. 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.

A morphological and taxonomic account of the genus Trigonostomum is provided. All known species are discussed and briefly re‐described where necessary. Seven new species are described: T. franki from Curaçao, Florida (USA), the East African Coast and New Caledonia, T. nataschae from the French sub‐Antarctic island Kerguelen, T. spinigerum from New Caledonia and T. watsoni from the Australian East Coast and New Caledonia. T. tori and T. galapagoensis, both formerly enclosed in T. setigerum, are considered new species, while T. australis also belongs to the same species group. Proxenetes denhartogi is transferred to Trigonostomum. Based on a comparison of old and new material, T. marki is synonymized with T. penicillatum, while T. prytherchi and T. divae are regarded as junior synonyms of T. lilliei; T. intermedium and T. quadrifolium are considered synonyms of T. coronatum. Three species are considered species inquirendae: T. brunchorsti, T. piriforme and Marinellia lingulifera. Similarities and differences of the 17 valid species are discussed and summarized in an identification key. © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society, 2004, 141, 271–296.

This contribution reviews diversity of turbellarian species by biogeographical regions, with comments on species biology. The review draws on the database available at http://www.devbio.umesci. maine.edu/styler/turbellaria. Comparisons between regions suggest that species richness may be at least one order of magnitude higher than the currently reported number of species. In the context of the recent reconstructions of phylogeny of Platyhelminthes based on molecular data, the paper allows inferences as to the history of colonization of freshwaters by turbellarians. Specifically, four, or perhaps six, major invasions of freshwater habitats may have occurred in the Pangean period, each of which gave rise to a monophyletic freshwater taxon. In addition, several occasional invasions by representatives of marine taxa must have taken place.

No abstract

Recent data and opinions on meiofaunal ecology are briefly reviewed ; and from scattered data, the place of turbellarians in the meiobenthic community is discussed . Turbellarian diversity, density, and biomass are higher in sandy habitats than in muddy bottoms . In sand, turbellarian diversity is of the same magnitude as that of other important meiofaunal taxa, while densities range between 7-25% of the total meiofauna . Mean individual turbellarian dry weight seems to be four times that of nematodes and in sandy habitats turbellarian biomass may be equal to or excede that of nematodes. Most turbellarian species may be considered as predators and in this respect may take the place occupied by macrofaunal species in muddy sediments . mens .