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 flatworm Stylochoplana pusilla, distributed in the Japanese Pacific coastal area. Stylochoplana pusilla is known to have commensal relationships with certain intertidal snails, using snails (mainly Monodonta confusa) as a refugee house. During low tide, S. pusilla hides in the mantle cavity of snails to protect themselves from desiccation and predation. Here, we investigated the genetic structure of S. pusilla using a mitochondrial Cytochrome Oxidase I marker and the species diversity of snails used by it. We found that S. pusilla has high genetic diversity of its populations. While S. pusilla showed a significant genetic differentiation among populations, it was relatively low. In addition, we also showed that S. pusilla used several intertidal snail species which inhabit various coastal environments. The present study suggests S. pusilla has sufficient dispersal ability to connect among its local populations. Also, the range of available snails for S. pusilla may help the connectivity among local populations. We provide important knowledge about this invertebrate taxon with a unique ecology, which has been insufficiently studied.

We describe a new genus and a new species of Polycladida, Namyhplana henriettae (Platyhelminthes, Euplanidae), which lives associated with the tubes of the bivalve Bankia martensi in the fjords of the South Pacific Ocean in Chile. This species is characterized by a ribbon-like body, light brown colour, anterior region devoid of pigment, few eyes, no tentacles, pharynx in the anterior region of the body with few folds, independent gonopores anterior to the medial body line, seminal vesicle strongly muscularized, digitiform penian papilla oriented posteroanteriorly, a curled vagina, and a large Lang's vesicle ventral to the intestine. A phylogenetic analysis of the Euplanidae, based on morphological characters, is presented. With the dataset used, the family Euplanidae does not seem to be a monophyletic group. The new species is closely related to Taenioplana teredini (also discussed here) which presents life-habit characteristics that are similar to those of the new species.

Six species of polyclads Pseudobiceros damawan, Pseudobiceros flavocanthus, Pseudoceros bifurcus, Pseudoceros concinnus, Pseudoceros gamblei and Pseudoceros goslineri are newly reported from Andaman and Nicobar Islands of India. Not only do all recorded species constitute first records for the Andaman coast of India, but except for Pseudoceros gamblei, all species are new to Indian waters.