or are solitary. A group, known as a pod, usually consists of ten to fifty animals, but on occasion, such as mass availability of food or during mating season, groups may encompass more than one thousand individuals. Inter-species socialization can occur.
Pods have a fixed hierarchy, with the priority positions determined by biting, pushing or ramming. The behavior in the group is aggressive only in situations of stress such as lack of food, but usually it is peaceful. Contact swimming, mutual fondling and nudging are common. The playful behavior of the animals, which is manifested in air jumps, somersaults, surfing, or fin hitting, occurs more often than not in smaller cetaceans, such as dolphins and porpoises.
Whale song.
Males in some baleen species communicate via whale song, sequences of high pitched sounds. These "songs" can be heard for hundreds of kilometers. Each population generally shares a distinct song, which evolves over time. Sometimes, an individual can be identified by its distinctive vocals, such as the 52-hertz whale that sings at a higher frequency than other whales. Some individuals are capable of generating over 600 distinct sounds. In baleen species such as humpbacks, blues and fins, male-specific song is believed to be used to attract and display fitness to females.
Hunting.
Pod groups also hunt, often with other species. Many species of dolphins accompany large tunas on hunting expeditions, following large schools of fish. The killer whale hunts in pods and targets belugas and even larger whales. Humpback whales, among others, form in collaboration bubble carpets to herd krill or plankton into bait balls before lunging at them.
Intelligence.
Cetacea are known to teach, learn, cooperate, scheme and grieve.
Smaller cetaceans, such as dolphins and porpoises, engage in complex play behavior, including such things as producing stable underwater toroidal air-core vortex rings or "bubble rings". The two main methods of bubble ring production are rapid puffing of air into the water and allowing it to rise to the surface, forming a ring, or swimming repeatedly in a circle and then stopping to inject air into the helical vortex currents thus formed. They also appear to enjoy biting the vortex rings, so that they burst into many separate bubbles and then rise quickly to the surface. Whales produce bubble nets to aid in herding prey.
Larger whales are also thought to engage in play. The southern right whale elevates its tail fluke above the water, remaining in the same position for a considerable time. This is known as "sailing". It appears to be a form of play and is most commonly seen off the coast of Argentina and South Africa. Humpback whales also display this behaviour.
Self-awareness appears to be a sign of abstract thinking. Self-awareness, although not well-defined, is believed to be a precursor to more advanced processes such as metacognitive reasoning (thinking about thinking) that humans exploit. Cetaceans appear to possess self-awareness. The most widely used test for self-awareness in animals is the mirror test, in which a temporary dye is placed on an animal's body and the animal is then presented with a mirror. Researchers then explore whether the animal shows signs of self-recognition.
Critics claim that the results of these tests are susceptible to the Clever Hans effect. This test is much less definitive than when used for primates. Primates can touch the mark or the mirror, while cetaceans cannot, making their alleged self-recognition behavior less certain. Skeptics argue that behaviors said to identify self-awareness resemble existing social behaviors, so researchers could be misinterpreting self-awareness for social responses. Advocates counter that the behaviors are different from normal responses to another individual. Cetaceans show less definitive behavior of self-awareness, because they have no pointing ability.
In 1995, Marten and Psarakos used video to test dolphin self-awareness. They showed dolphins real-time footage of themselves, recorded footage and another dolphin. They concluded that their evidence suggested self-awareness rather than social behavior. While this particular study has not been replicated, dolphins later "passed" the mirror test.
Life history.
Reproduction and brooding.
Most cetaceans sexually mature at seven to 10 years. An exception to this is the La Plata dolphin, which is sexually mature at two years, but lives only to about 20. The sperm whale reaches sexual maturity within about 20 years and a lifespan between 50 and 100 years.
For most species, reproduction is seasonal. Ovulation coincides with male fertility. This cycle is usually coupled with seasonal movements that can be observed in many species. Most toothed whales have no fixed bonds. In many species, females choose several partners during a season. Baleen whales are largely monogamous within each reproductive period.
Gestation ranges from 9 to 16 months. Duration is not necessarily a function of size. Porpoises and blue whales gestate for about 11 months. As with all mammals other than marsupials and monotremes, the embryo is fed by the placenta, an organ that draws nutrients from the mother’s bloodstream. Mammals without placentas either lay minuscule eggs (monotremes) or bear minuscule offspring (marsupials).
Cetaceans usually bear one calf. In the case of twins, one usually dies, because the mother cannot produce sufficient milk for both. The fetus is positioned for a tail-first delivery, so that the risk of drowning during delivery is minimal. After birth, the mother carries the infant to the surface for its first breath. At birth they are about one-third of their adult length and tend to be independently active, comparable to terrestrial mammals.
Suckling.
Like other placental mammals, cetaceans give birth to well-developed calves and nurse them with milk from their mammary glands. When suckling, the mother actively splashes milk into the mouth of the calf, using the muscles of her mammary glands, as the calf has no lips. This milk usually has a high fat content, ranging from 16 to 46%, causing the calf to increase rapidly in size and weight.
In many small cetaceans, suckling lasts for about four months. In large species, it lasts for over a year and involves a strong bond between mother and offspring.
The mother is solely responsible for brooding. In some species, so-called "aunts" occasionally suckle the young.
This reproductive strategy provides a few offspring that have a high survival rate.
Lifespan.
Among cetaceans, whales are distinguished by an unusual longevity compared to other higher mammals. Some species, such as the bowhead whale ("Balaena mysticetus"), can reach over 200 years. Based on the annual rings of the bony otic capsule, the age of the oldest known specimen is a male determined to be 211 years at the time of death.
Death.
Upon death, whale carcasses fall to the deep ocean and provide a substantial habitat for marine life. Evidence of whale falls in present-day and fossil records shows that deep-sea whale falls support a rich assemblage of creatures, with a global diversity of 407 species, comparable to other neritic biodiversity hotspots, such as cold seeps and hydrothermal vents.
Deterioration of whale carcasses happens through three stages. Initially, organisms such as sharks and hagfish scavenge the soft tissues at a rapid rate over a period of months and as long as two years. This is followed by the colonization of bones and surrounding sediments (which contain organic matter) by enrichment opportunists, such as crustaceans and polychaetes, throughout a period of years. Finally, sulfophilic bacteria reduce the bones releasing hydrogen sulfide enabling the growth of chemoautotrophic organisms, which in turn, support organisms such as mussels, clams, limpets and sea snails. This stage may last for decades and supports a rich assemblage of species, averaging 185 per site.
Disease.
Brucellosis affects almost all mammals. It is distributed worldwide, while fishing and pollution have caused porpoise population density pockets, which risks further infection and disease spreading. "Brucella ceti", most prevalent in dolphins, has been shown to cause chronic disease, increasing the chance of failed birth and miscarriages, male infertility, neurobrucellosis, cardiopathies, bone and skin lesions, strandings and death. Until 2008, no case had ever been reported in porpoises, but isolated populations have an increased risk and consequentially a high mortality rate.
Evolution.
Phylogenetics.
Molecular biology and immunology show that cetaceans are phylogenetically closely related with the even-toed ungulates (Artiodactyla). Whales direct lineage began in the early Eocene, around 55.8 million years ago, with early artiodactyls. Fossil discoveries at the beginning of the 21st century confirmed this.
Most molecular biological evidence suggests that hippos are the closest living relatives. Common anatomical features include similarities in the morphology of the posterior molars, and the bony ring on the temporal bone (bulla) and the involucre, a skull feature that was previously associated only with cetaceans. The fossil record, however, does not support this relationship, because the hippo lineage dates back only about 15 million years. The most striking common feature is the talus, a bone in the upper ankle. Early cetaceans, archaeocetes, show double castors, which occur only in even-toed ungulates. Corresponding findings are from Tethys Sea deposits in northern India and Pakistan. The Tethys Sea was a shallow sea between the Asian continent and northward-bound Indian plate.
Mysticetes evolved baleen around 25 million years ago and lost their teeth.
Development.
Ancestors.
The direct ancestors of today's cetaceans are probably found within the Dorudontidae whose most famous member, "Dorudon", lived at the same time as "Basilosaurus". Both groups had already developed the typical anatomical features of today's whales, such as hearing. Life in the water for a formerly terrestrial creature required significant adjustments such as the fixed bulla, which replaces the mammalian eardrum, as well as sound-conducting elements for submerged directional hearing. Their wrists were stiffened and probably contributed to the typical build of flippers. The hind legs existed, however, but were significantly reduced in size and with a vestigial pelvis connection.
Transition from land to sea.
The fossil record traces the gradual transition from terrestrial to aquatic life. The regression of the hind limbs allowed greater flexibility of the spine. This made it possible for whales to move around with the vertical tail hitting the water. The front legs transformed into flippers, costing them their mobility on land.
One of the oldest members of ancient cetaceans (Archaeoceti) is "Pakicetus" from the Middle Eocene. This is an animal the size of a wolf, whose skeleton is known only partially. It had functioning legs and lived near the shore. This suggests the animal could still move on land. The long snout had carnivorous dentition.
The transition from land to sea dates to about 49 million years ago, with the "Ambulocetus" ("running whale"), discovered in Pakistan. It was up to long. The limbs of this archaeocete were leg-like, but it was already fully aquatic, indicating that a switch to a lifestyle independent from land happened extraordinarily quickly. The snout was elongated with overhead nostrils and eyes. The tail was strong and supported movement through water. "Ambulocetus" probably lived in mangroves in brackish water and fed in the riparian zone as a predator of fish and other vertebrates.
Dating from about 45 million years ago are species such as "Indocetus", "Kutchicetus", "Rodhocetus" and "Andrewsiphius", all of which were adapted to life in water. The hind limbs of these species were regressed and their body shapes resemble modern whales. Protocetidae family member "Rodhocetus" is considered the first to be fully aquatic. The body was streamlined and delicate with extended hand and foot bones. The merged pelvic lumbar spine was present, making it possible to support the floating movement of the tail. It was likely a good swimmer, but could probably move only clumsily on land, much like a modern seal.
Marine animals.
Since the late Eocene, about 40 million years ago, cetaceans populated the subtropical oceans and no longer emerged on land. An example is the 18-m-long "Basilosaurus", sometimes referred to as "Zeuglodon". The transition from land to water was completed in about 10 million years. The Wadi Al-Hitan ("Whale Valley") in Egypt contains numerous skeletons of "Basilosaurus", as well as other marine vertebrates.
Taxonomy.
Molecular findings and morphological indications suggest that artiodactyls as traditionally defined are paraphyletic with respect to cetaceans. Cetaceans are deeply nested within the former; the two groups together form a monophyletic taxon, for which the name Cetartiodactyla is sometimes used. Modern nomenclature divides Artiodactyla (or Cetartiodactyla) in four subordinate taxa: camelids (Tylopoda), pigs and peccaries (Suina), ruminants (Ruminantia), and hippos plus whales (Whippomorpha).
Cetacea's presumed location within Artiodactyla can be represented in the following cladogram:
Within Cetacea, the two parvorders are baleen whales (Mysticeti) which owe their name to their baleen, and toothed whales (Odontoceti), which have teeth shaped like cones, spades, pegs or tusks, and can perceive their environment through biosonar.
The terms whale and dolphin are informal:
The term 'great whales' covers those currently regulated by the International Whaling Commission:
the Odontoceti families Physeteridae (sperm whales), Ziphiidae (beaked whales), and Kogiidae (pygmy and dwarf sperm whales); and all the Mysticeti families Balaenidae (right and bowhead whales), Cetotheriidae (pygmy right whales), Eschrichtiidae (grey whales), and some of the Balaenopteridae (minke, Bryde's, sei, blue and fin; not Eden's and Omura's whales).
The current classification of living species is as follows:
Status.
Threats.
The primary threats to cetaceans come from people, both directly from whaling or drive hunting and indirect threats from fishing and pollution.
Whaling.
Whaling is the practice of hunting whales, mainly baleen and sperm whales. This activity has gone on since the Stone Age.
In the Middle Ages, reasons for whaling included their meat, oil usable as fuel and the jawbone, which was used in house construction. At the end of the Middle Ages, early whaling fleets aimed at baleen whales, such as bowheads. In the 16th and 17th centuries, the Dutch fleet had about 300 whaling ships with 18,000 crewmen.
In the 18th and 19th centuries, baleen whales especially were hunted for their baleen, which was used as a replacement for wood, or in products requiring strength and flexibility such as corsets and crinoline skirts. In addition, the spermaceti found in the sperm whale was used as a machine lubricant and the ambergris as a material for pharmaceutical and perfume industries. In the second half of the 19th century, the explosive harpoon was invented, leading to a massive increase in the catch size.
Large ships were used as "mother" ships for the whale handlers. In the first half of the 20th century, whales were of great importance as a supplier of raw materials. Whales were intensively hunted during this time; in the 1930s, 30,000 whales were killed. This increased to over 40,000 animals per year up to the 1960s, when stocks of large baleen whales collapsed.
Most hunted whales are now threatened, with some great whale populations exploited to the brink of extinction. Atlantic and Korean gray whale populations were completely eradicated and the North Atlantic right whale population fell to some 300-600. The blue whale population is estimated to be around 14,000.
The first efforts to protect whales came in 1931. Some particularly endangered species, such as the humpback whale (which then numbered about 100 animals), were placed under international protection and the first protected areas were established. In 1946, the International Whaling Commission (IWC) was established, to monitor and secure whale stocks. Whaling of 14 large species for commercial purposes was prohibited worldwide by this organization from 1985 to 2005, though some countries do not honor the prohibition.
The stocks of species such as humpback and blue whales have recovered, though they are still threatened. The United States Congress passed the Marine Mammal Protection Act of 1972 sustain the marine mammal population. It prohibits the taking of marine mammals except for several hundred per year taken in Alaska. Japanese whaling ships are allowed to hunt whales of different species for ostensibly scientific purposes.
Aboriginal whaling is still permitted. About 1,200 pilot whales were taken in the Faroe Islands in 2017, and about 900 narwhals and 800 belugas per year are taken in Alaska, Canada, Greenland, and Siberia. About 150 minke are taken in Greenland per year, 120 gray whales in Siberia and 50 bowheads in Alaska, as aboriginal whaling, besides the 600 minke taken commercially by Norway, 300 minke and 100 sei taken by Japan and up to 100 fin whales taken by Iceland. Iceland and Norway do not recognize the ban and operate commercial whaling. Norway and Japan are committed to ending the ban.
Dolphins and other smaller cetaceans are sometimes hunted in an activity known as dolphin drive hunting. This is accomplished by driving a pod together with boats, usually into a bay or onto a beach. Their escape is prevented by closing off the route to the ocean with other boats or nets. Dolphins are hunted this way in several places around the world, including the Solomon Islands, the Faroe Islands, Peru and Japan (the most well-known practitioner). Dolphins are mostly hunted for their meat, though some end up in dolphinaria. Despite the controversy thousands of dolphins are caught in drive hunts each year.
Fishing.
Dolphin pods often reside near large tuna shoals. This is known to fishermen, who look for dolphins to catch tuna. Dolphins are much easier to spot from a distance than tuna, since they regularly breathe. The fishermen pull their nets hundreds of meters wide in a circle around the dolphin groups, in the expectation that they will net a tuna shoal. When the nets are pulled together, the dolphins become entangled under water and drown. Line fisheries in larger rivers are threats to river dolphins.
A greater threat than by-catch for small cetaceans is targeted hunting. In Southeast Asia, they are sold as fish-replacement to locals, since the region's edible fish promise higher revenues from exports. In the Mediterranean, small cetaceans are targeted to ease pressure on edible fish.
Strandings.
A stranding is when a cetacean leaves the water to lie on a beach. In some cases, groups of whales strand together. The best known are mass strandings of pilot whales and sperm whales. Stranded cetaceans usually die, because their as much as body weight compresses their lungs or breaks their ribs. Smaller whales can die of heatstroke because of their thermal insulation.
The causes are not clear. Possible reasons for mass beachings are:
Since 2000, whale strandings frequently occurred following military sonar testing. In December 2001, the US Navy admitted partial responsibility for the beaching and the deaths of several marine mammals in March 2000. The coauthor of the interim report stated that animals killed by active sonar of some Navy ships were injured. Generally, underwater noise, which is still on the increase, is increasingly tied to strandings; because it impairs communication and sense of direction.
Climate change influences the major wind systems and ocean currents, which also lead to cetacean strandings. Researchers studying strandings on the Tasmanian coast from 1920–2002 found that greater strandings occurred at certain time intervals. Years with increased strandings were associated with severe storms, which initiated cold water flows close to the coast. In nutrient-rich, cold water, cetaceans expect large prey animals, so they follow the cold water currents into shallower waters, where the risk is higher for strandings. Whales and dolphins who live in pods may accompany sick or debilitated pod members into shallow water, stranding them at low tide.
Environmental hazards.
Heavy metals, residues of many plant and insect venoms and plastic waste flotsam are not biodegradable. Sometimes, cetaceans consume these hazardous materials, mistaking them for food items. As a result, the animals are more susceptible to disease and have fewer offspring.
Damage to the ozone layer reduces plankton reproduction because of its resulting radiation. This shrinks the food supply for many marine animals, but the filter-feeding baleen whales are most impacted. Even the Nekton is, in addition to intensive exploitation, damaged by the radiation.
Food supplies are also reduced long-term by ocean acidification due to increased absorption of increased atmospheric carbon dioxide. The CO2 reacts with water to form carbonic acid, which reduces the construction of the calcium carbonate skeletons of food supplies for zooplankton that baleen whales depend on.
The military and resource extraction industries operate strong sonar and blasting operations. Marine seismic surveys use loud, low-frequency sound that show what is lying underneath the Earth's surface. Vessel traffic also increases noise in the oceans. Such noise can disrupt cetacean behavior such as their use of biosonar for orientation and communication. Severe instances can panic them, driving them to the surface. This leads to bubbles in blood gases and can cause decompression sickness. Naval exercises with sonar regularly results in fallen cetaceans that wash up with fatal decompression. Sounds can be disruptive at distances of more than . Damage varies across frequency and species.
Relationship to humans.
Research history.
In Aristotle's time, the 4th century BCE, whales were regarded as fish due to their superficial similarity. Aristotle, however, observed many physiological and anatomical similarities with the terrestrial vertebrates, such as blood (circulation), lungs, uterus and fin anatomy. His detailed descriptions were assimilated by the Romans, but mixed with a more accurate knowledge of the dolphins, as mentioned by Pliny the Elder in his "Natural history". In the art of this and subsequent periods, dolphins are portrayed with a high-arched head (typical of porpoises) and a long snout. The harbour porpoise was one of the most accessible species for early cetologists; because it could be seen close to land, inhabiting shallow coastal areas of Europe. Much of the findings that apply to all cetaceans were first discovered in porpoises. One of the first anatomical descriptions of the airways of a harbor porpoise dates from 1671 by John Ray. It nevertheless referred to the porpoise as a fish.
In the 10th edition of Systema Naturae (1758), Swedish biologist and taxonomist Carl Linnaeus asserted that cetaceans were mammals and not fish. His groundbreaking binomial system formed the basis of modern whale classification.
Culture.
Cetaceans play a role in human culture.
Prehistoric.
Stone Age petroglyphs, such as those in Roddoy and Reppa (Norway), and the Bangudae Petroglyphs in South Korea, depict them. Whale bones were used for many purposes. In the Neolithic settlement of Skara Brae on Orkney sauce pans were made from whale vertebrae.
Antiquity.
The whale was first mentioned in ancient Greece by Homer. There, it is called Ketos, a term that initially included all large marine animals. From this was derived the Roman word for whale, Cetus. Other names were phálaina (Aristotle, Latin form of ballaena) for the female and, with an ironic characteristic style, musculus (Mouse) for the male. North Sea whales were called Physeter, which was meant for the sperm whale "Physter macrocephalus". Whales are described in particular by Aristotle, Pliny and Ambrose. All mention both live birth and suckling. Pliny describes the problems associated with the lungs with spray tubes and Ambrose claimed that large whales would take their young into their mouth to protect them.
In the Bible especially, the leviathan plays a role as a sea monster. The essence, which features a giant crocodile or a dragon and a whale, was created according to the Bible by God and should again be destroyed by him. In the Book of Job, the leviathan is described in more detail.
In Jonah there is a more recognizable description of a whale alongside the prophet Jonah, who, on his flight from the city of Nineveh is swallowed by a whale.
Dolphins are mentioned far more often than whales. Aristotle discusses the sacred animals of the Greeks in his "Historia Animalium" and gives details of their role as aquatic animals. The Greeks admired the dolphin as a "king of the aquatic animals" and referred to them erroneously as fish. Its intelligence was apparent both in its ability to escape from fishnets and in its collaboration with fishermen.
River dolphins are known from the Ganges and – erroneously – the Nile. In the latter case it was equated with sharks and catfish. Supposedly they attacked even crocodiles.
Dolphins appear in Greek mythology. Because of their intelligence, they rescued multiple people from drowning. They were said to love music – probably not least because of their own song – they saved, in the legends, famous musicians such as Arion of Lesbos from Methymna or Kairanos from Miletus. Because of their mental faculties, dolphins were considered for the god Dionysus.
Dolphins belong to the domain of Poseidon and led him to his wife Amphitrite. Dolphins are associated with other gods, such as Apollo, Dionysus and Aphrodite. The Greeks paid tribute to both whales and dolphins with their own constellation. The constellation of the Whale (Ketos, lat. Cetus) is located south of the Dolphin (Delphi, lat. Delphinus) north of the zodiac.
Ancient art often included dolphin representations, including the Cretan Minoans. Later they appeared on reliefs, gems, lamps, coins, mosaics and gravestones. A particularly popular representation is that of Arion or the Taras (mythology) riding on a dolphin. In early Christian art, the dolphin is a popular motif, at times used as a symbol of Christ.
Middle Ages to the 19th century.
St. Brendan described in his travel story "Navigatio Sancti Brendani" an encounter with a whale, between the years 565–573. He described how he and his companions entered a treeless island, which turned out to be a giant whale, which he called Jasconicus. He met this whale seven years later and rested on his back.
Most descriptions of large whales from this time until the whaling era, beginning in the 17th century, were of beached whales, which resembled no other animal. This was particularly true for the sperm whale, the most frequently stranded in larger groups. Raymond Gilmore documented seventeen sperm whales in the estuary of the Elbe from 1723 to 1959 and thirty-one animals on the coast of Great Britain in 1784. In 1827, a blue whale beached itself off the coast of Ostend. Whales were used as attractions in museums and traveling exhibitions.
Whalers from the 17th to 19th centuries depicted whales in drawings and recounted tales of their occupation. Although they knew that whales were harmless giants, they described battles with harpooned animals. These included descriptions of sea monsters, including huge whales, sharks, sea snakes, giant squid and octopuses.
Among the first whalers who described their experiences on whaling trips was Captain William Scoresby from Great Britain, who published the book "Northern Whale Fishery", describing the hunt for northern baleen whales. This was followed by Thomas Beale, a British surgeon, in his book "Some observations on the natural history of the sperm whale" in 1835; and Frederick Debell Bennett's "The tale of a whale hunt" in 1840. Whales were described in narrative literature and paintings, most famously in the novels "Moby Dick" by Herman Melville and "20,000 Leagues Under the Sea" by Jules Verne.
Baleen was used to make vessel components such as the bottom of a bucket in the Scottish National Museum. The Norsemen crafted ornamented plates from baleen, sometimes interpreted as ironing boards.
In the Canadian Arctic (east coast) in Punuk and Thule culture (1000–1600 C.E.), baleen was used to construct houses in place of wood as roof support for winter houses, with half of the building buried under the ground. The actual roof was probably made of animal skins that were covered with soil and moss.
Modern culture.
In the 20th century perceptions of cetaceans changed. They transformed from monsters into creatures of wonder, as science revealed them to be intelligent and peaceful animals. Hunting was replaced by whale and dolphin tourism. This change is reflected in films and novels. For example, the protagonist of the series Flipper was a bottle-nose dolphin. The TV series SeaQuest DSV (1993–1996), the movies Free Willy, and the book series The Hitchhiker's Guide to the Galaxy by Douglas Adams are examples.
The study of whale song also produced a popular album, "Songs of the Humpback Whale".
Captivity.
Whales and dolphins have been kept in captivity for use in education, research and entertainment since the 19th century.
Belugas.
Beluga whales were the first whales to be kept in captivity. Other species were too rare, too shy or too big. The first was shown at Barnum's Museum in New York City in 1861. For most of the 20th century, Canada was the predominant source. They were taken from the St. Lawrence River estuary until the late 1960s, after which they were predominantly taken from the Churchill River estuary until capture was banned in 1992. Russia then became the largest provider. Belugas are caught in the Amur Darya delta and their eastern coast and are transported domestically to aquaria or dolphinaria in Moscow, St. Petersburg and Sochi, or exported to countries such as Canada. They have not been domesticated.
As of 2006, 30 belugas lived in Canada and 28 in the United States. 42 deaths in captivity had been reported. A single specimen can reportedly fetch up to US$100,000 (GB£64,160). The beluga's popularity is due to its unique color and its facial expressions. The latter is possible because while most cetacean "smiles" are fixed, the extra movement afforded by the beluga's unfused cervical vertebrae allows a greater range of apparent expression.
Killer whales.
The killer whale's intelligence, trainability, striking appearance, playfulness in captivity and sheer size have made it a popular exhibit at aquaria and aquatic theme parks. From 1976 to 1997, fifty-five whales were taken from the wild in Iceland, nineteen from Japan and three from Argentina. These figures exclude animals that died during capture. Live captures fell dramatically in the 1990s and by 1999, about 40% of the forty-eight animals on display in the world were captive-born.
Organizations such as World Animal Protection and the Whale and Dolphin Conservation campaign against the practice of keeping them in captivity.
In captivity, they often develop pathologies, such as the dorsal fin collapse seen in 60–90% of captive males. Captives have reduced life expectancy, on average only living into their 20s, although some live longer, including several over 30 years old and two, Corky II and Lolita, in their mid-40s. In the wild, females who survive infancy live 46 years on average and up to 70–80 years. Wild males who survive infancy live 31 years on average and can reach 50–60 years.
Captivity usually bears little resemblance to wild habitat and captive whales' social groups are foreign to those found in the wild. Critics claim captive life is stressful due to these factors and the requirement to perform circus tricks that are not part of wild killer whale behavior. Wild killer whales may travel up to in a day and critics say the animals are too big and intelligent to be suitable for captivity. Captives occasionally act aggressively towards themselves, their tankmates, or humans, which critics say is a result of stress. Killer whales are well known for their performances in shows, but the number of orcas kept in captivity is small, especially when compared to the number of bottlenose dolphins, with only forty-four captive orcas being held in aquaria as of 2012.
Each country has its own tank requirements; in the US, the minimum enclosure size is set by the Code of Federal Regulations, 9 CFR E § 3.104, under the "Specifications for the Humane Handling, Care, Treatment and Transportation of Marine Mammals".
Aggression among captive killer whales is common. They attack each other and their trainers as well. In 2013, SeaWorld's treatment of killer whales in captivity was the basis of the movie "Blackfish", which documents the history of Tilikum, a killer whale at SeaWorld Orlando, who had been involved in the deaths of three people. The film led to proposals by some lawmakers to ban captivity of cetaceans, and led SeaWorld to announce in 2016 that it would phase out its killer whale program after various unsuccessful attempts to restore its revenues, reputation, and stock price.
Others.
Dolphins and porpoises are kept in captivity. Bottlenose dolphins are the most common, as they are relatively easy to train, have a long lifespan in captivity and have a friendly appearance. Bottlenose dolphins live in captivity across the world, though exact numbers are hard to determine. Other species kept in captivity are spotted dolphins, false killer whales and common dolphins, Commerson's dolphins, as well as rough-toothed dolphins, but all in much lower numbers. There are also fewer than ten pilot whales, Amazon river dolphins, Risso's dolphins, spinner dolphins, or tucuxi in captivity. Two unusual and rare hybrid dolphins, known as wolphins, are kept at Sea Life Park in Hawaii, which is a cross between a bottlenose dolphin and a false killer whale. Also, two common/bottlenose hybrids reside in captivity at Discovery Cove and SeaWorld San Diego.
In repeated attempts in the 1960s and 1970s, narwhals kept in captivity died within months. A breeding pair of pygmy right whales were retained in a netted area. They were eventually released in South Africa. In 1971, SeaWorld captured a California gray whale calf in Mexico at Scammon's Lagoon. The calf, later named Gigi, was separated from her mother using a form of lasso attached to her flukes. Gigi was displayed at SeaWorld San Diego for a year. She was then released with a radio beacon affixed to her back; however, contact was lost after three weeks. Gigi was the first captive baleen whale. JJ, another gray whale calf, was kept at SeaWorld San Diego. JJ was an orphaned calf that beached itself in April 1997 and was transported two miles to SeaWorld. The calf was a popular attraction and behaved normally, despite separation from his mother. A year later, the then whale though smaller than average, was too big to keep in captivity, and was released on April 1, 1998. A captive Amazon river dolphin housed at Acuario de Valencia is the only trained river dolphin in captivity.
Here is a list of all the cetaceans that have been taken into captivity for either conservation or human entertainment purposes currently or in the past, temporarily or permanently.


Keyseria

Keyseria is an extinct genus of dicynodont therapsid. The type species "K. benjamini" was first named in 1948 as "Dicynodon benjamini".


Junornis

Junornis is a bird genus, belonging to the Enantiornithes, that during the Early Cretaceous lived in the area of present China.
Discovery.
At Liutiaogou village, near the town of Daming in Ningcheng County, Inner-Mongolia, a bird skeleton was excavated that was acquired by the Beijing Museum of Natural History. It was further prepared by Maureen Walsh.
In 2017 Liu Di, Luis M. Chiappe, Francisco Serrano, Michael Habib, Zhang Yuguang and Meng Qinjing named and described the type species "Junornis houi". The generic name is derived from Chinese "jun", 俊, "beautiful", and Greek "ornis", "bird". The specific name honours the Chinese paleoorntithologist Hou Lianhai.
The holotype, BMNHC-PH 919, was found in a layer of the Yixian Formation that is roughly 126 million years old. It consists of a skeleton with skull, compressed on a plate and counterplate. The skeleton is largely associated, though the skull is detached. Bone conservation is excellent. Extensive remains of the plumage have been preserved.


Crossota rufobrunnea

Crossota rufobrunnea is a species of hydrozoan.


Carotid sinus

In human anatomy, the carotid sinus is a dilated area at the base of the internal carotid artery just superior to the bifurcation of the internal carotid and external carotid at the level of the superior border of thyroid cartilage. The carotid sinus extends from the bifurcation to the "true" internal carotid artery. The carotid sinus is sensitive to pressure changes in the arterial blood at this level. It is the major baroreception site in humans and most mammals.
Structure.
The carotid sinus is the reflex area of the carotid artery, consisting of baroreceptors which monitor blood pressure.
Function.
The carotid sinus contains numerous baroreceptors which function as a "sampling area" for many homeostatic mechanisms for maintaining blood pressure. The carotid sinus baroreceptors are innervated by the carotid sinus nerve, which is a branch of the glossopharyngeal nerve (CN IX). The neurons which innervate the carotid sinus centrally project to the solitary nucleus in the medulla of the brainstem. The solitary nucleus indirectly modulates the activity of sympathetic and parasympathetic neurons in the medulla and pons through the hypothalamus. These neurons then regulate the autonomic control of the heart and blood vessels. The aortic arch baroreceptors are innervated by the aortic nerve (nerve of Cyon, Ludwig nerve), which combines with CN X (vagus nerve) and travels to the NTS.
Clinical significance.
It is a sensitive site of the body because stimulation can drive large-scale reflex effects throughout the body. This can be used therapeutically in treatment of resistant hypertension by baroreflex activation. Physical assault at this point, producing massive baroreflex activation can cause dramatic falls in blood pressure and cerebral ischemia.
Disease.
The carotid sinus often has atherosclerotic plaques because of disturbed hemodynamics (low wall shear stress, flow reversal/recirculation). Since these plaques, if large and unstable, predispose to ischemic strokes and transient ischemic attacks, carotid endarterectomies are frequently done for prophylaxis.
The carotid sinus can be oversensitive to manual stimulation, a condition known as carotid sinus hypersensitivity, carotid sinus syndrome or carotid sinus syncope, in which manual stimulation causes large changes in heart rate and/or blood pressure. This classically presents as a patient who has "fainted" (actually a presyncope) on several occasions while shaving, or in some other way coming into contact with their carotid sinus.
Carotid sinus syndrome is a temporary loss of consciousness that sometimes accompanies convulsive seizures because of the intensity of the carotid sinus reflex when pressure builds in one or both carotid sinuses.
Treatment of resistant hypertension.
Stimulation of baroreceptors at the carotid sinus can be used to treat resistant hypertension via activation of the baroreflex. A pacemaker-like device can be implanted to electrically stimulate the receptors chronically, which is found to lower blood pressure by 15–25 mmHg.
Massage.
Massage of the carotid sinus, carotid sinus massage is used to diagnose carotid sinus syncope and is sometimes useful for differentiating supraventricular tachycardia (SVT) from ventricular tachycardia. Like the valsalva maneuver, it is a treatment for acute SVT. It is less effective than pharmaceutical management of SVT with verapamil or adenosine, but it is still the preferred first line of treatment in a hemodynamically stable patient.
Carotid sinus reflex death.
Carotid sinus reflex death is a potential etiology of sudden death in which manual stimulation of the carotid sinus allegedly causes strong glossopharyngeal nerve (Vagus nerve is for aortic arch baroreceptors) impulses leading to terminal cardiac arrest. Carotid sinus reflex death has been pointed out as a possible cause of death in cases of strangulation, hanging and autoerotic strangulation, but such deductions remain controversial. Medical literature examining the use of carotid sinus massage involving brief gentle pressure of the carotid sinus in therapeutic settings as a diagnostic and therapeutic examination tool have reported few potentially fatal complications. A carotid massage can also possibly dislodge a thrombus, or some plaque. This could lead to any number of life-threatening effects, including stroke.
In martial arts and self defense.
Stimulation of the carotid sinus via a slap or a strike, to induce (usually temporary, but sometimes lethal) loss of consciousness is a theatrical self-defense technique, and is often taught in martial arts such as karate.


Ichthyolith

An ichthyolith (from Greek, “fish“ and ”stone”, “rock“, literally "fish-rock") is any disarticulated remains of a fish found in the fossil record, most often a scale, denticle or tooth.
The term was coined by Doyle, Kennedy and Riedel (1974) to denote 'fish skeletal debris'.
The term 'stratignathy', proposed in the same paper for the time relationships of ichthyoliths, did not gain currency.


Claraia

Claraia is an extinct genus of scallop-like bivalve molluscs that lived from the Capitanian stage of the Late Permian to the Anisian stage of the Middle Triassic, 266-237 million years ago. Fossils have been found worldwide in North America, Europe, Asia, Africa, and Australia. These are common fossils subsequent to the Permian-Triassic boundary, suggesting that the genus experienced rapid diversification during and after the Permian–Triassic extinction event, around 251.4 million years ago.
Ecology.
"Claraia" may have been an opportunistic genus that filled the niche of many benthic invertebrates such as brachiopods that were heavily impacted by the extinction. A narrowing of the byssal notch and a trend towards a smoother shell in species of "Claraia" over time may have led to increased mobility. This increase in mobility may have been an advantage over more sessile animals during the extinction event. It is thought to have lived in anoxic waters at great depths, and therefore may have been better adapted for the anoxic event that may have occurred during the Permian–Triassic extinction event.


Carinatae

Carinatae is the group of all birds and their extinct relatives to possess a keel, or "carina", on the underside of the breastbone used to anchor large flight muscles.
Classification.
Definition.
Traditionally, Carinatae were defined as all birds whose sternum (breast bone) has a keel ("carina"). The keel is a strong median ridge running down the length of the sternum. This is an important area for the attachment of flight muscles. Thus, all flying birds have a pronounced keel. Ratites, all of which are flightless, lack a strong keel. Thus, living birds were divided into carinatae (keeled) and ratites (from "ratis", "raft", referring to the flatness of the sternum). The difficulty with this scheme phylogenetically was that some flightless birds, without strong keels, are descended directly from ordinary flying birds possessing one. Examples include the kakapo, a flightless parrot, and the dodo, a columbiform (the pigeon family). Neither of these birds are a ratite. Thus, this supposedly distinctive feature was easy to use, but had nothing to do with actual phylogenetic relationship.
Beginning in the 1980s, Carinatae was given several phylogenetic definitions. The first was as a node-based clade uniting "Ichthyornis" with modern birds. However, in many analyses, this definition would be synonymous with the more widely used name Ornithurae. An alternate definition was provided in 2001, naming Carinatae an apomorphy-based clade defined by the presence of a keeled sternum.
The most primitive known bird relative with a keeled breastbone is "Confuciusornis". While some specimens of this stem-bird have flat breastbones, some show a small ridge that could have supported a cartilaginous keel.


Walter Pfeffer Dando

Walter Pfeffer Dando (1852–1944, some sources 1854) was a British stage engineer and early film director. Among his developments and patents were those for a device allowing theatre actors to "fly" about the stage (by 1875) and improvements to the technology for tableaux vivants. Dando also served as an official photographer to the Zoological Society of London.
Dando was the stage manager of the Palace Theatre (1891–1896) before leaving to establish his own business screening "phantom rides", first-person travel footage from trains.
Personal life.
Dando attended Southgate College and (date unknown) began work in the counting-house of William Whiteley, Westbourne Grove. He became a member of Whiteley's amateur dramatic club – the Kildare. In 1875 Patented apparatus for flying effects (Patent no. 3067 1875) On 12 April 1877, St Saviour's Church, Hoxton, married Letitia Barry, stage name, Mlle Aenea, "the original flying dancer". Daughter of actors William and Letitia Barry, sister of Katie Barry and Mlle Ariel, niece of George Conquest.
1877 Advertised as maker and supplier of "India-rubber springs for gymnastic or theatrical purposes" (also advertised as "India-rubber spring and chest-expander manufacturer")
In 1879, their only child, Letitia Mary Ann Emma 'Queenie' Dando, was born. Following the death of his daughter in 1921 and his wife in 1928, Dando married the much younger dancer, Letitia Daisy Paver, in 1929.


Psilotrisauropus

Psilotrisauropus is an ichnogenus of reptile footprint.


Cape Hay

Cape Hay is an uninhabited headland on Bylot Island in the Qikiqtaaluk Region of Nunavut, Canada. It is located at the island's northwestern tip, protruding into Lancaster Sound. The Wollaston Islands are offshore.
It is named in honor of Admiral Sir John Hay, Secretary of the Royal Navy.
Geography.
The habitat is characterized by coastal cliffs, rocky shores, and tundra. The elevation can reach above sea level. It is in size.
Conservation.
The cape is a Canadian Important Bird Area (#NU004) and an International Biological Program site. It is situated within the Bylot Island Migratory Bird Sanctuary and the Sirmilik (North Baffin) National Park. Other IBAs on the island include Cape Graham Moore and the Southwest Bylot plain.
Avifauna.
Notable bird species include the black-legged kittiwake and thick-billed murre, both of which are colonial seabirds. The area is also frequented by narwhals, polar bears, harp seals, ringed seals and white whales


Parascon

Parascon is a genus of water bear or moss piglet, a tardigrade in the class Eutardigrada.


Hediste

Hediste is a genus of annelids belonging to the family Nereididae.
The species of this genus are found in Europe, Japan and Northern America.
Species.
Species in this genus include:


Laryngeal cavity

The laryngeal cavity (cavity of the larynx) extends from the laryngeal inlet downwards to the lower border of the cricoid cartilage where it is continuous with that of the trachea.
It is divided into two parts by the projection of the vocal folds, between which is a narrow triangular opening, the rima glottidis.
The portion of the cavity of the larynx above the vocal folds is called the vestibule; it is wide and triangular in shape, its base or anterior wall presenting, however, about its center the backward projection of the tubercle of the epiglottis.
It contains the vestibular folds, and between these and the vocal folds are the ventricles of the larynx.
The portion below the vocal folds is called the infraglottic cavity. It is at first of an elliptical form, but lower down it widens out, assumes a circular form, and is continuous with the tube of the trachea.


Phoenicopterus


Rudolphina Menzel

Dr. Rudolphina Menzel (1891–1973) was a cynologist, best known for her work in the field of animal behavior, from Vienna, Austria.
Prof. Menzel was responsible for gaining recognition for the Canaan Dog; and she wrote the breed standard, which was accepted by the FCI in 1966.
History.
She immigrated with her husband Dr Rudolph Menzel to Palestine in 1938.
She was asked by the Haganah for help in setting up a dog section (forerunner to what would become Unit Oketz). Dr. Menzel found that the standard breeds used for guarding, tracking and other tasks were unable to cope with the harsh climate and terrain, so she sought an alternative, turning to the local pariah dog.
She began a redomestication program of the pariah dogs living on the outskirts of settlements and with the Bedouin in the desert. She collected puppies and adults, and found them to be highly adaptable, amenable to domestication, and quick to learn.
Menzel's Canaan Dog breeding program was concentrated with the Institute where a foundation of kennel-raised Canaan Dogs was established, carrying the name "B'nei Habitachon".
In 1965, she exported the four Canaan Dogs to the United States, and later sent specimens of the breed to Germany.
Menzel sent a male Canaan Dog to Mrs Connie Higgins in the United Kingdom. In 1964, Mrs. Higgins had already acquired a female puppy from a wild litter in Damascus, and on 28 December 1969, she bred the first known litter of Canaan Dogs born in the United Kingdom.
In 1970, Shaar Hagai Kennels, located near Jerusalem, worked closely with Dr. Menzel in the development and breeding of the breed, and continued her work after her death in 1973.


West African worm lizard

The West African worm lizard ("Baikia africana") is a species of amphisbaenian in the family Amphisbaenidae. The species is endemic to Nigeria.
Taxonomy.
"B. africana" is the only species in the genus Baikia.


Chen Kunshu

Chen Kunshu (; died May 1864), prominent military leader of the Taiping Rebellion, and known during his military tenure as the King of Hu (護王) (means Prince Protector). He led Taiping forces to many military victories especially the Second rout the Army Group Jiangnan. He was executed by Li Hongzhang after interrogation in 1864, Chen was an important General and was the sole person responsible for the late-Taiping Rebellion.
Li Hongzhang used Chen to balance Li Xiucheng's power, which was originally justified, but grew too large.
Wins.
Eastern campaign
It made Zeng Guofan offer a reward of 50,000 silver tael to arrest alive Chen and death 25,000 tael(then a soldier salary was 2 silver tael one month ).
Western campaign


Midbody (cell biology)

The midbody is a transient structure found in mammalian cells and is present near the end of cytokinesis just prior to the complete separation of the dividing cells. The structure was first described by Walther Flemming in 1891. The central section of a midbody was named after Flemming and is called the Flemming body.
The midbody structure contains bundles of microtubules derived from the mitotic spindle which compacts during the final stages of cell division. It has a typical diameter of 1 micrometre and a length of 3 to 5 micrometres. Aside from microtubules it also contains various proteins involved in cytokinesis, asymmetric cell division, and chromosome segregation. The midbody is important for completing the final stages of cytokinesis, a process called abscission, although its precise role in these processes is not clear.


Notoplanidae

Notoplanidae is family of free-living marine turbellarian flatworms in the order Polycladida, sub order Acotylea.


Dalytyphloplanida

Dalytyphloplanida is a suborder of rhabdocoel flatworms. It contains about 1000 species and has a cosmopolitan distribution in both marine and freshwater environments, with several groups having comensal or parasitic lifestyles.
Description.
The suborder Dalytyphloplanida was recently erected based on molecular evidences and few synapomorphies are known. The possible identified synapomorphies include the presence of small dense granules, as well as an axonemal spur and a group of longitudinal microtubules in sperm cells.
Classification.
Traditionally, members of the suborder Dalytyphloplanida were classified into two groups: Dalyellioida and Typhloplanoida, although both were poorly characterized morphologically. Recent molecular studies revealed that those two groups were not separated clades and both were merged in the clade Dalytyphloplanida.
Within Dalytyphloplanida two clades were found: Neodalyellida, formed by marine species of the former group Dalyellioida, some of which are parasites, and Neotyphloplanida, which includes a clade of marine species of the former Typhloplanoida (Thalassotyphloplanida) and one of freshwater species (Limnotyphloplanida). However, synapomorphies for these newly erected clades are not yet known.


Epiperipatus ohausi

Epiperipatus ohausi is a species of velvet worm in the family Peripatidae.


Orchesella pseudobifasciata

Orchesella pseudobifasciata is a species of slender springtail in the family Entomobryidae.


Ernstia laxa

Ernstia laxa is a species of calcareous sponge in the family Clathrinidae found in New Zealand. The species name is derived from Latin meaning "wide".
Description.
This species is similar to "Ascaltis reticulum" except it has wider and thicker actines. More research is needed to confirm the correct classification of this organism.
References.
World Register of Marine Species entry


Solitaire (bird)

The solitaires are medium-sized mostly insectivorous birds in the genera "Myadestes", "Cichlopsis" and "Entomodestes" of the thrush family Turdidae.
Taxonomy.
Although all three genera of solitaires are morphologically similar, genetic studies have indicated that they are not particularly closely related. The genus "Myadestes" is in the basal clade of the family Turdidae, along with the genera "Sialia" (the bluebirds) and "Neocossyphus" (African ant-thrushes).
Species list.
Thrushes in three genera are called "solitaires":


Anacropora

Anacropora is a genus of stony corals in the Acroporidae family. They are sometimes called briar corals and there are seven known species.
Description.
Members of this genus are generally fragile corals with branches less than ten centimetres long which form small colonies. The branches are either spreading or may be clustered and are sometimes fused together. The calices are rounded and up to one millimetre in diameter. The area between the calices is porous with numerous small tubercles. There are no axial corallites and the main septa number six with a few more subsidiary ones. The small radial corallites have an ‘empty’ appearance similar to "Montipora". The delicate tentacles can often be seen extended during the day.
Distribution.
Members of this genus occur in the Indian Ocean and the western Pacific being found mostly in muddy waters. They are generally uncommon and are not a reef species.


Accessory bone

An accessory bone or supernumerary bone is a bone that is not normally present in the body, but can be found as a variant in a significant number of people. It poses a risk of being misdiagnosed as bone fractures on radiography.
Wrist and hand.
Os ulnostyloideum.
The "os ulnostyloideum" is an ulnar styloid process that is not fused to the rest of the ulna bone. On X-rays, an "os ulnostyloideum" is sometimes mistaken for an avulsion fracture of the styloid process. However, the distinction between these is extremely difficult. It is alleged that the os ulnostyloideum has a close relationship with or is synonymous with the os triquetrum secundarium.
Os centrale.
The "os carpi centrale" (also briefly "os centrale") is, where present, located on the dorsal side of the wrist between the scaphoid, the trapezoid and capitate, radially to the deep fossa of the capitate. The bone is present in almost every human embryo of 17–49 mm length, but then usually fuses with the ulnar side of the scaphoid. Sometimes it fuses with the capitate or the trapezoid. The literature also refers to an "os centrale" at the palm of the carpus, but this existence is questioned.
In most primates, including orangutangs and gibbons, the os centrale is an independent bone that is attached to the scaphoid by strong ligaments. Conversely, in African apes and humans, the os centrale normally fuses to the scaphoid early in development. In chimpanzees, the bone fuses with the scaphoid first after birth, while in gibbons and orangutans this occurs first at older age. A good number of scholars have construed the scaphoid-centrale fusion as a functional adaptation to knuckle-walking, since a fused morphology would better cope with the increased shear stress on this joint during this kind of quadrupedal locomotion. The results from a simulation study have shown that fused scaphoid-centrales show lower stress values as compared to non fused morphologies, thus supporting a biomechanical explanation for the scaphoid-centrale fusion as a functional adaptation for knuckle-walking.
Ankle.
Accessory bones at the ankle mainly include:
"Os trigonum" (further described below) may also be seen on an ankle X-ray.
Foot.
Accessory navicular.
An accessory navicular bone, also called "os tibiale externum", occasionally develops in front of the ankle towards the inside of the foot. This bone may be present in approximately 2–21% of the general population and is usually asymptomatic. When it is symptomatic, surgery may be necessary.
The Geist classification divides the accessory navicular bones into three types.
Os trigonum.
The "os trigonum" or "accessory talus" represents a failure of fusion of the lateral tubercle of the posterior process of the talus bone. Is estimated to be present in 7–25% of adults. It can be mistaken for an avulsion fracture of lateral tubercle of talus (Shepherd fracture) or a fracture of the Stieda process. In most cases, Os Trigonum will go unnoticed, but with some ankle injuries it can get trapped between the heel and ankle bones which irritates the surrounding structures, leading to Os Trigonum Syndrome.
Other locations.
Neck:
Shoulder:
Vertebral column:
Knee


Notopalaeognathae

Notopalaeognathae is a clade that contains the order Rheiformes (rheas), the clade Novaeratitae (birds such as the kiwis and the emus), the order Tinamiformes (tinamous) and the extinct order Dinornithiformes (the moas). The exact relationships of this group have only recently been understood, with tinamous and the moas sharing a common ancestor and the kiwis being more closely related to emus and cassowaries. The extinct elephant birds of Madagascar have recently been identified as closest relative to the kiwis. The rheas are either the basal most branch of notopalaeognaths or the sister group to Novaeratitae. The sister group to Notopalaeognathae is Struthionidae (the ostrich family).


Circulus arteriosus major

Circulus arteriosus major, also called "major circulus arteriosus of iris" CIA or CIAM, is formed by anastomosis of the anterior ciliary arteries with the Long posterior ciliary arteries at the ciliary body. It supplies the iris, ciliary body and choroid.
The veinous drainage of CIA is : 4 vortex veins that drain into the ophthalmic vein.


William Frederick Purcell

William Frederick Purcell (18 September 1866 - 3 October 1919) was an English-born South African arachnologist and zoologist. He is regarded as being the founder of modern araneology in South Africa.
Early life and education.
Purcell was born in London, England to Dr Walter P.J. Purcell of Waterford, Ireland, and his wife Sophia W.J. Hertzog of Cape Town. In 1868 the family moved to South Africa and settled in Cape Town. He spent most of his childhood on the farm Bergvliet, which was owned by his uncle W.F. Hertzog.
From 1881, Purcell studied at South African College, Cape Town, matriculated through the University of the Cape of Good Hope (UCGH) in 1884 and received a BA (with Honours) in mathematics and natural science in 1887 from UCGH. In 1885 and 1887 he provided the South African Museum with samples of "coleoptera" obtained at Bergvliet and Prieska.
Purcell continued his education in Germany with a focus on the internal structure of arachnids. In 1894 Friedrich-Wilhelms-Universitaet awarded him the degree DPhil with a thesis entitled "Ueber den Bau der Phalangidenaugen" ("On the structure of the eyes in the "Phalangida"").
Purcell returned to South Africa in 1895 and donated his collections of South African "Coleoptera" (Families "Cicindelidae" and "Carabidae"), and European "Coleoptera" and "Rhynchota", to the South African Museum.
Career.
Purcell applied for the position of director of the South African Museum in 1895 following the resignation of Roland Trimen but did not get the post. He took up an appointment as First Assistant at the South African Museum and keeper of the terrestrial invertebrates collection (excluding insects) in 1896, under its new Director, W.L. Sclater. He kept this position until 1905 when he retired owing to poor health.
He initiated the systematic study of South African scorpions, including the description of many new species. In 1899 he provided the first description of local "Solifugae" (Camel spider or Sun spider) and collected a large number of specimens.
He was the first South African zoologist to start a systematic study of spiders, devising keys and providing full descriptions of species. Up to that time Arthur Stanley Hirst (1883–1930), Pickard-Cambridge and R. I. Pocock of the British Museum had occasionally named spiders sent to them from South African sources. Pocock especially was supplied with unknown specimens from Natal and Rhodesia, many coming from Selmar Schonland, the botany professor at Rhodes University.
South Africa is a fertile hunting ground for the study of Mygalomorphae or 4-lunged spiders, and both Purcell and R. W. E. Tucker who succeeded him, were drawn to this group, as was J. Hewitt. William and Anna Purcell are an example of husband and wife collaboration in arachnology, the other well-known couple being George and Elizabeth Peckham from the States who worked on South African Salticidae.
Purcell was the first zoologist in Africa to make a thorough study of "Peripatus". He continued the work of H.N. Moseley, A. Sedgwick and others and described one new genus and three new species.
Eponymns.
The standard author abbreviation Purcell is used to indicate this individual as the author when citing a zoological name.
Selected publications.
Purcell published mainly in "Annals of the South African Museum" and the "Transactions of the South African Philosophical Society". Some of his publications include:
Private life.
On 24 March 1897, Purcell married Anna Cambier Faure, who was a close South African friend of Olive Schreiner. The Purcell's had three children, Frederick Walter Faure Purcell, Olive Margaretha Deneys Purcell and William Frederick Hertzog Purcell. Anna Purcell was a cousin of Barry Hertzog, and her sister Joey married a Smuts. During the South African War (1899-1902) Anna was involved in relief work for Boer women and children. She later became involved in the Cape Women’s Enfranchisement League, of which Schreiner was a high profile member.
The Purcells lived on a country estate on the outskirts of Cape Town called Bergvliet. The farm was originally part of W.A. van der Stel's farm Groot Constantia.
In 1905 Purcell retired from the South African Museum owing to ill health, although he continued some of his work as honorary keeper at the South African Museum up until 1908. He retired to Bergvliet where he managed the farm on behalf of his family until his death in 1919. He continued to collect specimens of arachnids and insects but his main activity was to create an Herbarium of the farm's natural vegetation. The herbarium is preserved in the Compton Herbarium at the National Botanical Institute in Cape Town.
Purcell had a strong interest in Cape history, art and antiques and, with his and his wife's acquaintance with influential members of South African society, influenced the South African Museum in the purchase of the Koopmans-de Wet House, its conversion into a museum and his appointment as honorary curator.


Crossota millsae

Crossota millsae is a species of deep-sea hydrozoan. These small ocean-dwelling creatures are bioluminescent; the light emitted by these jellyfish serves as a defense or warning to other creatures. Males and females have both been described, and it reproduces sexually. They are viviparous and females brood baby medusae attached to the gastric canals inside the sub-umbrellar space.
Distribution.
"Crossota millsae" was first described from the Pacific Ocean off Hawaii and California. It was subsequently found in the Arctic Ocean and in Guayanilla Canyon off Puerto Rico. NOAA researchers who filmed this species in 2018 near Puerto Rico called it a "psychedelic" jellyfish. It lives below 1 km depth in all four regions. Its highest abundance is found at 2500 m off California and 1250 m off Hawaii. In the Arctic Ocean, it has been observed sitting on the seafloor.
Etymology.
It was named after Dr. Claudia Mills, a marine scientist at the Friday Harbor Laboratories.


Leucosolenida

Leucosolenida is an order of sponges in the class Calcarea. Species in the order Leucosolenida are calcareous with a skeleton composed exclusively of free spicules without calcified non-spicular reinforcements.
References.
http://species-identification.org/species.php?species_group=sponges&selected=beschrijving&menuentry=groepen&record=Leucosolenida


Metamale

A metamale (or supermale) is a low viability "Drosophila" fruit fly with a male phenotype in which the ratio of X chromosomes to sets of autosomes (A) is less than 0.5. For example: a fly with one X chromosome and two sets of autosomes is a normal male, a fly with one X chromosome and three sets of autosomes is a metamale.
American geneticist Calvin Bridges, who discovered the genic balance sex-determination system in "Drosophila" in 1921, used the terms "superfemale" and "supermale". German-American geneticist Curt Stern proposed the alternate terms "metafemale" and "metamale" in 1959.


Rokopella oligotropha

Rokopella oligotropha is a species of monoplacophoran, a superficially limpet-like marine mollusc. It is known from only one specimen and a shell fragment collected in the north-central Pacific Ocean.


Waap Entertainment

 is a Japanese adult video production company with headquarters in the Shinjuku Building, Shinjuku, Tokyo.
Company information.
Waap Entertainment was founded in 1998 and released its first videos in December of that year. The company specializes in single actress videos and is best known for its series which premiered on December 17, 1998 with "Dream Shower No.1" starring Izumi Maki and directed by Alala Kurosawa. The series is part bukkake and part gangbang and has appeared in more than sixty installments on the company's Beauty label. The studio is also recognized for having developed several prominent modern AV directors including Alala Kurosawa, [Jo]Style, K*WEST and KINGDOM.
When S1 No. 1 Style introduced the new less concealing digital mosaic style of censorship in late 2004, Waap followed soon afterward with their own videos. Waap Entertainment produces about 10 new videos per month and the Hokuto Corporation's AV retailer DMM listed more than 1500 DVD titles available under the Waap Entertainment name as of September 2011.
The company's reputation has extended to the Village Voice where columnist Johnny Maldoro named Waap's video "Semen Club 2" () starring Yui Kayama as the Bukkake Best of 2003. Waap has also expanded into another area of entertainment with game, puzzle and photo collection apps for the iPhone featuring some of the studio's top models.
Labels.
Waap has used a number of different labels for its videos since 1998:
Directors.
Prominent directors at Waap Entertainment include:
Actresses.
Popular AV Idols who have appeared in Waap Entertainment videos include:
Series.
Some popular Waap series:
AV Open / AV Grand Prix.
For the 2006 AV Open competition, Waap entered both the Main Stage and the Challenge stage. Their Main Stage entry was "Only One - Miracle Woman" (), video OPEN-0616, featuring several amateur actresses. In the Challenge Stage, the company nominated "Divide My Pleasure" () directed by Kirin, starring Ren Hitomi and Yuri Ueno, and labelled OPEN-0652.
Waap Entertainment was also one of the 19 companies which submitted entries for the 2007 AV Open contest. Their entry "Deep Lesbian & Hot Semen & Black Fuck" (), labelled OPEN-0717, was an interracial video starring Marin and Shiho, and directed by K*WEST. which finished in 8th place overall and won a Lily Franky Honorary President Prize.
The company was also one of the participants in the Hokuto Corporation sponsored 2008 AV Grand Prix with their entry "Shall We Fuck x10" (), AVGP-042, starring Lemon Tachibana and directed by K*WEST and Goemon. In the 2009 AV Grand Prix, Waap took one of the Special Awards Fetish Video for "Tsubomi - Semen Club" (), AVGP-148, with Tsubomi, directed by Takuan.


Archaellum

An archaellum (plural: "archaella", formerly archaeal flagellum) is a unique whip-like structure on the cell surface of many archaea. The name was proposed in 2012 following studies that showed it to be evolutionarily and structurally different from the bacterial and eukaryotic flagella. The archaellum is functionally the same – it can be rotated and is used to swim in liquid environments. The archaellum was found to be structurally similar to the type IV pilus.
History.
In 1977, archaea were first classified as a separate group of prokaryotes in the three-domain system of Carl Woese and George E. Fox, based on the differences in the sequence of ribosomal RNA (16S rRNA) genes. This domain possesses numerous fundamental traits distinct from both the bacterial and the eukaryotic domains. Many archaea possess a rotating motility structure that at first seemed to resemble the bacterial and eukaryotic flagella. The flagellum (Latin for whip) is a lash-like appendage that protrudes from the cell. In the last two decades, it was discovered that the archaeal flagella, although functionally similar to bacterial and eukaryotic flagella, structurally resemble bacterial type IV pili. Bacterial type IV pili are surface structures that can be extended and retracted to give a twitching motility and are used to adhere to or move on solid surfaces; their "tail" proteins are called pilins. To underline these differences, Ken Jarrell and Sonja-Verena Albers proposed to change the name of the archaeal flagellum to archaellum.
Structure.
Components.
Most proteins that make up the archaellum are encoded within one genetic locus. This genetic locus contains 7-13 genes which encode proteins involved in either assembly or function of the archaellum. The genetic locus contains genes encoding archaellins ("flaA" and "flaB") - the structural components of the filament - and motor components ("flaI", "flaJ", "flaH"). The locus furthermore encodes other accessory proteins ("flaG", "flaF", "flaC", "flaD", "flaE", and "flaX"). FlaX is only found in Crenarchaeota and FlaCDE (which can exist as individual proteins or as fusion proteins) in Euryarchaeotes. FlaX and FlaCDE are thought to have similar functions, and an unknown protein is also thought to fulfil the same function in Thaumarchaeota.
The archaellum operon used to be historically known as "fla" (from "flagellum"), but in order to avoid confusion with the bacterial flagellum and to be consistent with the remaining nomenclature (archaellum, archaellins), it has been recently proposed to be renamed to "arl" (archaellin-related genes). Consequently, the name of the genes is also different (e.g., "flaJ" is now "arlJ"). Therefore, in the specialised literature both nomenclatures can be found, with the "arl" nomenclature being increasingly more used since 2018.
Genetic analysis in different archaea revealed that each of these components is essential for assembly of the archaellum. Whereas most of the fla-associated genes are generally found in Euryarchaeota, one or more of these genes are absent from the fla-operon in Crenarchaeota. The prepilin peptidase (called PibD in crenarchaeota and FlaK in euryarchaeota) is essential for the maturation of the archaellins and is generally encoded elsewhere on the chromosome.
Functional characterization has been performed for ArlI, a Type II/IV secretion system ATPase super-family member and PibD/FlaK. FlaI forms a hexamer which hydrolyses ATP and most likely generates energy to assemble the archaellum and to power its rotation. PibD cleaves the N-terminus of the archaellins before they can be assembled. ArlH () has a RecA-like fold and inactive ATPase domains. ArlH and ArlJ are the two other core components that together with ArlI form a core platform/motor. ArlX acts as a scaffold around the motor in Crenarchaeota. ArlF and ArlG are potentially part of the stator of the archaellum motor; ArlF binds the S-layer, and ArlG forms filaments that seem to be "capped" by ArlF. Therefore, these two proteins potentially act together to attach the motor complex to the S-layer and to provide a rigid structure against which the rotating components of the motor - likely ArlJ - can rotate.
The genes coding for "arlC", "arlD", and "arlE" are only present in Euryarchaeota and interact with chemotaxis proteins (e.g., CheY, CheD and CheC2, and the archaea-specific CheF) to sense environmental signals (such as exposure to light of specific wavelength, nutrient conditions etc.).
Structure and assembly: type IV pilus (T4P) and archaellum.
In the 1980s, Dieter Oesterhelt’s laboratory showed for the first time that haloarchaea switch the rotation of their archaellum from clockwise to counterclockwise upon blue light pulses. This led microbiologists to believe that the archaeal motility structure is not only functionally, but also structurally reminiscent of bacterial flagella. Nevertheless, evidence started to build up indicating that archaella and flagella shared their function, but not their structure and evolutionary history. For example, in contrast to flagellins, archaellins (the protein monomers which form the archaellum filament) are produced as preproteins which are processed by a specific peptidase prior to assembly. Their signal peptide is homologous to class III signal peptides of type IV prepilins that are processed in Gram-negative bacteria by the peptidase PilD. In Crenarchaeota PibD and in euryarchaeota FlaK are PilD homologs, which are essential for the maturation of the archaellins. Furthermore, archaellins are N-glycosylated which has not been described for bacterial flagellins, where O-linked glycosylation is evident.
Another stark difference between the archaellum and the flagellum is the diameter of their filaments. While the bacterial flagellum is hollow, which allows flagellin monomers to travel through its interior to the tip of the growing filament, the archaellum filament is thinner, precluding the passage of archaellin monomers. This evidence suggested that the mechanism of assembly of the archaellum is more similar to the assembly mechanism observed in type IV pili (in which the monomers assemble at the bottom of the growing filament) than the assembly mechanism of flagella via a type III secretion system.
The similarities between archaella and T4P became more obvious with the identification of two archaella motor complex proteins that have homologues in T4P and type IV and II secretion systems. Specifically, ArlJ and ArlI are homologous to PilC and PilB/PilT, respectively. ArlJ is a membrane proteins for which little is structurally and functionally known, and ArlI is the only ATPase found in the archaellum operon, thus suggesting that this protein powers the assembly and the rotation of the filament.
Functional analogs.
Despite the limited number of details presently available regarding the structure and assembly of archaellum, it has become increasingly evident from multiple studies that archaella play important roles in a variety of cellular processes in archaea. In spite of the structural dissimilarities with the bacterial flagellum, the main function thus far attributed for archaellum is swimming in liquid and semi-solid surfaces. Increasing biochemical and biophysical information has further consolidated the early observations of archaella mediated swimming in archaea. Like the bacterial flagellum, the archaellum also mediates surface attachment and cell-cell communication. However, unlike the bacterial flagellum archaellum has not shown to play a role in archaeal biofilm formation. In archaeal biofilms, the only proposed function is thus far during the dispersal phase of biofilm when archaeal cells escape the community using their archaellum to further initiate the next round of biofilm formation. Also, archaellum have been found to be able to have a metal-binding site.


Tithonoceras

Tithonoceras is a genus of nautiloid cephalopod from the Upper Jurassic (Thithonian stage) found in the Crimea, belonging to the nautilacean family Paracenoceratidae.
The shell of "Tithonoceras" is evolute, coiled with all whorls exposed, smooth, and laterally compressed. The whorl section is subquadrangular with a broad, flattened venter on the outer rim. Ventrolateral shoulders are inflated, forming broad, rounded, keels, bordered by broad furrows on the flanks. The suture is sinuous, with ventral and lateral lobes. The position of the siphuncle is unknown.


Tit-tyrant

The tit-tyrants are a group of small, mainly Andean, tyrant flycatchers found in the genera Anairetes and Uromyias.
The tit-tyrants are fairly small birds (11–14 cm) that get their common name from the tit family, due to their energetic tit-like dispositions and appearance, primarily in their crests. Tit-tyrants live in temperate or arid scrub habitats and are mainly found in the Andes mountains. It is one of only a few genera of small flycatchers that occur at such high altitudes.