Sponges are aquatic, mainly marine, multicellular animals. Sponges do not have real tissues and organs, and multiple individual cells and cell layers perform various functions. A significant part of the inner surface of sponges is lined with special cells with a flagellum and a collar of microvilli - choanocytes, which together constitute a choanoderm. Their body represents a porous system that is not present in cnidaria, roundworms, flatworms. All sponges are sessile aquatic animals and lack any organs for moving the body. In contrast to other animals, they do not have neurons and muscle fibres, as well as the digestive tract or digestive cavity. They filter water and feed on plankton and other microscopic marine organisms.
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