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) Author Ariyama, Hiroyuki Osaka Museum of Natural History, Nagai Park, Higashi-Sumiyoshi, Osaka 546 - 0034 Japan. Author Kodama, Masafumi International Coastal Research Center, Atmosphere and Ocean Research Institute, The University of Tokyo, 1 - 19 - 8 Akahama, Otsuchicho, Iwate 028 - 1102, Japan. mkodama @ aori. u-tokyo. ac. jp; https: // orcid. org / 0000 - 0002 - 0889 - 5625 Author Tomikawa, Ko Graduate School of Humanities and Social Sciences, Hiroshima University, 1 - 1 - 1 Kagamiyama, Higashihiroshima, Hiroshima 739 - 8524, Japan. tomikawa @ hiroshima-u. ac. jp; https: // orcid. org / 0000 - 0003 - 1521 - 9016 text Zootaxa 2020 2020-11-26 4885 3 336 352 journal article 9435 10.11646/zootaxa.4885.3.2 3ff96650-b8c7-40cb-a557-3f4e7a9d235d 1175-5326 4296670 45D0CE12-9E4D-4939-B3AB-A34717B3B104 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