Poriferans are “sponges.” They are among the oldest known animal fossils, dating from the Late Precambrian. The fossil record exceeds 900 genera. There are about 5,000 living sponge species in three distinct groups: Demospongia (soft sponges), Hexactinellida (glass sponges), and Calcarea (calcareous sponges). Sponges are filter feeders. Sponges have tiny pores in their outer walls through which water is drawn in. Cells within sponge walls filter plankton from the water pumped through the body and out other larger openings.
|Examples of Sponges|
|Figure 15.5. Branching tube sponge (soft sponge)||Figure 15.6. Barrel sponge
|Figure 15.7. Calcareous sponge||Figure 15.8. Glass sponge|