Filling a gap in the phylogeny of flatworms : relationships within the Rhabdocoela ( Platyhelminthes ) , inferred from 18 S ribosomal DNA sequences

1 Willems, W. R. , Wallberg A. , Jondelius, U. , Littlewood, D. T. J., Backeljau, T. , Schockaert, E. R. & Artois, T. J. (2006). Filling a gap in the phylogeny of flatworms: relationships within the Rhabdocoela (Platyhelminthes), inferred from 18S ribosomal DNA sequences. — Zoologica Scripta , 35 , 1–17. The phylogeny of the Rhabdocoela, a species-rich taxon of free-living flatworms, is reconstructed based on complete 18S rDNA sequences. The analysis includes 62 rhabdocoels and 102 representatives of all major flatworm taxa. In total, 46 new sequences are used, 41 of them from rhabdocoel species, five from proseriates. Phylogenetic analysis was performed using maximum parsimony and Bayesian inference. Clade support was evaluated with parsimony jackknifing, Bremer support indices and Bayesian posterior probabilities. The resulting cladogram corroborates that the Rhabdocoela is monophyletic, but its sister group remains uncertain. The ‘Dalyellioida’ and the ‘Typhloplanoida’, both former rhabdocoel subtaxa, are polyphyletic. Within the Rhabdocoela the monophyletic Kalyptorhynchia, characterized by a muscular proboscis, forms the sister group of all other rhabdocoels. The Schizorhynchia is a monophyletic subtaxon of the Kalyptorhynchia, with the split proboscis as a synapomorphy. Except for the Dalyelliidae and the Typhloplanidae, both freshwater taxa, none of the ‘families’ previously included in the ‘Typhloplanoida’ and the ‘Dalyellioida’ appears to be monophyletic. As a result of this analysis, three existing and four new taxon names are formally defined following the rules of the Phylocode. Wim R. Willems, Research Group Biodiversity, Phylogeny and Population Studies, Centre for Environmental Sciences, Hasselt University, Campus Diepenbeek, Agoralaan Building D, B-3590 Diepenbeek, Belgium. E-mail: wim.willems@uhasselt.be Andreas Wallberg, Systematic Zoology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18D, SE-752 36 Uppsala, Sweden. E-mail: andreas.wallberg@ebc.uu. se Ulf Jondelius, Systematic Zoology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18D, SE-752 36 Uppsala, Sweden. E-mail: ulf.jondelius@ebc.uu. se David T. J. Littlewood, Department of Zoology, The Natural History Museum, Cromwell Road, London SW7 5BD, UK. E-mail: t.littlewood@nhm.ac. uk Thierry Backeljau, Department of Invertebrates, Royal Belgian Institute of Natural Sciences, Vautierstraat 29, B-1000 Brussels, Belgium. E-mail: thierry.backeljau@naturalsciences.be Ernest R. Schockaert, Research Group Biodiversity, Phylogeny and Population Studies, Centre for Environmental Sciences, Hasselt University, Campus Diepenbeek, Agoralaan Building D, B-3590 Diepenbeek, Belgium. E-mail: ernest.schockaert@uhasselt.be Tom J. Artois, Research Group Biodiversity, Phylogeny and Population Studies, Centre for Environmental Sciences, Hasselt University, Campus Diepenbeek, Agoralaan Building D, B-3590 Diepenbeek, Belgium. E-mail: tom.artois@uhasselt.be Blackwell Publishing Ltd Filling a gap in the phylogeny of flatworms: relationships within the Rhabdocoela (Platyhelminthes), inferred from 18S ribosomal DNA sequences