Orchestia Leach, 1814

Myers, Alan A. & Lowry, James K., 2020, A revision of the genus Orchestia Leach, 1814 with the reinstatement of O. inaequalipes (K. H. Barnard, 1951), the designation of a neotype for Orchestia gammarellus (Pallas 1776) and the description of three new species (Crustacea: Amphipoda: Talitridae Talitrinae), Zootaxa 4808 (2), pp. 201-250 : 207-208

Orchestia Leach, 1814

Gammarellus ( Orchestia ) Herbst, 1793: 106. Talitrus (in part.).― Bosc, 1802: vol. 1, 78; vol. 2, 148.― Latreille, 1802: 38. Orchestia .―Leach, 1813/14: 402.― Stebbing, 1888: 602, 1678.―Sars, G.O. 1890: 24.― Della Valle, 1893: 494.― Stebbing,

1906a: 530.― Chevreux & Fage, 1925: 272.― Shoemaker, 1942: 17.― Hurley, 1956: 149 (in part).― Bousfield & Holthuis,

1969: 105, 110.―J.L. Barnard, 1969: 470 (in part).― Lincoln, 1979: 212 (in part).― Bousfield, 1982: 22.― Bellan-Santini,

1993: 742. Scamballa (part.) White, 1847: 86.

Type species. Oniscus gammarellus Pallas, 1776 , monotypy.

Included species. Orchestia aestuarensis Wildish, 1987 ; O. forchuensis sp. nov.; O. gammarellus (Pallas, 1766) ; O. inaequalipes (K.H. Barnard, 1951) ; O. magnifica Vecchi. 1931 ; O. mediterranea Costa, 1857 ; O. montagui ( Audouin, 1826) ; O. perezi sp. nov.; O. tabladoi sp. nov.; O. xylino Lowry & Fanini, 2013 .

One species, O. guernei ( Chevreux, 1889) , remains a dubious species.

Ecological type. Beach-hopper, marsh-hopper.

Habitat. Shore-dwelling and inland coastal wetlands.

Category. Mascupod.

Size. 12–20 mm. Sexual dimorphism present.

Diagnostic description.

Head. Eye medium (1/5–1/3 head length), or large (greater than 1/3 head length). Antenna 1 short, not reaching midpoint of peduncular article 5 of antenna 2. Antenna 2 peduncular articles slender or slightly incrassate (expanded); article 3 without plate or process ventrally. Labrum epistome without robust setae; median groove without robust setae. Mandible left lacinia mobilis 4-cuspidate. Maxilliped palp article 2 with distomedial lobe; article 4 reduced, button-shaped.

Pereon. Pereonites without transverse ridges. Gnathopod 1 sexually dimorphic; subchelate; posterior margin of carpus and propodus each with lobe covered in palmate setae; propodus ‘subtriangular’ with well-developed posterodistal lobe. Gnathopod 2 subchelate; posterior margin of merus, carpus and propodus each without lobe covered in palmate setae; female merus posterodistal lappet absent; propodus palm acute; dactylus not modified distally, blunt, shorter than posterior margin of propodus. Pereopods 3–7 bicuspidactylate. Pereopod 4 dactylus thickened proximally with notch midway along posterior margin. Pereopod 5 dactylus long, slender, dactylus not inflated. Pereopod 6 not sexually dimorphic; basis expanded. Pereopod 7 sexually dimorphic; merus broad, carpus expanded.

Pleon. Pleonites 1–3 without dorsal spines. Oostegites (female) setae with simple smooth tips. Pleopods 1–3 all well-developed. Epimera 1–3 slits absent. Uropod 1 male exopod not sexually dimorphic, peduncle distolateral robust seta present or absent; rami without apical spear-shaped setae; endopod with marginal robust setae in 1 or 2 rows; exopod with marginal robust setae in one row. Uropod 2 rami without apical spear-shaped setae; exopod with marginal robust setae in 1 row; endopod with marginal robust setae in 1 row or 2 rows. Uropod 3 ramus subequal, longer or shorter than peduncle. Telson apically incised, with dorsomarginal and apical robust setae, with 3 to at least 10 marginal and apical robust setae per lobe.

Discussion. We acknowledge the molecular studies of Villacorta et al. (2008) and Pavesi et al. (2015) that infer that Orchestia is not monophyletic. However, we have been unable to offer any morphological support for this assertion. As we are unable to diagnose distinct genera from within Orchestia sensu stricto (as recognised herein) we have no option, but to retain the monophyly of Orchestia .

Orchestia is similar to the terrestrial European genus Cryptorchestia and the Mediterranean/western Atlantic coastal genus Speziorchestia . It differs from both in having sexually dimorphic seventh pereopods. Orchestia is also similar to the North Pacific genus Bulychevia from which it differs in having simple smooth-tipped setae on the female oostegites (curl-tipped in Bulychevia Lowry & Myers, 2019 ).

Orchestia grillus ( Bosc, 1802) , O. stephenseni Cecchini, 1928 and O. tucurauna Müller, 1864 were moved to Speziorchestia Lowry & Myers, 2019 and Orchestia ghigii Vecchi, 1929 is synonymised with Speziorchestia stephenseni .