Choanocytes or collar cells are characteristic feature of members of phylum-Porifera as in sponges. These cells form endodermis of sponge. Each cells bears a contractile collar at the free end which encircles a single flagellum. Movement of water current takes place by movement of this flagellum. These cells help in food capturing and intracellular digestion in sponges. Phylum-Arthropoda is characterised by jointed legs. Phylum-Annelida is characterised by metamerism.