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 : 350

Key to adult males of Japanese species of the Maera -clade (revised).

Quadrimaera angulata sp. nov. is not included because the male is unknown.

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

- Gnathopod 2, anterior margin of dactylus with single seta..................................................... 4

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 10–16mm), gnathopod 2 palm defined by tooth bearing small robust seta.............. 3

3. Small notches present on coxae 1–6.................................................... Maera denticoxa sp. nov.

- Small notches present on coxae 1–3............................................ Maera sagamiensis Ariyama, 2020

4. Pereopods 3–7 dactyli bifid............................................................................. 5

- Pereopods 3–7 dactyli simple............................................................................ 8

5. Gnathopod 2 palm with 2 excavations in middle.............................. Quadrimaera quqdrimana ( Dana, 1853)

- Gnathopod 2 palm with single excavation in middle.......................................................... 6

6. Excavation on gnathopod 2 palm quadrate................................... Quadrimaera gotoensis Ariyama, 2019

- Excavation on gnathopod 2 palm rounded.................................................................. 7

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

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

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

- Uropod 3, tips of both rami truncate...................................................................... 9

9. Gnathopod 2 basis wide; uropod 3 rami long, about 3 times length of peduncle........ Meximaera mooreana ( Myers, 1989)

- Gnathopod 2 basis ordinary; uropod 3 rami relatively short, 1 – 2 times length of peduncle........................... 10

10. Gnathopod 2 palm transverse, without robust setae; mandibular palp article 1 with distal tooth....................... 11

- Gnathopod 2 palm slightly or moderately oblique, with many robust setae; mandibular palp article 1 lacking distal tooth.. 12

11. 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)

12. Palm of gnathopod 2 moderately oblique (angle of palmar corner: 115–130°)..................................... 13

- Palm of gnathopod 2 slightly oblique (angle of palmar corner: 90–105°)......................................... 14

13. 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

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

- Palm of gnathopod 2 with several blunt teeth.............................................................. 15

15. 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