ciliated cell collar cell A cell with a flagellum surrounded by a collar of microvilli. The motion of the flagellum draws water past the microvilli, serving either a feeding or sensory function. Collar cells are found in multiple animals, including sponges, echinoderms, and cnidarians. They are also found outside animals in the choanoflagellates. Although collar cells are superficially similar, their cytoskeletal structure and functional biology are different in different groups of organisms.