Sponges
Poriferans are commonly referred to as sponges. An early branching event in the history of animals separated the sponges from other metazoans. As one would expect based on their phylogenetic position, fossil sponges are among the oldest known animal fossils, dating from the Late Precambrian. Since then, sponges have been conspicuous members of many fossil communities; the number of described fossil genera exceeds 900. The approximately 5,000 living sponge species are classified in the phylum Porifera, which is composed of three distinct groups, the Hexactinellida (glass sponges), the Demospongia, and the Calcarea (calcareous sponges)


Anatomy of sponges








