TURBEVILLE, J.M.; SMITH, D.M.; Virginia Commonwealth Univ.; Virginia Commonwealth Univ.: Analysis of Nemertean Mitochondrial Gene Arrangements: Implications for Phylogenetic Inference

Nemerteans have played a pivotal role in hypotheses of bilateral metazoan evolution and despite extensive analyses of morphological and gene sequence data separately and simultaneously, the precise placement of the taxon within the Lophotrochozoa remains uncertain. In a recent study, preliminary breakpoint analyses of a subset of metazoan mitochondrial gene orders placed the nemertean Cerebratulus lacteus within an unresolved Lophotrochozoa, a result consistent with unpublished cladistic analyses. To rigorously gauge the utility of gene arrangement characters for reconstructing the phylogenetic position of nemerteans, we are sequencing mitochondrial genomes from a broad sample of nemertean taxa. For heteronemerteans the entire 15 kb genome of C. lacteus and a 5 kb portion of the Myoisophagos sanguineus genome have been sequenced. Protein-coding and tRNA genes determined for these taxa exhibit identical positions, suggesting that arrangements among heteronemerteans are well conserved. The mitochondrial genome of the hoplonemertean Nipponnemertes pulcher has been amplified, cloned and partially sequenced. Arrangements determined for this species suggest that its genome exhibits variation with respect to heteronemertean genomes. Partial data from the genome of the “palaeonemertean” Hubrechtella dubia reveal an arrangement unlike those of the other nemerteans. Our preliminary results indicate that variation in gene order exists within the Nemertea, and thus highlight the importance of broad sampling within a taxon to obtain accurate representation of the phylogenetic signal. Ultimately, arrangement characters should contribute to a more thorough estimation of the placement of nemerteans among the Lophotrochozoa and perhaps to reconstructing relationships within the Nemertea.