Phylogenetic Relationships Of The Main Bryozoan Lineages Based On LSU(28S) RDNA Sequences

The partial LSU rDNA (28S rDNA) sequences of eighteen species of bryozoans and the complete 28S rDNA sequences of three representative species of bryozoan lineages were amplified and sequenced. Diploblastic cnidarians as the outgroups, the phylogenetic trees of bryozoans and lophotrochozoans were reconstructed by the 28S rDNA analyses of theirs and other related bilaterians obtained through GenBank with different methods, respectively. Meanwhile, the primary and predicted secondary structures of their partial divergent 28S rDNA domains were compared and analysed.The 28S rDNA molecular phylogenetic trees showed: 1) entoprocts and phylactolaemate ectoprocts constituted a sister group, strenghthening the opinion that entoprocts should be reunited into phylum Bryozoa; 2) the cheilostome gymnolaemates was obviously non-monophyletic; 3) bryozoans itself was polyphyletic beyond any doubt, its main lineages were scattered in different positions of the lophotrochozoan trees; 4) to our great interests, the phylogenetic position of cheilostomes was between the diploblastic and the triploblastic, indicating they may play an important role during the evolution route from the diplobastic to the triploblastic animals. Additionally, our results showed that the phylogenetic relationships based on the morphological characteristics of their secondary structures are consistent with those inferred from the primary structures and other features, and this fact suggests that the molecular morphology is also the valuable source for the phylogenetic consideration.