Animal cells and systems

The Korean Society for Integrative Biology (한국통합생물학회)
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Systematic Relationships of the Urochordates Based on Partial 18S rDNA Sequences

  • Won, Hye-Won (Department of Biological Science, College of Natural Sciences, Ewha Womans University) ;
  • Rho, Boon-Jo (Department of Biological Science, College of Natural Sciences, Ewha Womans University) ;
  • Song, Jun-Im (Department of Biological Science, College of Natural Sciences, Ewha Womans University)
  • Published : 1999.12.01
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Abstract

Urochordates, the most primitive group in phylum Chordata, are mostly sessile as adults although some are free living. Presently, the ancestral stock of urochordates as weir as chordates has been the focus of interest and two conflicting hypotheses have been presented. A free swimming ancestor is one and a sessile, filter feeding ancestor is the other. To clarify the phylogenetic relationships within the urochordates, 22 urochordates and five others as outgroups were used. And we applied neighbor joining, maximum likelihood, and maximum parsimony methods to partial 18S rDNA sequences. The inferred phylogeny in all analyses indicates that order Aplousobranchia of class Ascidiacea appears to be the most ancestral group among urochordates. But it is not clear for the low bootstrap value. The remaining two orders of ascidians, Phlebobranchia and Stolidobranchia, form monophyletic groups respectively, which are well supported by high bootstrap values. These two orders are closer to classes of Thaliacea and Appendicularia than to the Aplousobranchia. While class Appendicularia is strongly supported by the monophyletic group, the phylogenetic position of class Thaliacea is unclear in this study.

Keywords

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