Two new species of Rhabdocoela (Polycystididae and Trigonostomidae from China

Two new species of Rhabdocoela, namely Alcha sinensis n. sp. (Polycystididae) and Trigonostomum sinensis n. sp. (Trigonostomidae), were discovered from the intertidal zone of eastern Shenzhcn City, China. For A. sinensis n. sp., the stylet consists of two symmetrical triangular plates and one lamellar plate. All three plates are jagged at their posterior ends. The anterior end of the stylet connects to a thick muscular layer, which causes its movement. For T sinensis n. sp., the copulatory organ consists of a long-tubular sty let and two T-shaped plates (plate I and plate II). The sty let bends 120 degrees at 25% of its length from the base and extends straight distally. Two T plates are connected to each other and surround the stylet. Plate I is hook-shaped at its distal end, and plate II has a similar length but only half the width of plate I. The phylogenetic (18S rDNA and 28S rDNA) results also support the establishment of these two new species. On the basis of the molecular phylogeny and morphology of the copulatory organ and bursa appendage, we propose a new categorization of the species of Trigonostomum.