Progenesis in Eunicida ("Polychaeta," Annelida)--separate evolutionary events? Evidence from molecular data.

The Eunicida are a well-defined annelid taxon currently comprising Dorvilleidae, Lumbrineridae, Eunicidae, Onuphidae, and Hartmanniellidae. Especially the Dorvilleidae include several species of small body size and apparently simple organisation, resembling larvae and juveniles of larger species. One hypothesis to explain the evolution of such species is progenesis. By this criterion the Dinophilidae were included in this group as well. Although their overall similarity suggests monophyly, parallel evolution of such progenetic taxa cannot be excluded. To infer the phylogeny of Eunicida and their presumed relationship to Dinophilidae and progenetic dorvilleids, 18S rDNA sequences from various Dinophilidae, Dorvilleidae, and members of other Eunicida were determined. The data matrix were extended by adding sequences from several annelid and molluscan species and analysed with maximum-parsimony, distance, and maximum-likelihood algorithms. Highly significant bootstrap-values support monophyly of the Dinophilidae, of a clade enclosing the Eunicidae and the Onuphidae, and of a dorvilleid group comprising six species including the presumed progenetic Parapodrilus psammophilus. The position of the Dinophilidae remains unresolved, so that their inclusion within the Eunicida can neither be corroborated nor rejected. However, a constraint monophyly of Dinophilidae and P. psammophilus is rejected by several tests, substantiating the hypothesis of separate progenetic evolutionary events. Furthermore, the molecular data indicate polyphyly of the Dorvilleidae.