are immotile, and are not undulipodia. marine flagellates from the genera (left to right)cryptaulax, abollifer, bodo, rhynchomonas, kiitoksia, allas, and metromonas cilia performs powerful forward strokes with a stiffened flagellum followed by relatively slow recovery movement with a relaxed flagellum 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. flagellate, ciliates and amoeba green algal flagellate (chlamydomonas) paramecium feeding on bacteria the ciliate oxytricha trifallax with cilia clearly visible amoeba with ingested diatoms external video paramecium: the white rat of ciliates marine algae part of a series onplankton trophic mode phytoplankton zooplankton mixoplankton mycoplankton bacterioplankton virioplankton by size heterotrophic picoplankton microalgae microzooplankton nanophytoplankton calcareous photosynthetic picoplankton picoeukaryote picoplankton marine microplankton by taxonomy algae diatoms coccolithophores dinoflagellates protozoans radiolarians foraminiferans amoebae ciliates bacteria cyanobacteria archaea viruses by habitat aeroplankton geoplankton marine plankton prokaryotes protists freshwater plankton other types gelatinous zooplankton holoplankton ichthyoplankton meroplankton pseudoplankton tychoplankton blooms algal bloom critical depth cyanobacterial bloom harmful algal bloom spring bloom eutrophication great atlantic sargassum belt great calcite belt milky seas effect related topics algaculture claw hypothesis cpr diel vertical migration f-ratio marine primary production ocean fertilization iron paradox of the plankton planktivore planktology thin layers naames category algae is an informal term for a widespread and diverse group of photosynthetic protists which are not necessarily closely related and are thus polyphyletic. marine algae can be divided into six groups: green, red and brown algae, euglenophytes, dinoflagellates and diatoms. dinoflagellates and diatoms are important components of marine algae and have their own sections below. euglenophytes are a phylum of unicellular flagellates with only a few marine members. not all algae are microscopic. green, red and brown algae all have multicellular macroscopic forms that make up the familiar seaweeds. green algae, an informal group, contains about 8,000 recognised species. many species live most of their lives as single cells or are filamentous, while others form colonies made up from long chains of cells, or are highly differentiated macroscopic seaweeds. red algae, a (disputed) phylum contains about 7,000 recognised species, mostly multicellular and including many notable seaweeds. brown algae form a class containing about 2,000 recognised species, mostly multicellular and including many seaweeds such as kelp. unlike higher plants, algae lack roots, stems, or leaves. they can be classified by size as microalgae or macroalgae. microalgae are the microscopic types of algae, not visible to the naked eye. they are mostly unicellular species which exist as individuals or in chains or groups, though some are multicellular. microalgae are important components of the marine protists discussed above, as well as the phytoplankton discussed below. they are very diverse. it has been estimated there are 200,000-800,000 species of which about 50,000 species have been described. depending on the species, their sizes range from a few micrometers (µm) to a few hundred micrometers. they are specially adapted to an environment dominated by viscous forces. chlamydomonas globosa, a unicellular green alga with two flagella just visible at bottom left chlorella vulgaris, a common green microalgae, in endosymbiosis with a ciliate centric diatom dinoflagellates macroalgae are the larger, multicellular and more visible types of algae, commonly called seaweeds. seaweeds usually grow in shallow coastal waters where they are anchored to the seafloor by a holdfast. like microalgae, macroalgae (seaweeds) can be regarded as marine protists since they are not true plants. but they are not microorganisms, so they are not within the scope of this article. unicellular organisms are usually microscopic, less than one tenth of a millimeter long. there are exceptions. mermaid's wineglass, a genus of subtropical green algae, is single-celled but remarkably large and complex in form with a single large nucleus, making it a model organism for studying cell biology. another single-celled algae, caulerpa taxifolia, has the appearance of a vascular plant including "leaves" arranged neatly up stalks like a fern. selective breeding in aquariums to produce hardier strains resulted in an accidental release into the mediterranean where it has become an invasive species known colloquially as killer algae. diatoms diatoms come in many shapes and sizes diatoms are photosynthetic unicellular algae populating the oceans and other waters around the globe. they form a (disputed) phylum containing about 100,000 recognised species. diatoms generate about 20 percent of all oxygen produced on the planet each year, and take in over 6.7 billion metric tons of silicon each year from the waters in which they live. they produce 25–45% of the total primary production of organic material in the oceans, owing to their prevalence in open-ocean regions when total phytoplankton biomass is maximal. diatoms are enclosed in protective silica (glass) shells called frustules. they are classified by the shape of these glass cages in which they live, and which they build as they grow. each frustule is made from two interlocking parts covered with tiny holes through which the diatom exchanges nutrients and wastes. dead diatoms drift to the ocean floor where, over millions of years, the remains of their frustules can build up as much as half a mile deep. diatoms have relatively high sinking speeds compared with other phytoplankton groups, and they account for about 40% of particulate carbon exported to ocean depths. diatoms are one of the most common types of phytoplankton their protective shells (frustles) are made of silicon diatom shapes drawings by haeckel 1904 (click for details) diatomscentricpennatediatoms have a silica shell (frustule) with radial (centric) or bilateral (pennate) symmetry external video diatoms: tiny factories you can see from space diatom 3d interference contrast structure of a centric diatom frustule physically driven seasonal enrichments in surface nutrients favour diatom blooms. anthropogenic climate change will directly affect these seasonal cycles, changing the timing of blooms and diminishing their biomass, which will reduce primary production and co2 uptake. remote sensing data suggests there was a global decline of diatoms between 1998 and 2012, particularly in the north pacific, associated with shallowing of the surface mixed layer and lower nutrient concentrations. silicified frustule of a pennate diatom with two overlapping halves guinardia delicatula, a diatom responsible for diatom blooms in the north sea there are over 100,000 species of diatoms accounting for 25–45% of the ocean's primary production linked diatoms pennate diatom from an arctic meltpond, infected with two chytrid-like fungal pathogens. scale bar = 10 µm. coccolithophores coccolithophores...have plates called coccoliths...extinct fossilcoccolithophores build calcite skeletons important to the marine carbon cycle coccolithophores are minute unicellular photosynthetic protists with two flagella for locomotion. most of them are protected by calcium carbonate shells covered with ornate circular plates or scales called coccoliths. the term coccolithophore derives from the greek for a seed carrying stone, referring to their small size and the coccolith stones they carry. under the right conditions they bloom, like other phytoplankton, and can turn the ocean milky white. fossil of coccolithus pelagicus, about 10 μm acrossdiverse coccolithophores from the maldives the fossil coccolithophore braarudosphaera bigelowii has an unusual shell with a regular dodecahedral structure about 10 micrometers across. the coccolithophore emiliania huxleyi algae bloom of emiliania huxleyi off the southern coast of england coccolithophores named after the bbc documentary seriesthe blue planet dinoflagellates