Although marine phylogeographers have accumulated knowledge of the evolutionary history of various invertebrates, there is a large bias among the taxa regarding genetic data. The order Polycladida is a typical example for which little genetic information at population level is available. Here, we focused on the polyclad flatwormStylochoplana pusilla, distributed in the Japanese Pacific coastal area.Stylochoplana pusillais known to have commensal relationships with certain intertidal snails, using snails (mainlyMonodonta confusa) as a refugee house. During low tide,S. pusillahides in the mantle cavity of snails to protect themselves from desiccation and predation. Here, we investigated the genetic structure ofS. pusillausing a mitochondrial Cytochrome Oxidase I marker and the species diversity of snails used by it. We found thatS. pusillahas high genetic diversity of its populations. WhileS. pusillashowed a significant genetic differentiation among populations, it was relatively low. In addition, we also showed thatS. pusillaused several intertidal snail species which inhabit various coastal environments. The present study suggestsS. pusillahas sufficient dispersal ability to connect among its local populations. Also, the range of available snails forS. pusillamay help the connectivity among local populations. We provide important knowledge about this invertebrate taxon with a unique ecology, which has been insufficiently studied.

中文翻译：

---

海洋扁虫Stylochoplana pusilla（Rhabditophora: Polycladida）的遗传结构及其对潮间带蜗牛的利用

尽管海洋系统地理学家已经积累了各种无脊椎动物进化史的知识，但在遗传数据方面，分类群之间存在很大偏差。Polycladida 目是一个典型的例子，其种群水平的遗传信息很少。在这里，我们专注于多囊扁虫小柱藻，分布于日本太平洋沿岸地区。小柱藻已知与某些潮间带蜗牛有共生关系，使用蜗牛（主要是斑齿鱼) 作为难民之家。退潮时，S. pusilla隐藏在蜗牛的地幔腔中以保护自己免受干燥和捕食。在这里，我们研究了它的遗传结构S. pusilla使用线粒体细胞色素氧化酶 I 标记和它使用的蜗牛的物种多样性。我们发现S. pusilla其种群的遗传多样性很高。尽管S. pusilla种群间遗传分化显着，相对较低。此外，我们还证明了S. pusilla使用了几种栖息在各种沿海环境中的潮间带蜗牛物种。本研究表明S. pusilla有足够的传播能力在当地人口之间建立联系。此外，可用蜗牛的范围S. pusilla可能有助于当地人口之间的联系。我们提供了关于这种具有独特生态学的无脊椎动物分类群的重要知识，这些知识尚未得到充分研究。