Molecular Phylogeny of the Polychaeta
The Polychaeta are a major invertebrate group principally consisting of marine worms that are closely related to earthworms and leeches. It is a very diverse group, consisting of 90 or more families of which their relative relationships are little understood.
Phylogenetically, the Polychaeta have been the least understood of the major invertebrate clades. Polychaetes are currently classified into more than 90 families and lack a satisfactory phylogenetic hypothesis. The group lacked a higher level classification, with its position being uncertain with respect to the Oligochaeta, and the two doubtful phyla Vestimentifera and Echiura. In 1997, Rouse and Fauchald (Zool. Scripta 26 : 139-204) published the first cladistically-based classification using a morphological character set from eighty polychaete families. Some of the main clades within the group were well supported, but the majority of basal nodes had very few synapomorphies.
To further investigate the phylogeny of the polychaete group, we surveyed 3 genes; Histone H3, U2 snRNA and two segments (D1 and D9-10) of 28S rDNA, from 34 species, including outgroups Echiura, Clitellata, and Sipuncula.
Results of maximum parsimony analyses for each of the gene sets were inconsistent. Each data set provided corroboration to only a few of the morphological groupings, pairing familial members, and generally did not conform to the previous results of those based on morphological data. Higher groupings were rarely resolved.
Maximum parsimony analysis of the combined data recovered the following morphological groupings: Cirratulidae, Terebellidae, scale worms and eunicimorphs and did not seriously contradict others. Some expected groups based were not recovered: the fanworms (Sabellidae and Serpulidae) were not shown as sister taxa, and monophyly of the Phyllodocida despite being well corroborated morphologically. The morphologically defined higher group Aciculata, proposed by Rouse and Fauchald (1977), was not seen in the analysis. However if the trees recovered in our analysis were rooted on sipunculians rather than the nematode, Aciculata is nearly recovered. The morphologically aberrant Sternapsidae are closest to members of Terebellida in the analysis, supporting Rouse and Fauchald's (1997) placement. Results of interest deserving further assessment concern the placement of Chaetopteridae, Oweniidae and Sipunculia.
Participants
Sarah Brown
Greg Rouse, School of Biological Sciences, The University of Sydney.
Pat Hutchings
Dr Don Colgan
Copyright © 2003, Australian Museum
