Molecular phylogeny

Geoff Read at
Wed Jan 3 22:41:23 EST 2001

Greetings & a happy new millennium to all Annelida members,  

Phizzzzz, whooosh, kapowweee! There you go - imagine if you can some 
virtual fireworks making sinuous wormy shapes in the sky in celebration of 
the occasion.  :^)  

Now back to earth (& sea) with the progress of worm research.   Damhnait 
McHugh's latest paper is  a  nice wide-ranging review of the state of play 
with the annelid molecules. Here's the cite and abstract.  

McHugh, D. 2000. Molecular phylogeny of the Annelida. - Canadian 
Journal of Zoology   Revue Canadienne de Zoologie 78(11):1873-1884.  

"Traditionally, the Annelida has been classified as a group comprising the 
Polychaeta and the Clitellata. Recent phylogenetic analyses have led to 
profound changes in the view that the Annelida, as traditionally formulated, 
is a natural, monophyletic group. Both molecular and morphological 
analyses support placement of the Siboglinidae (formerly the 
Pogonophora) as a derived group within the Annelida; there is also 
evidence, based on molecular analysis of the nuclear gene elongation 
factor-1 alpha, that the unsegmented echiurids are derived annelids. While 
monophyly of the Clitellata is well-supported by both molecular and 
morphological analyses, there is no molecular evidence to support 
monophyly of the polychaete annelids; the Clitellata fall within a 
paraphyletic polychaete grade. Relationships among groups of polychaete 
annelids have not yet been resolved by molecular analysis. Within the 
Clitellata, paraphyly of the Oligochaeta was indicated in a phylogenetic 
analysis of cytochrome c oxidase I, which supported a sister relationship 
between the leeches, including an acanthobdellid and a branchiobdellid, 
and two of the four oligochaetes in the analysis. There is some evidence 
from analysis of 18S rRNA sequences for a sister-group relationship 
between the clitellates and the taxon Aeolosoma. There is no agreement 
regarding the body form of the basal annelid, and while molecular analyses 
provide strong support for the Eutrochozoa, the identity of sister-group to 
the Annelida among the Eutrochozoa remains enigmatic. It is 
recommended that future investigations include additional conserved gene 
sequences and expanded taxon sampling. It is likely that the most 
productive approach to resolving annelid phylogeny, and thus increasing 
our understanding of annelid evolution, will come from combined analyses 
of several gene sequences.   

  Geoff Read < at>

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