Orchestia aestuarensis Wildish, 1987

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 : 227-229

Orchestia aestuarensis Wildish, 1987

( Figs 20–21 )

Orchestia aestuarensis Wildish, 1987 , 572, figs 1–4, fig. 5d, fig. 6, tables 1–3.

Type locality. Wouldham Marsh , Medway Estuary, Kent, United Kingdom, near mean high water mark of neap tides .

Description of adult male (15 mm).

Head. Eyes of moderate size. Antenna 1 short, not reaching beyond peduncular article 4 of antenna 2; accessory flagellum absent; primary flagellum with 6 articles. Antenna 2 peduncular article 5, 1.7 × length of peduncular article 4; flagellum longer than combined length of peduncular articles 4 and 5, with 19 articles, final article cone shaped, with terminal cluster of imbricated setae. Labrum without epistome. Mandible left lacinia mobilis with 4 cusps. Maxilliped palp article 2 with distomedial lobe.

Pereon. Gnathopod 1 subchelate, coxa smaller than that of coxa 2; posterior margin of carpus and propodus each with lobe covered in palmate setae; propodus length to carpus length 1:1.6; propodus strongly triangular; dactylus shorter than palm. Gnathopod 2 subchelate; basis 2.1 × as long as broad; merus posterior margin with 2 short setae; propodus strongly triangular, distal width 1.7 × proximal width. Pereopods 3–7 cuspidactylate, Pereopods 3–4 dactylus relatively slender, acute. Pereopod 4 dactylus thickened proximally with a notch midway along posterior margin. Pereopod 5 basis subovoid. Pereopod 7 basis posterior margin smooth; merus elongate, weakly

triangular, 2 × as wide distally as proximally; carpus irregular, anterior margin strongly convex, posterior margin irregularly concave, 1.5 × as long as broad; carpus a little longer than merus; propodus and carpus subequal in length.

Pleon. Epimeron 3 posterior margin weakly crenulate. Uropod 1 peduncle longer than rami, without distolateral robust seta; rami subequal. Uropod 2 peduncle subequal in length with rami, rami subequal; exopod with 2 marginal robust setae; endopod with 3 marginal robust setae. Uropod 3 peduncle only a little longer than broad; ramus 1.8 × as long as broad, 0.7 × length of peduncle, outer margin with 3 robust setae. Telson with about 8 apical robust setae on each side.

Female (sexually dimorphic characters). Gnathopod 2 mitten-shaped; Pereopod 7 slender, merus and carpus unexpanded.

Habitat. High water neap in Estuaries.

Remarks. This species is very close to O. mediterranea Costa but differs in the dactyls of pereopods 3–4 that are very elongate and slender in O. aestuarensis , but short and stout in O. mediterranea .

Distribution. United Kingdom. Medway Estuary, Kent ( Wildish 1987); Tamar Estuary, Devon ( Wildish 1987).

Figures

FIGURE 20. Orchestia aestuarensis Wildish, 1987, Medway Estuary, Kent, England, redrawn from Wildish, 1987).

FIGURE 21. Orchestia aestuarensis Wildish, 1987, Medway Estuary, Kent, England (redrawn from Wildish 1987).