ASPECTS OF THE PHYLOGENY OF PLATYHELMINTHES BASED ON 18S RIBOSOMAL DNA AND PROTONEPHRIDIAL ULTRASTRUCTURE

DNA studies of 23 taxa (20 platyhelminths, 1 nemertean, Home and Artem ia) and electron-microscopic studies of the protonephridia of many pla tyhelminths (supported by some additional ultrastructural data) have l ed to the following conclusions: the Neodermata are monophyletic; Temn ocephalida and Dalyelliida form one clade and are not the 'primitive' sister group of the Neodermata; Gyrocotylidea, Amphilinidea and Eucest oda form one monophylum; Pterastericolidae and Umagillidae are dalyell iids and not the sister group of the Neodermata; and Proseriata are un likely to be closely related with the Tricladida. A large taxon consis ting of the Proseriata and some other 'turbellarians' may represent th e sister group of the Neodermata.