title: A molecular phylogenetic framework for the phylum Ctenophora using 18S rRNA genes.
abstract: This paper presents the first molecular phylogenetic analysis of the phylum Ctenophora, by use of 18S ribosomal RNA sequences from most of the major taxa. The ctenophores form a distinct monophyletic group that, based on this gene phylogeny, is most closely related to the cnidarians. Our results suggest that the ancestral ctenophore was tentaculate and cydippid-like and that the presently recognized order Cydippida forms a polyphyletic group. The other ctenophore orders that we studied (Lobata, Beroida, and Platyctenida) are secondarily derived from cydippid-like ancestors, a conclusion that is also supported by developmental and morphological data. The very short evolutionary distances between characterized ctenophore 18S rRNA gene sequences suggests that extant ctenophores are derived from a recent common ancestor. This has important consequences for future studies and for an understanding of the evolution of the metazoans.
authors.affiliation: Department of Molecular Diversity, Diversa Corp., 4955 Directors Place, San Diego, California 92121, USA.
authors.forename: M
authors.initials: M
authors.lastname: Podar
authors.forename: S H
authors.initials: SH
authors.lastname: Haddock
authors.forename: M L
authors.initials: ML
authors.lastname: Sogin
authors.forename: G R
authors.initials: GR
authors.lastname: Harbison
mesh_terms: D000818:Animals; D004247:DNA / Q000737:chemistry / Q000235:genetics; D021903:DNA, Ribosomal Spacer / Q000235:genetics; D019143:Evolution, Molecular; D007448:Invertebrates / Q000145:classification / Q000235:genetics*; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D010802:Phylogeny; D012337:RNA, Ribosomal, 18S / Q000737:chemistry / Q000235:genetics*; D012340:RNA, Ribosomal, 5.8S / Q000235:genetics; D017422:Sequence Analysis, DNA
chemical_list: D021903:DNA, Ribosomal Spacer; D012337:RNA, Ribosomal, 18S; D012340:RNA, Ribosomal, 5.8S; D004247:DNA