中文摘要：

采用18SrRNA对我国常见的4种三肠目涡虫的18SrDNA基因进行序列测定和分析，共获得三肠目2科3属4种的序列，同时结合GenBank中的三肠目18SrDNA序列（22条），以其姐妹群原序列目中的Archimonoceliscrw／fer为外群，采用MEGA3．0、PHYLIP、PAUP4．0等分子生物学软件分别构建NJ树、ME树、MP树和ML树，分析三肠目的系统发育关系。结果表明，不同构树方法所得系统树的拓扑结构基本一致。

英文摘要：

In order to investigate system development relationship Turbellarian tricladida in the molecular level, fragments of 18S rDNA, as gene marker, were sequenced for 4 species from 3 genera of the Paludicola, and the homologous sequences of Tricladida downloaded fi＇om GenBank. After alignment for these sequences of 22 species of Tricladida with choosing Archimonocelis crucifer as outgroup, the phylogenetic relationships among 22 species of three suborders of Tricladida were studied. Meanwhile, four phylogenetic trees, such as NJ tree, ME tree, ML tree and MP tree, were reconstructed with some molecular biology software that was MEGA 3.0, PHYLIP and PAUP 4.0. Subsequently, the topologv of four phvlogenetic trees were found to be consensus on the whole.