The grapsoid crab Xenograpsus testudinatus N. K. Ng, Huang & Ho, 2000, originally described from northern Taiwan, is recorded for the first time from shallow water thermal vents (3–5 m) in Kagoshima Prefecture, Japan. The Japanese material of X. testudinatus differs slightly from the Taiwanese material in the form of the frontal margin of the carapace, as well as the structure of the chelae, ambulatory legs, and male abdomen, but none of the differences is regarded as significant at the species-level. Genetic studies with mitochondrial cytochrome oxidase I (COI) gene support its conspecificity with X. testudinatus.