Origins of holopelagic Typhloscolecidae and Lopadorhynchidae within Phyllodocidae (Phyllodocida, Annelida)

Abstract

Several distinct lineages of annelids have evolved holopelagic life styles. Unfortunately, our knowledge of the biology and evolution of most of these groups is limited. Typhloscolecidae and Lopadorhynchidae are two such examples of recognized families of holopelagic annelids about which little is known. Both groups have a limited number of known species (13 and 15, respectively) and are rarely discussed in the literature other than to note occurrence. Placing these groups in a phylogenetic context has been difficult due to their seemingly unique morphology, and, to the best of our knowledge, lack of molecular data. Nonetheless, previous authors have suspected that they are members of Phyllodocida and perhaps within Phyllodocidae. To test such hypotheses, we have employed nuclear 18S and 28S ribosomal data in both a Bayesian inference and a maximum-likelihood framework. The resultant topology indicates that typhloscolecids and lopadorhynchs are sister taxa nested within Phyllodocidae near another holopelagic taxon, alciopids. Whereas posterior probabilities strongly support this placement, an AU hypothesis testing approach and bootstrap values are more equivocal but both still strongly suggest Phyllodocidae affiliations. Recognition of Typhloscolecidae and Lopadorhynchidae as annelid families is called into question.