Sponges …
- are among the least complex members of the animal kingdom;
- have no organs or tissues, though they do have many different kinds of cells;
- are built around a system of canals and chambers that allows them to filter large volumes of water;
- have unique collar cells with a flagellum that drives water through the canals and chambers, and can move up to ten times the sponge’s body volume of water in an hour;
- feed chiefly on particles the size of bacteria or smaller;
- digest their food within cells, not inside a body cavity such as a stomach;
- almost all produce a supportive mineral (silica or calcium carbonate) or organic (protein fiber) skeleton, or both;
- have separate sexes, or change sexes as they grow;
- can reproduce asexually through buds or fragments that can give rise to another individual;
- grow into a distinctive shape or vary widely depending upon factors such as currents, seafloor configuration or turbidity;
- mostly live in the ocean (a few live in freshwater), attached to the seafloor for most of their lives (although their larvae can crawl or swim);
- range in size from almost microscopic to over 3.5 meters across;
- harbor diverse communities of bacteria with which they maintain unique relationships that may involve mediating bacterial metabolisms, and carrying out processes such as photosynthesis or nitrification;
- probably number over 15,000 species (7,000 have been described scientifically);
- often require microscopic examination of skeletal structures for identification.