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simple organisms and echinoderms
Living beings formed of one or more cells, some of which possess a skeleton formed of calcareous spicules.
animal cell
Smallest living structure and constituent unit of all animals, including human beings; its size and shape vary according to function.
sponge
Porous multicell organism, mostly marine (currently about 5,000 species); it anchors itself to a support and filters water to take in food particles.
unicellulars
Single-cell organisms living in freshwater or salt water, in humid soil or as parasites of other organisms (plants or animals).
