Although Cyclops vicinus Uljanin, 1875 and C. kikuchii Smirnov, 1932 are broadly distributed in Eurasia, the genetic divergences between European and Asian populations have been investigated in neither species. In Japan, the nomenclature and distinction between these two congeners are still questionable (thus, hereafter C. vicinus s.l.). We determined the taxonomic position of the Japanese C. vicinus s.l. by morphological analyses and by sequencing nuclear internal transcribed spacer 1(ITS-1) and the mitochondrial 12S (mt12S) genes. The ITS-1 phylogeny separated Japanese C. vicinus s.l. into two genetic groups; one was clustered with European C. kikuchii (thus, CkikJPN), while the other was clustered with European C. vicinus (thus, CvicJPN). Morphological analyses using the lengths of terminal furcal setae revealed that CkikJPN and CvicJPN correspond to C. kikuchii and C. vicinus, respectively. These results revealed that C. vicinus and C. kikuchii in Japan are confidently the same species as those in Europe. The degree of divergence in the mt12S between Japanese and European populations varied largely between the species, as it was nearly at the interspecific level in C. kikuchii, while it was at the intraspecific level in C. vicinus; it is the first case in which the genetic divergence between the European and Asian population is greatly different among closely related species of freshwater copepods.

尽管1875年的独眼巨人Uljanin和1932年的菊苣斯米尔诺夫（C. kikuchii Smirnov）广泛分布于欧亚大陆，但尚未对欧洲和亚洲种群之间的遗传差异进行调查。在日本，这两个同类物的命名和区别仍然令人怀疑（因此，下文称为C. vicinus sl）。我们通过形态分析和对核内转录间隔子1（ITS-1）和线粒体12S（mt12S）基因进行测序，确定了日本C. vicinus sl的分类位置。ITS-1的系统发育将日本锦鲤C. ssl分为两个遗传组。一个与欧洲菊苣（因此，CkikJPN），而另一个则与欧洲C. vicinus（因此，CvicJPN）聚集在一起。形态学分析使用终端furcal刚毛的长度显示，CkikJPN和CvicJPN对应于C.松毛虫和C. vicinus分别。这些结果表明，日本的C. vicinus和菊苣C.无疑是与欧洲的相同物种。在日本和欧洲种群之间，mt12S的差异程度在物种之间差异很大，因为它在菊苣角藻中几乎处于种间水平，而在角藻中处于种内水平。; 这是首次在密切相关的淡水co足类物种之间，欧洲和亚洲人口之间的遗传差异大为不同的情况。