protist locomotion protist locomotion protists are the eukaryotes that cannot be classified as plants, fungi or animals. they are mostly unicellular and microscopic. many unicellular protists, particularly protozoans, are motile and can generate movement using flagella, cilia or pseudopods. cells which use flagella for movement are usually referred to as flagellates, cells which use cilia are usually referred to as ciliates, and cells which use pseudopods are usually referred to as amoeba or amoeboids. other protists are not motile, and consequently have no built-in movement mechanism. part of a series onmicrobial and microbot movement microswimmers taxa bacterial motility run-and-tumble twitching gliding protist locomotion amoeboids taxis aerotaxis (oxygen) anemotaxis (wind) chemotaxis (chemicals) electrotaxis(electric current) gravitaxis (gravity) magnetotaxis (magnetic field) phototaxis (light) rheotaxis (fluid flow) thermotaxis (temperature) kinesis kinesis chemokinesis photokinesis microbots and particles microbotics nanorobotics nanomotors dna machine microparticle nanoparticle janus particles self-propelled particles swarm robotics biohybrids biohybrid microswimmers bacterial biohybrids protist biohybrids robotic sperm collective motion active matter bacteria collective motion collective cell migration quorum sensing swarming motility molecular motors biological motors flagellum archaellum cilium axoneme motor switch intraflagellar evolution motor proteins myosin kinesin dynein synthetic motors synthetic molecular motor molecular modelling molecular propeller molecular sensor molecular shuttle molecular tweezers related brownian motor biochip endocytosis axophilic migration cytoskeleton prokaryotic eukaryotic cytoplasmic streaming gray goo mucilage molecular biophysics molecular machine nanoengineering non-motile bacteria virophysics category overview some motile unicellular protists unicellular protists comprise a vast, diverse group of organisms that covers virtually all environments and habitats, displaying a menagerie of shapes and forms. hundreds of species of the ciliate genus paramecium or flagellated euglena are found in marine, brackish, and freshwater reservoirs; the green algae chlamydomonas is distributed in soil and fresh water world-wide; parasites from the genus giardia colonize intestines of several vertebrate species. one of the shared features of these organisms is their motility, crucial for nutrient acquisition and avoidance of danger. in the process of evolution, single-celled organisms have developed in a variety of directions, and thus their rich morphology results in a large spectrum of swimming modes. many swimming protists actuate tail-like appendages called flagella or cilia in order to generate the required thrust. this is achieved by actively generating deformations along the flagellum, giving rise to a complex waveform. the flagellar axoneme itself is a bundle of nine pairs of microtubule doublets surrounding two central microtubules, termed the 9+2 axoneme, and cross-linking dynein motors, powered by atp hydrolysis, perform mechanical work by promoting the relative sliding of filaments, resulting in bending deformations. although protist flagella have a diversity of forms and functions, two large families, flagellates and ciliates, can be distinguished by the shape and beating pattern of their flagella. in the phylogenetic tree on the right, aquatic organisms (living in marine, brackish, or freshwater environments) have their branches drawn in blue while parasitic organisms have their branches drawn in red. ciliates are indicated by an asterisk after their names. for each phylum marked in bold font, a representative organism has been sketched next to its name. modes of locomotion protists according to how they move type of protist movement mechanism description example other examples motile flagellates a flagellum (latin for whip) is a lash-like appendage that protrudes from the cell body of some protists (as well as some bacteria). flagellates use from one to several flagella for locomotion and sometimes as feeding and sensory organelle. cryptophytes all dinoflagellates and nanoflagellates (choanoflagellates, silicoflagellates, most green algae)(other protists go through a phase as gametes when they have temporary flagellum – some radiolarians, foraminiferans and apicomplexa) ciliates a cilium (latin for eyelash) is a tiny flagellum. ciliates use multiple cilia, which can number in many hundreds, to power themselves through the water. paramecium bursariaclick to see cilia foraminiferans, and some marine amoebae, ciliates and flagellates. amoebas(amoeboids) pseudopods (greek for false feet) are lobe-like appendages which amoebas use to anchor to a solid surface and pull themselves forward. they can change their shape by extending and retracting these pseudopods. amoeba found in every major protist lineage. amoeboid cells occur among the protozoans, but also in the algae and the fungi. not motile none diatom coccolithophores, most diatoms, and non‐motile species of phaeocystis among protozoans the parasitic apicomplexa are non‐motile. flagellates difference of beating pattern of flagellum and cilium flagella are used in prokaryotes (archaea and bacteria) as well as protists. in addition, both flagella and cilia are widely used in eukaryotic cells (plant and animal) apart from protists. the regular beat patterns of eukaryotic cilia and flagella generates motion on a cellular level. examples range from the propulsion of single cells such as the swimming of spermatozoa to the transport of fluid along a stationary layer of cells such as in a respiratory tract. though eukaryotic flagella and motile cilia are ultrastructurally identical, the beating pattern of the two organelles can be different. in the case of flagella, the motion is often planar and wave-like, whereas the motile cilia often perform a more complicated three-dimensional motion with a power and recovery stroke. eukaryotic flagella—those of animal, plant, and protist cells—are complex cellular projections that lash back and forth. eukaryotic flagella are classed along with eukaryotic motile cilia as undulipodia to emphasize their distinctive wavy appendage role in cellular function or motility. primary cilia are immotile, and are not undulipodia. marine flagellates from the genera (left to right)cryptaulax, abollifer, bodo, rhynchomonas, kittoksia, allas, and metromonas freshwater green algal flagellate (chlamydomonas) flagellates typically have a small number of long flagella distributed along the bodies, and they actuate them to generate thrust. the set of observed movement sequences includes planar undulatory waves and traveling helical waves, either from the base to the tip, or in the opposite direction. flagella attached to the same body might follow different beating patterns, leading to a complex locomotion strategy that often relies also on the resistance the cell body poses to the fluid. ciliates cilia performs powerful forward strokes with a stiffened flagellum followed by relatively slow recovery movement with a relaxed flagellum in contrast to flagellates, propulsion of ciliates derives from the motion of a layer of densely-packed and collectively-moving cilia, which are short hair-like flagella covering their bodies. the seminal review paper of brennen and winet (1977) lists a few examples from both groups, highlighting their shape, beat form, geometric characteristics and swimming properties. cilia may also be used for transport of the surrounding fluid, and their cooperativity can lead to directed flow generation. in higher organisms this can be crucial for internal transport processes, as in cytoplasmic streaming within plant cells, or the transport of ova from the ovary to the uterus in female mammals. ciliates generally have hundreds to thousands of cilia that are densely packed together in arrays. like the flagella, the cilia are powered by specialised molecular motors. an efficient forward stroke is made with a stiffened flagellum, followed by an inefficient backward stroke made with a relaxed flagellum. during movement, an individual cilium deforms as it uses the high-friction power strokes and the low-friction recovery strokes. since there are multiple cilia packed together on an individual organism, they display collective behaviour in a metachronal rhythm. this means the deformation of one cilium is in phase with the deformation of its neighbor, causing deformation waves that propagate along the surface of the organism. these propagating waves of cilia are what allow the organism to use the cilia in a coordinated manner to move. a typical example of a ciliated microorganism is the paramecium, a one-celled, ciliated protozoan covered by thousands of cilia. the cilia beating together allow the paramecium to propel through the water at speeds of 500 micrometers per second. cilia beating in a multi-ciliated microswimmer two images at different times, one just after the other, showing different dispositions of the beating cilia. the varying cilium color indicates the instantaneous stage in the beat cycle. the motion of the swimmer is from left to right paramecium feeding on bacteria the ciliate oxytricha trifallax with cilia clearly visible external video paramecium: the white rat of ciliates flinching saves lives in the microcosmos – journey to the microcosmos microbes in slow motion – journey to the microcosmos amoebas locomotion by pseudopodamoeba proteus with many pseudopodia