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Vol. 47 No. 3, 2008
Multi-Gene Analyses of the Phylogenetic Relationships among the Mollusca, Annelida, and Arthropoda
Donald J. Colgan1,*, Patricia A. Hutchings2, and Emma Beacham1
1Evolutionary Biology Unit, The Australian Museum, 6 College St. Sydney, NSW 2010, Australia
2Marine Invertebrates, The Australian Museum, 6 College St., Sydney, NSW 2010, Australia
Donald J. Colgan, Patricia A. Hutchings, and Emma Beacham (2008)
The current understanding of metazoan relationships is largely based on
analyses of 18S ribosomal RNA ('18S rRNA'). In this paper, DNA
sequence data from 2 segments of 28S rRNA, cytochrome c
oxidase subunit I, histone H3, and U2 small nuclear (sn)RNA were
compiled and used to test phylogenetic relationships among the
Mollusca, Annelida, and Arthropoda. The 18S rRNA data were
included in the compilations for comparison. The analyses were
especially directed at testing the implication of the Eutrochozoan
hypothesis that the Annelida and Mollusca are more closely related than
are the Annelida and Arthropoda and at determining whether, in contrast
to analyses using only 18S rRNA, the addition of data from other genes
would reveal these phyla to be monophyletic. New data and
available sequences were compiled for up to 49 molluscs, 33 annelids,
22 arthropods, and 27 taxa from 15 other metazoan phyla. The
Porifera, Ctenophora, and Cnidaria were used as the outgroup. The
Annelida, Mollusca, Entoprocta, Phoronida, Nemertea, Brachiopoda, and
Sipuncula (i.e., all studied Lophotrochozoa except for the Bryozoa)
formed a monophyletic clade with maximum likelihood bootstrap support
of 81% and a Bayesian posterior probability of 0.66 when all data were
analyzed. The clade was also formed (including 1 arthropod, a
symphylan) when only genes other than 18S rRNA were analyzed. Two
molluscan genera with long branch lengths (Nautilus and Philippia)
were removed from the Lophotrochozoa in the maximum-parsimony analyses
of all data. The Ecdysozoa (comprised of the Kinorhyncha,
Priapula, Nematoda, Onychophora, Tardigrada, and Arthropoda) was
included in a clade with the Chaetognatha (with maximum-likelihood
support of 80% and a Bayesian probability of 0.57) using the total
data. This clade except the symphylan had a Bayesian probability
of 0.66 when 18S r DNA data were excluded. The reciprocal
separation of the Annelida and Mollusca was generally supported where
this could be resolved. The monophyly of the Annelida was
contradicted only by the inclusion of the Sipuncula and Brachiopoda and
the exclusion of Owenia. Molluscan monophyly was contradicted by
the anomalous placement of Nautilus and/or Philippia, but these taxa were never placed in the Annelida.
Key words: Phylogenetics, Lophotrochozoa, Eutrochozoa, Ecdysozoa, Basal Annelida.
*Correspondence: E-mail:don.colgan@austmus.gov.au
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