Sponge

Sponges or sea sponges are primarily marine invertebrates of the animal phylum Porifera (; meaning 'pore bearer'). They are filter feeders that are typically bound to the seabed, being sessile. Sponges are one of the most ancient members of living seabed community (macrobenthos), with many species being important reef-builders. Some sponge species inhabit freshwater. Sponges are multicellular organisms consisting of jelly-like mesohyl sandwiched between two thin layers of cells, and usually have tube-like bodies full of pores and channels that allow water to circulate through them. They have unspecialized cells that can transform into other types and that often migrate between the main cell layers and the mesohyl in the process. They do not have complex nervous, digestive or circulatory systems. Instead, most sponges rely on maintaining a constant water flow through their bodies to obtain food and oxygen and to remove waste products, usually via flagellar movements of the so-called "collar cells". Sponges may be the sister group to all other animals, although the evidence for this relationship remains inconclusive, and different studies may recover different placements between sponges and other animal clades. Fossil evidence of primitive sponges such as Otavia dates to as early as the Tonian period (around 800 Mya). The branch of zoology that studies sponges is spongiology. Historically, the skeletons of sea sponges were used as the cleaning tool of the same name, though this is no longer a common practice.