Mk. Litvaitis et K. Rohde, A molecular test of platyhelminth phylogeny: inferences from partial 28S rDNA sequences, INVERTEBR B, 118(1), 1999, pp. 42-56
Nucleotide sequences of the region extending from the D3 to the D6 expansio
n segments of the 28S rDNA gene were used to reconstruct evolutionary relat
ionships within the Platyhelminthes. Neighbor-joining and parsimony analyse
s of representatives of most major platyhelminth taxa revealed a basal Cate
nulida, a monophyletic Acoelomorpha, a sister-group relationship of Macrost
omorpha and Polycladida (59% of bootstrap replications), and monophyletic T
ricladida. We found no evidence of a taxon Seriata (p=.0001); however, the
paraphyletic status of the Proseriata needs further investigation. Although
Neodermata appeared as a monophyletic group, Monogenea was paraphyletic (p
<.0001), thus not supporting the taxon Cercomeromorpha. Monopisthocotylean
Monogenea was the most basal taxon among the Neodermata, and Udonella sp. c
onsistently grouped with the Monopisthocotylea. Other relationships within
the Neodermata showed Trematoda as a monophyletic taxon and, among its memb
ers, Rugogaster hydrolagi was identified as an aspidogastrean. The taxa Ces
todaria (Amphilinidae and Gyrocotylidae) and Eucestoda were both supported;
however, constraining these 2 clades into a monophyletic Cestoda resulted
in a significantly longer tree (p=.0303). We tentatively conclude that the
immediate sister group of Neodermata is Fecampiida. But because of contradi
ctory results of the constraint analyses, we cannot exclude the possibility
that the sister group to Neodermata is a taxon containing many neoophoran
turbellarians (e.g., Rhabdocoela and Tricladida).