Based on specimens from the gill cavities of one Platichthys stellatus individual collected in the Sea of Japan, we investigated the taxonomic status of the enigmatic caligid genus Pseudolepeophtheirus and its type species, Pseudolepeophtheirus longicauda. In a maximum likelihood (ML) tree based on 18S rRNA gene sequences, the sequence from our sample was nested in a well-supported Lepeophtheirus clade, along with the type species, confirming that Pseudolepeophtheirus should be considered a junior synonym of Lepeophtheirus; our morphological data support this synonymy. Although a previous study had synonymized Pseudolepeophtheirus longicauda with Lepeophtheirus parvicruris, we found that the former differs morphologically from the latter in having a short leg-4 exopod, with the articulation between the first and second segments not evident (the shape of the posterior striated membrane on the leg-2 intercoxal sclerite also differs between two species), and detected slight differences in 18S rRNA sequences between two taxa. We thus concluded that this synonymy is invalid, and reinstate Lepeophtheirus longicauda as a valid species. A ML analysis of COI sequences from Pl. stellatus (the host fish for both L. longicauda and L. parvicruris) showed the host species to comprise distinct northwestern- and northeastern-Pacific clades. Lepeophtheirus longicauda is distributed in the northwestern Pacific and L. parvicruris in the northeastern Pacific, indicating co-divergence of the two copepod species with the host lineages.

基于在日本海中采集的一只Plateththythys stellatus ill腔的标本，我们研究了神秘的ig属Pseudolepeophtheirus及其类型物种Pseudolepeophtheirus longicauda的分类状况。在基于18S rRNA基因序列的最大似然（ML）树中，来自我们样本的序列与类型物种一起嵌套在良好支持的Lepeophtheirus进化枝中，证实了Pseudolepeophtheirus应该被视为Lepeophtheirus的初级同义词；我们的形态学数据支持这一同义词。尽管先前的研究已将Pseudolepeophtheirus longicauda与Lepeophtheirus parvicruris，我们发现前者在形态上与后者不同，在于腿4外突短，第一节和第二节之间的关节连接不明显（腿2内巩膜后巩膜的形状也不同） （两个物种之间），并且检测到两个分类群之间18S rRNA序列略有差异。因此，我们得出的结论是，该同义词无效，并且将Lepeophtheirus longicauda恢复为有效物种。来自P1的COI序列的ML分析。鲽（主机鱼两个大号。长尾和大号。parvicruris）显示宿主物种由西北太平洋和东北太平洋进化枝组成。Lepeophtheirus长尾分布在西北太平洋和大号。东北太平洋的parvicruris，表明这两种co足类物种与宿主谱系共同散布。