title: Genus Tetrastemma Ehrenberg, 1831 (Phylum Nemertea)--a natural group? Phylogenetic relationships inferred from partial 18S rRNA sequences.
abstract: We investigated the monophyletic status of the hoplonemertean taxon Tetrastemma by reconstructing the phylogeny for 22 specimens assigned to this genus, together with another 25 specimens from closely related hoplonemertean genera. The phylogeny was based on partial 18S rRNA sequences using Bayesian and maximum likelihood analyses. The included Tetrastemma-species formed a well-supported clade, although the within-taxon relationships were unsettled. We conclude that the name Tetrastemma refers to a monophyletic taxon, but that it cannot be defined by morphological synapomorphies, and our results do not imply that all the over 100 species assigned to this genus belong to it. The results furthermore indicate that the genera Amphiporus and Emplectonema are non-monophyletic.
authors.affiliation: Göteborg University, Department of Zoology, Gothenborg, Sweden.
authors.forename: Malin
authors.initials: M
authors.lastname: Strand
authors.forename: Per
authors.initials: P
authors.lastname: Sundberg
mesh_terms: D000818:Animals; D001483:Base Sequence; D001499:Bayes Theorem; D002965:Classification / Q000379:methods; D019143:Evolution, Molecular; D007448:Invertebrates / Q000145:classification* / Q000235:genetics*; D016013:Likelihood Functions; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D012335:RNA, Ribosomal; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017423:Sequence Analysis, RNA
chemical_list: D012335:RNA, Ribosomal