(Fig. 2)
Eupagurus trigonocheirus Stimpson, 1858: 249; 1907: 211, pl. 26 fig. 2.
Pagurus trigonocheirus. — Makarov, 1938b: 109; 1962: 109.— Kim, 1973: 234, text-fig. 55, pl. 6 fig. 35.— McLaughlin, 1974: 233, figs. 59, 60, pl. 1 figs. 1, 2.— Miyake, 1982: 126, pl. 42 fig. 4.— Asakura, 2006: 42, figs. 48–50.
Material examined. 2 males, 3 females, 4 juveniles (LEMMI), Russian Far East, Sea of Japan, Peter the Great Bay, opposite the Vostok Bay, depth 60–100 m, sandy-gravel bottom, Agassiz trawl, coll. I. Marin, 29 May 2014; 2 males, 3 females, 2 juveniles (LEMMI), Russian Far East, Sea of Japan, Peter the Great Bay, opposite the Ussuri Bay, depth 85 m, sandy-gravel bottom, Agassiz trawl, coll. I. Marin, 30 May 2014.
Morphological diagnostic features. The species can be clearly separated from the related congeners (Pagurus rathbuni (Benedict, 1892), Pagurus townsendi (Benedict, 1892), Pagurus dalli (Benedict, 1892) and Pagurus pubescens Krøyer, 1838) by the presence of a prominent concavity and well-marked crest on the minor (left) pereiopod I (cheliped) (Fig. 2 c, d), the absence of bristle setae on the distolateral margin of carpus of major (right) pereiopod I (see Fig. 2 e) and bright white spots on the carpo-propodal articulation of the chelipeds and ambulatory pereiopods in living specimens (Fig. 2 a).
Records from the Sea of Japan. Sublittoral, 50– 150 m. North of Mikuni (Fukui-ken), north and north-east of Noto (Yokoya 1933), Oshoro (Igarashi 1970) and Toyama Bay, Japan (Asakura 2006); east coast of Korea (Kim, 1973); the Peter the Great Bay, Russia (present study) (Fig. 1).
General Distribution. Subtidal to 497 m. Bering Sea, the Chukchi Sea, Aleutian Islands and Kamchatka coastline, Kuril Islands, Sakhalin, the Sea of Japan, Korea, the Pacific coasts of northern Japan southward to Inubo-zaki (Makarov 1938b, 1962 (as P. pubescens)); McLaughlin 1974; Miyake 1982; Asakura 2006; Komatsu & Komai 2009; Komai et al. 2015). Note that such wide distributions need to be verified for the reasons discussed above.