Dm. Odorico et Dj. Miller, INTERNAL AND EXTERNAL RELATIONSHIPS OF THE CNIDARIA - IMPLICATIONS OFPRIMARY AND PREDICTED SECONDARY STRUCTURE OF THE 5'-END OF THE 23S-LIKE RDNA, Proceedings - Royal Society. Biological Sciences, 264(1378), 1997, pp. 77-82
Since both internal (class-level) and external relationships of the Cn
idaria remain unclear on the basis of analyses of 18S and (partial) 16
S rDNA sequence data, we examined the informativeness of the 5'-end of
the 23S-like rDNA. Here we describe analyses of both primary and pred
icted secondary structure data for this region from the ctenophore Bol
inopsis sp., the placozoan Trichoplax adhaerens, the sponge Hymeniacid
on heliophila, and representatives of all four cnidarian classes. Prim
ary sequence analyses clearly resolved the Cnidaria from other lower M
etazoa, supported sister group relationships between the Scyphozoa and
Cubozoa and between the Ctenophora and the Placozoa, and confirmed th
e basal status of the Anthozoa within the Cnidaria. Additionally, in t
he ctenophore, placozoan and sponge, noncanonical base pairing is requ
ired to maintain the secondary structure of the B12 region, whereas am
ongst the Cnidaria this is not the case. Although the phylogenetic sig
nificance of this molecular character is unclear, our analyses do not
support the close relationship between Cnidaria and Placozoa suggested
by previous studies.