Yamatorchestia Takahashi & Morino, 2021

Lowry, J. K. & Myers, A. A., 2022, Platorchestiinae subfam. nov. (Amphipoda, Senticaudata, Talitridae) with the description of three new genera and four new species, Zootaxa 5100 (1), pp. 1-53 : 45

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.