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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, [ 50 ] mostly multicellular and including many notable seaweeds.
Microorganisms make up about 70% of the marine biomass. [4] A microorganism, or microbe, is a microscopic organism too small to be recognised adequately with the naked eye. In practice, that includes organisms smaller than about 0.1 mm. [12]: 13
Unlike plants, fungi and most types of algae, most protozoa do not have a rigid external cell wall but are usually enveloped by elastic structures of membranes that permit movement of the cell. In some protozoa, such as the ciliates and euglenozoans , the outer membrane of the cell is supported by a cytoskeletal infrastructure, which may be ...
In a reversal of the pattern on land, in the oceans, almost all photosynthesis is performed by algae and cyanobacteria, with a small fraction contributed by vascular plants and other groups. Algae encompass a diverse range of organisms, ranging from single floating cells to attached seaweeds. They include photoautotrophs from a variety of groups.
The 16-cell Gonium colony shown in the diagram on the right is organized into two concentric squares of respectively 4 and 12 cells, each biflagellated, held together by an extracellular matrix. [51] All flagella point out on the same side: It exhibits a much lower symmetry than Volvox, lacking anterior-posterior symmetry.
Diagram of a ciliate. A cytostome (from cyto-, cell and stome-, mouth) or cell mouth is a part of a cell specialized for phagocytosis, usually in the form of a microtubule-supported funnel or groove. Food is directed into the cytostome, and sealed into vacuoles. Only certain groups of protozoa, such as the Ciliophora and Excavata, have ...
Algae ranges from single floating cells to attached seaweeds, while vascular plants are represented in the ocean by groups such as the seagrasses and the mangroves. Larger producers, such as seagrasses and seaweeds , are mostly confined to the littoral zone and shallow waters, where they attach to the underlying substrate and are still within ...
Some cells in other animals may be flagellate, for instance the spermatozoa of most animal phyla. Flowering plants do not produce flagellate cells, but ferns, mosses, green algae, and some gymnosperms and closely related plants do so. [2] Likewise, most fungi do not produce cells with flagellae, but the primitive fungal chytrids do. [3]