Serène, 1964
The species seems to be intermediate between Sakaina yokoyai (Glassell) and Sakaina asiatica (Sakai). It is apparently larger than Sakaina asiatica, but smaller than Sakaina yokoyai. In Sakaina japonica, as well as in Sakaina asiatica, the carapace is transversely suboval and its antero-lateral borders are subparallel with each other - each lined with a narrow belt of short pubescence, extending from the outer orbital angle towards the junction of the antero- and postero-lateral borders. In Sakaina yokoyai, the carapace is strikingly convex at the anterior hepatic borders, and the posterior halves of the antero-lateral borders are apparently convergent. No belt of pubescence is to be seen along the antero-lateral borders. (Sakai, 1965)
Type locality: Misaki, Sagami Bay, Japan.
Range: Japan - Misaki, Sagami Bay (Serène, 1964), Sagami Bay (Sakai, 1965b), Sagami Bay and Kii Nagashima (Sakai, 1976a), Amakusa (Yamaguchi et al., 1976), Kumano-nada (Sakai, 1983), Esashi, Ehime and Amakusa (Takeda et al., 1991), Oshoro, Kikonai and Esashi (Komai et al., 1992), Ashizuri-misaki (Muraoka, 1998), off Takehara, Seto Inland Sea (Takeda et al., 2000); shallow waters.