The Phylum Porifera includes the animals commonly known as sponges. This is a diverse group, with about 5000 known species. Most are marine, but around 150 species live in fresh water. Considered the simplest of the animals, the cells of sponges are organized into tissues, but the tissues are not organized into organs. Their bodies are a sort of loose aggregation of different kinds of cells. Sponges are characterized by a unique feeding system involving a system of pores and canals through which water passes. The four Classes of sponges are Calcarea (Calcispongiae), Hexactinellida (Hyalospongiae), Demospongiae, and Sclerospongiae (considered by many to be a subclass of Demospongiae).- Category ID : 418449