ABSTRACT
The taxon Prolecithophora was recognized by Karling (1940) in his doctoral dissertation, but the first species later to be assigned to the Prolecithophora was described as early as 1788 by O.E. Müller (Vorticeros auriculatum). Today, the taxon comprises about 150 known species classified conventionally in about a dozen families: Protomonotresidae, Pseudostomidae, Cylindrostomidae, Scleraulophoridae, Urastomidae, Genostomatidae (as Hypotrichinidae), Baicalarctiidae, Ulianinidae, Multipeniatidae and Plagiostomidae as recognized by Cannon (1986). Most recently the Torgeidae was described by Jondelius (1997). The approximately 150 known species belonging to the Prolecithophora are free-living; though found predominantly in marine habitats, they are known from freshwater. Most prolecithophorans live in soft sediments, sometimes interstitially or among plants. The Urastomidae and Genostomatidae are symbionts of bivalves, crustaceans, or fish, but may not be members of the Prolecithophora (Ehlers 1988; Hyra 1993; Watson 1997a).
