Orchestia inaequalipes (K.H. Barnard, 1951 )

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 : 234-237

Orchestia inaequalipes (K.H. Barnard, 1951)

( Figs 26–28 )

Talorchestia inaequalipes K.H. Barnard, 1951: 705 , fig. 5 a, b.

Orchestia gammarella .― Griffiths, 1976: 79 (key), figs 49, 50A, 52H.

Orchestia gammarellus .― Diemer et al., 2016: 203, figs 1–3, table 1.

Type locality. Langebaan , Saldanha Bay, South Africa .

Material Studied. 8 males, 7 females, Milnerton Estuary , Cape Town, South Africa, 21.09.2018, coll. C. Griffiths.

Description of adult male (19 mm).

Head. Eyes of moderate size. Antenna 1 short, just reaching peduncular article 4 of antenna 2. Antenna 2 peduncular article 5 1.5 × length of peduncular article 4; flagellum subequal in length with combined length of peduncular articles 4 and 5, with about 18 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, article 4 rudimentary.

Pereon. Gnathopod 1 subchelate, coxa smaller than that of coxa 2; posterior margin of carpus and propodus each with strong lobe covered in palmate setae; carpus slender with strongly protrubent palmate lobe; propodus length to carpus length 1:1.4; propodus strongly triangular; dactylus shorter than palm. Gnathopod 2 subchelate;

basis length 2.4 × as long as broad, merus posterior margin without setae; propodus subovoid, distal width 1.8 × proximal width; dactylus weakly convex. Pereopods 3–4 dactylus relatively slender, acute. Peropod 4 dactylus thickened proximally with a notch midway along posterior margin. Pereopod 5 basis subround, Pereopod 7 basis posterior margin distinctly serrate; merus elongate, weakly to strongly triangular, 2–3 × as wide distally as proximally; carpus subovoid becoming subrectangular in large males, about 1.3 × as long as broad; subequal in length with merus; propodus elongate, 1.3 × length of carpus.

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 2 marginal robust setae and 2 robust setae on inner face. U3 peduncle only a little longer than broad, 1.5 × length of ramus, ramus slender 2.7 × as long as broad, outer margin with 3 slender setae. Telson with 6 or less relatively slender robust setae on each side.

Female. Gnathopod 2 basis slender, 2.6 × as long as broad, anterior margin evenly convex; carpus 1.8 × length of propodus. Pereopod 7 stout, basis posterior margin distinctly serrate, merus and carpus unexpanded.

Habitat. Supralittoral among decaying algae.

Remarks. Initially regarded as an endemic species, Talorchestia inaequalipes Barnard, 1951 was considered to be synonymous with Orchestia gammarellus by Griffiths (1974, 1975).

Orchestia inaequalipes shares with the other southern hemisphere species O. perezi and O. tabladoi , a telson that has only 6 or less relatively long and slender setae per lobe (more than 7 stouter setae in northern hemisphere species) and a uropod 3 with the peduncle one and a half times the length of the ramus (subequal in northern hemisphere species except in O. montagui ). It differs from both O. perezi and O. tabladoi in the slender basis of the female gnathopod 2 (proximally broad in O. perezi and O. tabladoi ). It differs from O. perezi in the much more strongly developed palmate lobes on the male gnathopod 1. It differs from O. tabladoi in the more slender carpus of the male gnathopod 1, in the more elongate carpus of the male pereopod 7 that becomes subrectanglar in large males (almost as broad as long and subovoid in O. tabladoi )

In addition to the form of the telson and uropod 3 mentioned above, Orchestia inaequalipes differs from O. gammarellus in the more elongate carpus of the male gnathopod 1 with more narrowly produced posterodistal palmate lobe, in the subround basis of pereopod 5 (subovoid in O. gammarellus ), and in the strongly serrate basis of pereopod 7 (weakly serrate in O. gammarellus ). In large adult males the carpus of pereopod 7 becomes subrectangular but is subtriangular in O. gammarellus .

Distribution. South Africa: Langebaan (K.H. Barnard 1951); Table Bay, Knysna Estuary ( Griffiths 1974); Milnerton Estuary (Griffiths pers. com.); False Bay, south-east Coast, East London ( Mead et al. 2011b).

Figures

FIGURE 26. Orchestia inaequalipes (K.H. Barnard, 1951), Millerton Estuary, Cape Town, South Africa.

FIGURE 27. Orchestia inaequalipes (K.H. Barnard, 1951), Millerton Estuary, Cape Town, South Africa.

FIGURE 28. Orchestia inaequalipes (K.H. Barnard, 1951), Millerton Estuary, Cape Town, South Africa.