Sponge
Sponges (also known as sea sponges), the members of the phylum Porifera[3] (/pəˈrɪfərəˌ pɔː-/ pər-IF-ər-ə, por-; meaning 'pore bearer'),[4] are a basal animal clade as a sister of the diploblasts.[5][6][7][8][9] They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through them, consisting of jelly-like mesohyl sandwiched between two thin layers of cells.
This article is about the phylum of aquatic animal. For the porous cleaning tool, see Sponge (tool). For other uses, see Sponge (disambiguation).
Sponges have unspecialized cells that can transform into other types and that often migrate between the main cell layers and the mesohyl in the process. Sponges do not have complex nervous,[10] digestive or circulatory systems like humans. Instead, most rely on maintaining a constant water flow through their bodies to obtain food and oxygen and to remove wastes. Believed to be some of the most basal animals alive today, sponges were possibly the first to branch off the evolutionary tree from the last common ancestor of all animals, which would make them the sister group of all other animals.[5]
The branch of zoology that studies sponges is known as spongiology.[11]
Etymology
The term sponge derives from the Ancient Greek word σπόγγος spóngos.[12]
Systematics
Taxonomy
Carl Linnaeus, who classified most kinds of sessile animals as belonging to the order Zoophyta in the class Vermes, mistakenly identified the genus Spongia as plants in the order Algae.[82] For a long time thereafter, sponges were assigned to subkingdom Parazoa ("beside the animals") separated from the Eumetazoa which formed the rest of the kingdom Animalia.[83] They have been regarded as a paraphyletic phylum, from which the higher animals have evolved.[84] Other research indicates Porifera is monophyletic.[85]
The phylum Porifera is further divided into classes mainly according to the composition of their skeletons:[20][32]