Regispongia Sponge fossils.jpg
Regispongia Sponge fossils
Bangor Limestone Formation in north Alabama
Mississippian Period (ca 325,0000,000 yrs old)
Sponges, the members of the phylum Porifera (meaning "pore bearer"), are the basalmost clade of animals, as sister of the diploblasts. They are multicellular parazoan 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. 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 nervous, digestive or circulatory systems. Instead, most rely on maintaining a constant water flow through their bodies to obtain food and oxygen and to remove wastes.