Prolecithophora

All prolecithophorans are aquatic, with most living in the oceans. Some species, especially those living in freshwater, are predators and scavengers, but many marine species are associated with colonial animals such as bryozoans or live as symbionts on larger animals such as urchins; a few species harbor symbiotic algae. Although most are accomplished swimmers, they normally rarely venture far from the bottom; young specimens are sometimes found in plankton. Many species display positive or negative phototaxis. == Distribution ==

The majority of prolecithophorans live in the oceans. There are also brackish and freshwater species; in Lake Baikal, an adaptive radiation has resulted in a number of endemic species. The order has a cosmopolitan distribution; most described species are from temperate waters, while little is known about tropical or deep-sea species. This is probably due to a sampling artefact, as prolecithophorans are known to be common in the tropics; when Norén & Jondelius sampled the shore adjacent to Phuket Marine Biological Center, Phuket, Thailand, they found 14 species of prolecithophorans, all of which were new to science. == Families ==

The following families are recognised in the order Prolecithophora: • Multipeniatidae Karling, 1940 • Multipeniata Nasonov, 1927 • Plagiostomidae - mainly marine, a few freshwater species (e.g. Vänern, Lake Biwa and Lake Tanganyika) • Acmostomum Schmarda, 1859 • Auriculifera Kulinitch, 1973 • Hydrolimax Haldeman, 1842 • Plagiostomum Schmidt, 1852 • Plicastoma Graff, 1904 • Puzostoma Marcus, 1950 • Torgea Jondelius, 1997 • Tuilica Marcus, 1951 • Vorticeros Schmidt, 1852 • Protomonotresidae Reisinger, 1924 - exclusively freshwater species from Lake Baikal, with one exception • Baicalarctiinae Friedman, 1933 • Baicalarctia Friedmann, 1926 • Friedmaniella Timoshkin & Zabrovskaya, 1985 • Porfirievia Timoshkin, 1997 • Protomonotresinae Timoshkin, 1986 • Acanthiella Rieger & Sterrer, 1975 • Archimonotresis Meixner, 1938 • Prorogonophora Riedl, 1954 • Protomonotresis Reisinger, 1924 • Pseudostomidae Graff, 1904-08 - exclusively marine species • Allostoma Beneden, 1861 • Cylindrostoma Ørsted, 1845 • Einarhelmins Karling, 1993 • Enterostomula Reisinger, 1926 • Euxinia Graff, 1911 • Gonostomula Westblad, 1955 • Monoophorum Bohmig, 1890 • Pregermarium Stirewalt, Ferguson & Kepner, 1942 • Pseudostomum Schmidt, 1848 • Reisingeria Westblad, 1955 • Thallagus Marcus, 1951 • Ulianinia Levinsen, 1879 • Scleraulophoridae Marcus, 1950 • Rosmarium Marcus, 1950 • Scleraulophorus Karling, 1940 • Urostomatidae == References ==