Maera, Leach, 1814

Ariyama, Hiroyuki, Kodama, Masafumi & Tomikawa, Ko, 2020, Species of the Maera-clade collected from Japan. Part 4: addenda to genera Maera Leach, 1814 and Quadrimaera Krapp-Schickel & Ruffo, 2000, with revised keys to Japanese species of the clade (Crustacea: Amphipoda: Maeridae), Zootaxa 4885 (3), pp. 336-352 : 351

Key to adult females of Japanese species of the Maera -clade.

Maera sagamiensis Ariyama, 2020 and Quadrimaera gotoensis Ariyama, 2019 are not included owing to the lack of female information.

1. Gnathopod 2, anterior margin of dactylus bearing many setae.................................................. 2

- Gnathopod 2, anterior margin of dactylus with single seta..................................................... 3

2. Body very large (maximum BL:> 50 mm), gnathopod 2 palm defined by tooth bearing strong robust seta............................................................................................ Maera loveni ( Bruzelius, 1859)

- Body small (maximum BL: about 16mm), gnathopod 2 palm defined by tooth bearing small robust seta.................................................................................................. Maera denticoxa sp. nov.

3. Pereopods 3–7 dactyli bifid............................................................................. 4

- Pereopods 3–7 dactyli simple............................................................................ 7

4. Gnathopod 2 palm rounded, telson lobes incised..................................... Quadrimaera angulata sp. nov.

- Gnathopod 2 palm almost straight, telson lobes truncate....................................................... 5

5. Pereopod 5 basis subrectangular, posterodistal corner scarcely lobate............. Quadrimaera quqdrimana ( Dana, 1853)

- Pereopod 5 basis ovate, posterodistal corner roundly lobate.................................................... 6

6. Pereopod 6, posterior margin of basis setose.................................. Quadrimaera setibasis Ariyama, 2019

- Pereopod 6, posterior margin of basis not setose........................... Quadrimaera pacifica ( Schellenberg, 1938)

7. Uropod 3, tips of both rami pointed......................................... Austromaera ariakensis Ariyama, 2019

- Uropod 3, tips of both rami truncate...................................................................... 8

8. Uropod 3 rami long, about 3 times length of peduncle............................ Meximaera mooreana ( Myers, 1989)

- Uropod 3 rami relatively short, 1 – 2 times length of peduncle................................................... 9

9. Gnathopod 2 palm transverse, without robust setae; mandibular palp article 1 with distal tooth....................... 10

- Gnathopod 2 palm slightly or moderately oblique, with many robust setae; mandibular palp article 1 lacking distal tooth.. 11

10. Uropod 3 longer than uropod 2, basis of pereopod 5 subovate.................... Maeropsis okinawensis Ariyama, 2018

- Uropod 3 shorter than uropod 2, basis of pereopod 5 subrectangular.............. Maeropsis serratipalma ( Nagata, 1965)

11. Palm of gnathopod 2 moderately oblique (angle of palmar corner: 115–130°)..................................... 12

- Palm of gnathopod 2 slightly oblique (angle of palmar corner: 90–100°)......................................... 13

12. Coxa 1 anteroventral corner produced acutely, distal robust setae of telson short (ca. 20% of telson length).................................................................................... Orientomaera obliquua Ariyama, 2018

- Coxa 1 anteroventral corner rounded, distal robust setae of telson long (ca. 45% of telson length)......................................................................................... Orientomaera rotundicoxa Ariyama, 2018

13. Palm of gnathopod 2 with two distinct teeth.................................... Orientomaera incisa Ariyama, 2020

- Palm of gnathopod 2 with several blunt teeth.............................................................. 14

14. Posterior margin of pereopod 6 basis almost straight, body color bluish pale pink................................................................................................... Orientomaera brevispina ( Kim & Kim, 1991)

- Posterior margin of pereopod 6 basis convex, body color light crimson............ Orientomaera decipiens Ariyama, 2018