Folks, FYI
Martin, P. 2001. On the origin of the Hirudinea and the demise of the
Oligochaeta. - Proceedings of the Royal Society London, B 268(1471):1089-
1098. [Issue of 22 May 2001.]
Abstract: "The phylogenetic relationships of the Clitellata were
investigated with a data set of published and new complete 18S
rRNA gene sequences of 51 species representing 41 families.
Sequences were aligned on the basis of a secondary structure model
and analysed with maximum parsimony and maximum likelihood. In
contrast to the latter method, parsimony did not recover the
monophyly of Clitellata. However, a close scrutiny of the data
suggested a spurious attraction between some polychaetes and
clitellates. As a rule, molecular trees are closely aligned with
morphology-based phylogenies. Acanthobdellida and Euhirudinea
were reconciled in their traditional Hirudinea clade and were
included in the Oligochaeta with the Branchiobdellida via the
Lumbriculidae as a possible link between the two assemblages.
While the 18S gene yielded a meaningful historical signal for
determining relationships within clitellates, the exact position of
Hirudinea and Branchiobdellida within oligochaetes remained
unresolved. The lack of phylogenetic signal is interpreted as
evidence for a rapid radiation of these taxa. The placement of
Clitellata within the Polychaeta remained unresolved. The
biological reality of polytomies within annelids is suggested and
supports the hypothesis of an extremely ancient radiation of
polychaetes and emergence of clitellates."
--
Geoff Read <g.read at niwa.cri.nz>
http://www.annelida.net/
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