长腹剑水蚤属是广泛分布于海洋近岸和外海海域的中小型桡足类中最为丰富的类群之一，既是食屑者，又是主要的中间捕食者，在生物地理遗传学与海洋生态学研究中均具有重要地位。长腹剑水蚤属个体小且形态差异微小，通过传统的形态学分类法对其进行准确鉴定难度较大。而长腹剑水蚤属种间存在较大的区域遗传分化，应用分子标记研究长腹剑水蚤属遗传关系，为上述问题的解决提供了新的方法与途径。本研究以其遗传进化与地理分布的关系为切入点，通过PCR和DNA测序方法获取中国海域不同区域的长腹剑水蚤属COI基因与28S rDNA序列，并将两序列信息联合建立系统进化树，分析长腹剑水蚤属的遗传进化关系，探讨遗传与地理分布之间的关系，发现长腹剑水蚤属中存在的隐种，丰富我国海洋生物多样性库，以期为浮游生物分子进化和地理遗传学、海洋食物网结构与功能、气候变化对海洋生态系统影响的深入和系统研究提供基础资料和有益借鉴。

The genus Oithona ,including intermediate- to smaller-sized (<1mm) cyclopoid copepods, is widely distributed and occurs in all kinds of marine environments (estuarine, coastal and oceanic waters). The role of the genus Oithona was recently recognized in terms of their numerical contribution to the meso- zooplankton and particularly their high turnover rates was proved to have a pivotal position in food webs, microbial loops, and in carbon cycling. Therefore, the genus Oithona has the important position in geographic genetics and marine ecological research. However, routine identification of the species has remained challenging due to the small body size and subtle mophological differences among them. It has also been observed that intraspecific genentic variations exist in Oithona sp.. Analysis of the genetic relationship in the genus Oithona with molecular marker would reveal a new perspective to overcome those scientific questions. To find geographic genetic variations of the genus Oithona, a phylo- genetic tree is reconstructed based on the sequences of COI and 28S genes of the genus from Chinese sea through PCR and DNA mapping. After that, genetic evolution of the genus is analyzed with the phylogenetic tree to isolate cryptic species enriching the marine biological library and make the relationship between genetic evolution and geographical ranges of the genus clear that is intended to provide useful reference for study on planktonic molecular genetics and geographic genetics, the structure and function of marine food web, andthe impact of climate changes on marine ecology.