Contributions to the phylogeny of Platyhelminthes based on partial sequencing of 18S ribosomal DNA

Abstract

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 test several hypotheses concerning the phylogenetic relationships of Platyhelminthes. The following conclusions were reached: the Neodermata is monophyletic; Trematoda (Aspidogastrea and Digenea) is monophyletic, although a sister group relationship of the Aspidogastrea and all other Neodermata cannot be definitely ruled out; the Cestoda comprising the Eucestoda, Amphilinidea and Gyrocotylidea is monophyletic; it is unresolved whether the Monogenea is paraphyletic; neither Gyrocotylidea and Monopisthocotylea nor Gyrocotylidea and Monogenea as a whole are sister groups; Anoplodiscus is a monopisthocotylean monogenean; none of Proseriata, Pterastericolidae/Umagillidae, Kalyptorhynchia, Rhabdocoela as a whole, Dalyelliida or the Temnocephalidae is the sister group of the Neodermata; there is some evidence that a larger taxon consisting of Proseriata, Tricladida and Rhabdocoela may be the sister group of the Neodermata but definitive evidence for a sister group relationship between the Neodermata and any turbellarian taxon is lacking; Rhabdocoela and Lecithoepitheliata are not closely related; it is unresolved whether the Rhabdocoela is monophyletic; Umagillidae, Pterastericolidae and Temnocephalidae belong to one monophylum; the Temnocephalidae are very close to the dalyelliids; Tricladida and Rhabdocoela are sister groups, the exact position of the Catenulida and Nemertini in relation to the Platyhelminthes has not been resolved, although Catenulida and Lecithoepitheliata may belong to one clade.