CONTRIBUTIONS TO THE PHYLOGENY OF PLATYHELMINTHES BASED ON PARTIAL SEQUENCING OF 18S RIBOSOMAL DNA

Partial sequencing of the 18S ribosomal DNA gene of one nemertean and 13 free-living and parasitic Platyhelminthes (556 nucleotides), and of one nemertean and 20 Platyhelminthes (556 nucleotides) was used to te st several hypotheses concerning the phylogenetic relationships of Pla tyhelminthes. The following conclusions were reached: the Neodermata i s monophyletic; Trematoda (Aspidogastrea and Digenea) is monophyletic, although a sister group relationship of the Aspidogastrea and all oth er Neodermata cannot be definitely ruled out; the Cestoda comprising t he Eucestoda, Amphilinidea and Gyrocotylidea is monophyletic; it is un resolved whether the Monogenea is paraphyletic; neither Gyrocotylidea and Monopisthocotylea nor Gyrocotylidea and Monogenea as a whole are s ister groups; Anoplodiscus is a monopisthocotylean monogenean; none of Proseriata, Pterastericolidae/Umagillidae, Kalyptorhynchia, Rhabdocoe la as a whole, Dalyelliida or the Temnocephalidae is the sister group of the Neodermata; there is some evidence that a larger taxon consisti ng of Proseriata, Tricladida and Rhabdocoela may be the sister group o f the Neodermata but definitive evidence for a sister group relationsh ip between the Neodermata and any turbellarian taxon is lacking; Rhabd ocoela and Lecithoepitheliata are not closely related; it is unresolve d whether the Rhabdocoela is monophyletic; Umagillidae, Pterastericoli dae and Temnocephalidae belong to one monophylum; the Temnocephalidae are very close to the dalyelliids; Tricladida and Rhabdocoela are sist er groups, the exact position of the Catenulida and Nemertini in relat ion to the Platyhelminthes has not been resolved, although Catenulida and Lecithoepitheliata may belong to one clade.