苔藓动物18S rRNA基因的分子系统发生初探

本文对我国沿海较为常见的8种唇口目苔藓动物的18SrRNA基因进行了PCR扩增和序列测定。结合已知的其它苔藓动物（包括内肛动物和外肛动物）以及腕足动物和帚虫的相应序列，运用分子系统学方法，研究苔藓动物门的系统发生关系，结果表明，外肛动物和内肛动物构成苔藓动物分子系统树中的二大平行支；本文测定的大室膜孔苔虫与Giribet等测定的膜孔苔虫在系统树中的位置间隔较远。结果也支持外肛动物包含被唇纲和裸唇纲两大类群的形态划分，而关于裸唇纲特别是唇口目内部的系统发生关系。分子数据的分析结果和形态分类之间的分歧有待于进一步研究。

PRELIMINARY STUDY ON MOLECULAR PHYLOGENY OF BRYOZOANSBASED ON 18S rRNA GENE SEQUENCES

The 18S rRNA gene of eight species of cheilostome bryozoans commonly found in the coastal waters of China were amplified through the polymerase chain reaction(PCR) and the sequences from the PCR products were determined directly. Combined with the sequences of other bryozoans including entoprocts, ectoprocts, brachiopods and phoronids, we reconstructed the molecular phylogenetic trees using the molecular evolutionary genetics analysis(MEGA, version 2.0) software with the neighbour joining(NJ) and maximum parsimony(MP) methods. The results show that the entoprocts and the ectoprocts constitute the two parallel branches in the molecular phylogenetic trees of bryozoans; the position of Membranipora grandicella studied in this paper and that of Membranipora sp. as reported by Giribet et al. (2000) is rather far away from each other in the trees. The results also support the two class morphological classification of Phylactolaemata and Gymnolaemata of ectoprocts. As for the phylogenetic relationships among the main groups of Gymnolaemata, especially Cheilostomida, the discrepancy between the molecular data and the morphological characters awaits further studies.