Two new subterranean species of Pseudocrangonyx Akatsuka & Komai, 1922 (Amphipoda: Crangonyctoidea: Pseudocrangonyctidae), with an insight into groundwater faunal relationships in western Japan

Abstract

Amphipods belonging to the crangonyctoid genus Pseudocrangonyx Akatsuka & Komai, 1922 constitute a major component of the subterranean environments in east Asia. The true species diversity of this group has been unsettled due to the lack of molecular data for P. shikokunis Akatsuka & Komai, 1922 and P. kyotonis Akatsuka & Komai, 1922 and the taxonomic status of the misidentified populations of these two species. The status of the misidentified populations is herein clarified. Morphological comparisons among the specimens of these populations and the name-bearing types of P. shikokunis and P. kyotonis demonstrate the two are distinctive species. Phylogenetic analyses using partial sequences of nuclear 28S rRNA and histone H3, mitochondrial cytochrome c oxidase subunit I, and 16S rRNA genes also confirm that each of the two populations represents a unique clade within the species of Pseudocrangonyx. Accordingly, the population indigenous to the limestone caves in western Japan, which was previously identified as P. shikokunis, is described as P. akatsukai n. sp., and that reported as P. kyotonis from central Japan is described as P. komaii n. sp. The phylogenetic relationships within P. akatsukai n. sp. and an unidentified Pseudocrangonyx species elucidate the complex stygofaunal relationships in western Japan (western Honshu, Shikoku, and Kyushu). A key to Pseudocrangonyx species is also provided.