Two new species of Schizorhynchia (Kalyptorhynchia, Rhabdocoela, Platyhelminthes) from Japan

Abstract

Schizorhynchia is a group of free-living interstitial flatworms within Kalyptorhynchia, characterized by possessing a split proboscis. To date, only seven species of Schizorhynchia have been recorded from Japan. Here, we describe two new species of schizorhynchs, Proschizorhynchella quadricaudata sp. nov. and Cheliplana izuensis sp. nov., based on specimens collected from the intertidal zone of Japanese waters. We also explored the phylogenetic position of the new taxa based on partial sequences of the nuclear 18S rRNA and 28S rRNA genes. Proschizorhynchella quadricaudata sp. nov. is characterized by (i) proboscis lips with a row of glands; (ii) a simple cone-shaped stylet; and (iii) a caudal end with four finger-shaped projections. Cheliplana izuensis sp. nov. can be distinguished from its congeners by (i) two strong hooks with bifurcate tips, encircling the distal part of the spiny cirrus; (ii) the fact that the proximal 20% of the cirrus length is unarmed; (iii) proboscis' sidepieces lacking needles; (iv) paired seminal vesicles; and (v) the presence of a vagina. The phylogenetic analyses support the position of P. quadricaudata sp. nov. within Schizorhynchidae and the position of C. izuensis sp. nov. in a clade containing all species of Cheliplana within Cheliplanidae.