Sponge, any of the primitive multicellular aquatic animals that constitute the phylum Porifera. They number approximately 5,000 described species and inhabit all seas, where they occur attached to surfaces from the intertidal zone to depths of 8,500 metres (29,000 feet) or more.
Porifera are an ancient and highly successful group of animals. In the Palaeozoic, they are believed to have comprised more than half the biomass in marine reefs. They have been living in the waters of the world for more than 600 million years, and can now be found in all marine and many freshwater habitats. No definite symmetry.
Porifera is an early branching event in the history of animals and 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.
Porifera are all aquatic, mostly marine except one family Spongillidae which lives in freshwater. They are sessile and sedentary and grow like plants. The body shape is vase or cylinder-like, asymmetrical, or radially symmetrical.
Sponges are simple invertebrate animals that live in aquatic habitats. Although the majority of sponges are marine, some species live in freshwater lakes and streams. They are found in shallow ocean environments to depths as great as five kilometers (km).
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).
Sponges are members of the phylum Porifera, which contains the simplest invertebrates. (credit: Andrew Turner) There are at least 5,000 named species of sponges, likely with thousands more yet to be classified.