Revision of the millipede genus Xystodesmus, with reference to the status of the tribe Xystodesmini (Diplopoda: Xystodesmidae)

On the basis of morphometrics and geographic distribution, we revise Xystodesmus martensii Peters and its related forms in Japan, which had been recognized as ten species belonging to five genera. In delimitation of species, first we sought the biggest pheno-geographic units based on the dendrogram from a cluster analysis and geographic distribution; a pheno-geographic unit is defined as an aggregation of populations being phenetically closely similar and geographically closely distributed to each other. Then, we decided whether each unit was warranted as a species. As a result, we propose that these forms constitute a single genus Xystodesmus comprising six species including one new species. The newly defined Xystodesmus is characterized by high variation in gonopod morphology and conservative coloration, body form and size. The status of some populations is still uncertain because of lack of material. The tribe Xystodesmini, to which Xystodesmus belongs, and the tribe Harpaphini are so similar that we could not warrant their separation. We propose the following new synonymies: the tribe Harpaphini with the tribe Xystodesmini; Phrurodesmus Takakuwa and Nikkonus Chamberlin and Wang with Xystodesmus; Xystodesmus scabra Verhoeff, Rhysodesmus tuberculatus Takakuwa, Rh. ikaoensis Takakuwa, and Rh. kitazawai Miyosi, with X. martensii; Phrurodesmus kinshaensis Murakami with X. gracilipes (Takakuwa). Riukiaria shirozui Takakuwa, Rh. serrulatus Miyosi, and P. gracilipes Takakuwa, are transferred to Xystodesmus. We describe X. tokaiensis as a new species.