S. Brown et al., Assessing the usefulness of histone H3, U2 snRNA and 28S rDNA in analyses of polychaete relationships, AUST J ZOOL, 47(5), 1999, pp. 499-516
DNA sequence data from for histone H3 (34 species), U2 snRNA (34 species) a
nd two segments (D1 and D9-10 expansion regions) of 28S rDNA (28 and 26 spe
cies, respectively) have been collected to investigate the relationships of
polychaetes. Representatives of all of the major morphologically identifie
d clades were used, as well as members of the Sipuncula, Echiura, Turbellar
ia, Clitellata and Siboglinidae (formerly the phyla Pogonophora and Vestime
ntifera).
Maximum parsimony analyses of the separate data sets gave conflicting resul
ts and none conformed closely to previous results based on morphology. Inst
ead each data set provided corroboration of a few of the morphological grou
pings, usually pairing, though inconsistently, members of the same family.
Higher groupings proposed on morphological grounds were rarely recovered.
Maximum parsimony analysis of the combined data, excluding areas of uncerta
in alignment, recovered some morphological groupings such as Cirratulidae,
Terebellidae, scale worms and eunicimorphs, and did not significantly contr
adict others. However, some expected groupings were not recovered. Surprisi
ngly, the fanworms (Sabellidae and Serpulidae) were not shown as sister tax
a, and monophyly of Phyllodocida, a morphologically well corroborated clade
, required four more steps than most parsimonious trees. Aciculata was not
seen in our analyses, although it was the most strongly supported large cla
de in Rouse and Fauchald (1997, Cladistics and polychaetes. Zoologica Scrip
ta 26, 138-204). Trees constrained to show Aciculata as monophyletic were 1
8 steps longer than the most parsimonious trees. If trees are rooted on sip
unculans rather than the nematode, Aciculata is nearly recovered, being ren
dered paraphyletic by the inclusion of the sister-pair of Oweniidae and Cha
etopteridae.
As suggested by some recent morphological and molecular analyses, Siboglini
dae and Clitellata may well have sister groups among polychaetes. The morph
ologically aberrant Sternaspidae are closest to members of Terebellida in t
he present analyses, supporting the placement of Rouse and Fauchald. Intere
sting results deserving further assessment concern the placement of Chaetop
teridae, Oweniidae and Sipuncula.