ABSTRACT
Reported first from Chile as branchiobdellid leeches (Moquin-Tandon 1846), then from the Philippines as monogeneans (Semper 1872), these little ectosymbiotic worms found mainly on freshwater crustaceans were first recognized to have turbellarian affinities by van Beneden (1876). Though formally placed in the Platyhelminthes by Benham (1901), their affinities were uncertain: Haswell (1893), Hett (1925) and Borradaile et al. (1948), for example, all assigned them to the trematodes. More recently, while recognizing them as unquestionably related to the rhabdocoel turbellarians, Ehlers (1985a) was unable to provide a clear apomorphy for the group. We now accept the presence of an epidermis made of multiple syncytial plates first reported by Williams (1975) as a uniquely temnocephalan character (see Joffe and Cannon 1998a).
