1 Posterior margin of epimeral plate 3 crenulated or denticulated; outer plate of maxilliped almost reaching distal margin of palp article 3............................................................................................................................................................................ O. tridentata
- Posterior margin of epimeral plate 3 smooth; outer plate of maxilliped not reaching distal margin of palp article 3...................... 2
2 Dactylus of gnathopod 1 short, nearly straight, posterior margin dentate; palm of propodus of gnathopod 1 straight, lined with close-set “palisade” robust setae; rami of uropod 3 without marginal setae............................................................... O. odontochela
- Dactylus of gnathopod 1 large, strongly curved, posterior margin smooth; palm of propodus of gnathopod 1 concave, with few slender setae.......................................................................................................................................................................................3
3 Lacinia mobilis of left mandible developed; posterior lobe of coxa 5 weakly developed; inner ramus of uropod 2 with robust setae ......................................................................................................................................................................................... O. eschrichti
- Lacinia mobilis of left mandible vestigial; posterior lobe of coxa 5 well developed; inner ramus of uropod 2 without robust setae................................................................................................................................................................ O. takafuminakanoi sp. nov.