A molecular phylogenetic framework for the phylum Ctenophora using 18S rRNA genes. |
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Authors: | M Podar S H Haddock M L Sogin G R Harbison |
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Affiliation: | Department of Molecular Diversity, Diversa Corp., 4955 Directors Place, San Diego, California 92121, USA. |
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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. |
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