Platorchestiinae subfam. nov. (Amphipoda, Senticaudata, Talitridae) with the description of three new genera and four new species Author Lowry, J. K. Author Myers, A. A. 0000-0003-3256-2123 School of Biological, Earth and Environmental Sciences, University College Cork, Cork Enterprise Centre, Distillery Fields, North Mall, Cork, Ireland. bavayia @ gmail. com; https: // orcid. org / 0000 - 0003 - 3256 - 2123 bavayia@gmail.com text Zootaxa 2022 2022-02-17 5100 1 1 53 journal article 20608 10.11646/zootaxa.5100.1.1 cabdbbb1-1226-4c2e-b90b-fae0742b5091 1175-5326 6127681 F42DAC62-0E30-442E-A375-87FC02B2CC99 Yamatorchestia Takahashi & Morino, 2021 Nipponorchestia Morino & Miyamoto, 2015: 2 (in part). Yamatorchestia Takahashi & Morino, 2021:11 . Type species. Nipponorchestia nudiramus Morino & Miyamoto, 2015 , original designation. Type locality. Ashu , Research Forest ( Kyoto University ), Kyoto , Japan . Included species. Yamatorchestia includes 1 species: Y. nudiramus ( Morino & Miyamoto, 2015 ) . Category. Mascupod. Ecological type . Forest-hoppers (non-substrate-modifying talitrids). Habitat. Terrestrial, from under litter or moist soils of coastal habitats including grasslands and forests, occasionally from near supralittoral zones. Size. Male, 7.4 mm , female, 7.7 mm . Diagnostic description ( male ). Based on Morino & Miyamoto (2015) and Takahashi & Morino (2021) . Head. Antenna 1 short, not reaching midpoint of antenna 2 peduncular article 5; flagellum with 4 articles, geniculated between articles 2 and 3, article 3 longest. Antenna 2 peduncular articles slender ; article 3 without plate or process ventrally. Mandible left lacinia mobilis 4-cuspidate . Labium without inner lobes, or with possible vestigial inner lobes. Maxilliped palp slender ; article 2 with distomedial lobe; article 4 reduced, button-shaped. Pereon. Gnathopod 1 sexually dimorphic; subchelate; coxa slightly smaller than coxa 2; posterior margin of carpus and propodus each with lobe covered in palmate setae; propodus anterior margin with 2 groups of robust setae, ‘subtriangular’ with well-developed posterodistal lobe, palm transverse; dactylus apparently simplidactylate. Gnathopod 2 subchelate; propodus palm acute; propodus palm evenly rounded; without palmar sinuses; without proximal spine or thumb defining palm; without large projection near dactylar hinge; dactylus slightly curved, longer than palm, recurved distally . Pereopods 3–7 dactyli bicuspidactylate. Pereopod 4 subequal or slightly shorter than pereopod 3; carpus similar in length to that of pereopod 3; dactylus amplidactylate (weakly pinched), similar to pereopod 3 dactylus, not thickened proximally or notched. Pereopod 6 subequal in length to pereopod 7, not incrassate; distally; coxal gill of pereopod 6 with leaf-shaped lobe ; basis moderately expanded; male merus and carpus not expanded. Pereopod 7 not incrassate; basis broadly expanded; posterior margin smooth or minutely serrate margin with numerous small slender setae, posterodistal lobe produced downwards almost to merus, triangular, produced downwards almost to merus; merus unexpanded; carpus unexpanded; subrectangular; carpus shorter than propodus; propodus without large distal tuft of setae. Oostegites (female) setae with simple smooth tips. Pleon. Pleopods all reduced . Epimeral plates without slits. Uropod 1 peduncle distolateral robust seta present; exopod without marginal robust setae; endopod with marginal robust setae in 1 row. Uropod 2 exopod with marginal robust setae in 1 row; endopod with marginal robust setae in 1 row. Uropod 3 ramus shorter than peduncle. Telson apically incised, with 2 robust setae per lobe . Remarks . Yamatorchestia is the only platorchestiine with only 2 robust setae per lobe on the telson. Based on the slender second antenna, pereopod 4 dactylus unmodified, similar to that of pereopod 3 and reduced pleopods Yamatorchestia is similar to the Hawaiian terrestrial genera Laniporchestia and Pickorchestia . It shares a gnathopod 2 palm with no sinuses with Laniporchestia , but differs in the gnathopod 2 dactylus which is short and recurved (attenuated in Laniporchestia ). Yamatorchestia differs from Pickorchestia in having no sinuses on the palm of gnathopod 2, and in having a short recurved dactylus (not modified, blunt in Pickorchestia ). Distribution. Japan . Central and south-west Honshu.