Redescription of wood-associated tanaidacean Protanais birsteini (Kudinova-Pasternak, 1970) and its relationship within the Tanaididae

During the KuramBio Expedition on board the R/V Sonne in 2012 a sunken piece of wood debris was collected from a depth of over 5000 m. Among the recovered fauna twelve specimens of tanaidacean peracarid were identified as Protanais birsteini Kudinova-Pasternak. It is only the second finding of the species and the fourth record of the genus Protanais, whose distribution is restricted so far to the North Pacific. In this paper we redescribe the species and report on its stomach contents, which contain wood tissue crumbled in different degrees in posterior parts of the digestive system. This observation suggests that these tanaids might be xylophagous. In addition we report the presence of cells of unidentified protists attached to the mouthparts of P. birsteini, and filaments of bacteria, which densely covered the appendages of the largest specimens. Bayesian and maximum likelihood molecular analyses confirm the placement of P. birsteini within Tanaididae, and highlight some taxonomic questions requiring further research.