Phylogenetic confirmation of the genus Robbea (Nematoda: Desmodoridae, Stilbonematinae) with the description of three new species.

The Stilbonematinae are a monophyletic group of marine nematodes that are characterized by a coat of thiotrophic bacterial symbionts. Among the ten known genera of the Stilbonematinae, the genusRobbeaGerlach1956 had a problematic taxonomic history of synonymizations and indications of polyphyletic origin. Here we describe three new species of the genus,R. hypermnestrasp. nov.,R. ruetzlerisp. nov. andR. agricolasp. nov., using conventional light microscopy, interference contrast microscopy and SEM. We provide 18S rRNA gene sequences of all three species, together with new sequences for the generaCatanemaandLeptonemella. Both our morphological analyses as well as our phylogenetic reconstructions corroborate the genusRobbea. In our phylogenetic analysis the three species of the genusRobbeaform a distinct clade in the Stilbonematinae radiation and are clearly separated from the clade of the genusCatanema, which has previously been synonymized withRobbea. Surprisingly, inR. hypermnestrasp. nov. all females are intersexes exhibiting male sexual characters. Our extended dataset of Stilbonematinae 18S rRNA genes for the first time allows the identification of the different genera, e.g. in a barcoding approach. http://zoobank.org/urn:lsid:zoobank.org:pub:D37C3F5A-CF2B-40E6-8B09-3C72EEED60B0 [ABSTRACT FROM PUBLISHER]