Explanation

Sponges are the simplest multicellular animals and are placed in the phylum Porifera (pore-bearers), whose bodies are perforated by pores through which water circulates. Platyhelminthes are flatworms, Cnidaria includes jellyfish and corals, and Annelida are the segmented worms. Water enters through tiny pores (ostia) and exits through a large opening (osculum), filtering food particles on the way.