Phylogenetic analysis of the mitochondrial cytochrome c oxidase subunit 1 gene from 13 sipunculan genera: intra- and interphylum relationships

摘要

Sipunculans are a phylum of non-segmented, marine worms. Although they are well characterized morphologically, relationships within the phylum and the relationship of Sipuncula to other spiralian phyla have been strongly debated. I analyzed representatives of 13 of 17 described genera using a 654-bp fragment of the mitochondrial gene, cytochrome c oxidase subunit 1, to construct the first intraphylum phylogenetic hypothesis for sipunculans based on molecular sequence data. Within the phylum, tree topologies are loosely congruent with a previously published morphological analysis, except that the monotypic genus Phascolopsis occurred within the Golfingiaformes as a sister group to, or nested within, the Themistidae. Phylogenetic analyses, including 30 sequences from additional invertebrate taxa, suggest that sipunculans are most closely related to the Annelida (including Echiura). A previously proposed sipunculan-molluscan relationship is not supported. While not universally accepted, this hypothesis is consistent with other recent and past data on phylum-level relationships. [References: 56]