The phylogenetic relationships of orbiniid taxa were reconstructed based on sequence data of the mitochondrial 16S rRNA and nuclear 18S rRNA genes. Both genes were analysed separately and in combination using maximum likelihood, Bayesian inference and maximum parsimony. Regardless of the method used, a clade consisting of the investigated Orbiniidae,
Methanoaricia dendrobranchiata and
Questa was strongly supported by the 18S dataset. The analysis of the combined dataset suggests inclusion of
M. dendrobranchiata within the Orbiniidae with close relationships to species of
Orbinia and
Phylo, rather than as a sister taxon to all other orbiniids. Evidence is given for the paraphyletic status of
Leitoscoloplos,
Naineris,
Orbinia,
Phylo and
Scoloplos, which represent the most species-rich genera of the Orbiniidae. It is thus reasoned that the morphological characters presently used for genus diagnosis are not informative for cladistic analysis. No support is found for the hypothesis that taxa of the Protoariciinae represent juveniles of Orbiniinae. Instead, in the case of
Protoaricia oerstedi, strong support for a progenetic origin is found.
