Elasmopus, Costa, 1853

Nakamura, Yasuhiro, Nakano, Takafumi, Ota, Yuzo & Tomikawa, Ko, 2019, A new species of the genus Elasmopus from Miyako Island, Japan (Crustacea: Amphipoda: Maeridae), Zootaxa 4544 (3), pp. 395-406 : 404

Key to the species of Elasmopus (male) recorded from Japanese and adjacent waters

1 Posterior margin of bases of pereopods 6 and/or 7 castelloserrate............................................... 2

- Posterior margin of basis of pereopods 6 and 7 smooth........................................................ 3

2 Setae on posterior margin of propodus of gnathopod 2 shorter than width of propodus; posterodistal corner of basis of pereopod 6 strongly produced..................................................................... E. pectenicrus

- Setae on posterior margin of propodus of gnathopod 2 longer than width of propodus; posterodistal corner of basis of pereopod 6 not produced............................................................................ E. nanshaensis

3 Telson longer than width............................................................................... 4

- Telson shorter than width............................................................................... 5

4 Foremost medial tooth on palm of propodus of male gnathopod 2 not exceeding palmar margin; distomedial shelf of propodus of male gnathopod 2 with 2 medial and 4 lateral robust setae; posterodistal setae on propodi of pereopods 5–7 longer than length of dactyli; basis of male pereopod 7 length 1.5 × width........................................... E. rapax

- Foremost medial tooth on palm of propodus of male gnathopod 2 exceeding palmar margin; distomedial shelf of propodus of male gnathopod 2 with 4 medial and 6 lateral robust setae; posterodistal setae on propodi of pereopods 5–7 shorter than length of dactyli; basis of male pereopod 7 length 1.3 × width................................................... E. nkjaf

5 Posterior margin of basis of pereopod 7 with long setae.............................................. E. hooheno

- Posterior margin of basis of pereopod 7 without long setae................................................... 6

6 Posteroventral corner of epimeral plate 3 pointed; anteromarginal setae on merus of pereopod 7 shorter than width of merus; distal part of telson lobes deeply concave......................................................... E. japonicus

- Posteroventral corner of epimeral plate 3 rounded; anteromarginal setae on merus of pereopod 7 longer than width of merus; distal part of telson lobes shallowly concave....................................................... E. koreanus