Quasimelita Jarrett & Bousfield, 1996 ( Jarret & Bousfield, 1996: 36 )

Labay, Vjacheslav S., 2014, Review of amphipods of the Melita group (Amphipoda: Melitidae) from the coastal waters of Sakhalin Island (Far East of Russia). II. Genera Quasimelita Jarrett & Bousfield, 1996 and Melitoides Gurjanova, 1934, Zootaxa 3869 (3), pp. 237-280 : 240

Genus Quasimelita Jarrett & Bousfield, 1996 ( Jarret & Bousfield, 1996: 36)

Melita Stebbing, 1906: 421 (part).— Gurjanova, 1951: 748, 751 (part).— Karaman, 1981: 41 (part).— Barnard & Barnard, 1983: 664 (part).

Abludomelita Karaman, 1981: 40 (part).

Type species. Melita quadrispinosa Vosseler, 1889: 157 .

Species. Including the new species described here, Quasimelita contains five species in the North Pacific ( Jarret & Bousfield 1996, new data): Q. formosa ( Murdoch, 1885) , Q. quadrispinosa ( Vosseler, 1889) , Q. jarettii sp. nov., Q. serraticoxae sp. nov. and Q. tolyza sp. nov. Q. formosa and Q. quadrispinosa are widely distributed across the Siberian and Canadian Arctic region and in the North Pacific region to Japan. Q. abyssorum ( Stephensen, 1944) was described only from North Atlantic and near Arctic (Palerud, Gulliksen, Brattegard, Sneli, J.-A. & Wim Vader, 2004; Stephensen, 1944; Vosseler, 1889).

Diagnosis (from Jarret & Bousfield 1996, with additions). Pereon segments without dorsal teeth and denticles. Pleon toothed to smooth dorsally. Urosome segment 1 usually with dorsal tooth (or one large central tooth and two lateral small teeth). Urosome 2 with dorsal teeth (usually paired) and with single strong seta on each side. Head, anterior lobe usually rounded (or truncated), inferior antennal sinus broadly notched. Antenna 1 regular, peduncular segment 3 short; antenna 2 slightly or much shorter than antenna 1.

Upper lip shallow notched. Lower lip regular, inner lobes large. Mandible, raker setae row short, with numerous blades (7–13+); left lacinia 4-dentate, right lacinia 3-dentate; incisor irregulary dentate, palp segment 1 short, with acute medial process or not. Maxilla 1, inner plate triangular, usually weakly setose medially; outer plate with 9 apical tooth setae (Watling type III.1) ( Watling 1989); palp segment 1 with lateral setae; segment 2 apically spinose and setose. Maxilla 2, inner plate usually with few facial setae, submarginally positioned. Maxilliped, inner plate tall; outer plate medium large, broad, apical margin setose; palp segment 2 stout; dactylus short.

Coxal plates 1–4 medium to shallow and may decrease in size and depth posteriorly. Coxae 1–3, lower margin rounded or squared, hind corner lacking cusp. Coxa 4 small, posterior proximal excavation weak or lacking. Pereopods 1 and 2 conspicuously sexually dimorphic. Pereopod 1 small, weakly sexually dimorphic; propodus shorter than carpus, margins strongly setose; palm and dactylus short. Pereopod 2 (male), carpus large, with broadly setose posterior margin and densely setose anterior margin; propodus large, broadened distally, densely setose along anterior and posterior margins, palmar margin irregularly toothed, postero-distal processes usually large; dactylus with numerous outer marginal setae.

Pereopods 3 and 4 unequal; segment 4 stout; dactylus well developed. Pereopods 5–7, bases deep, variously narrowed, hind lobes reduced, small; dactylus well developed.

Pleon plates 1 and 2, hind corners minutely acuminate; pleon plate 3, hind corner usually produced, acute. Pleopods elongate; peduncles strongly setose laterally. Uropod 1, peduncle with strong interramal spur. Uropod 3, outer ramous strong, terminal segment distinct. Telson lobes regular, weakly (or not) fused basally, marginal notches closely subapical.

Coxal gills 2–5 large, 6 often distinctly smallest. Brood plates sublinear, short.

Distribution. Marine waters of boreal and arctic parts of Northern hemisphere.

Remarks. Jarret and Bousfield established features of the dorsal armament as one of the main signs of the genus ( Jarret & Bousfield 1996: p. 36, fig. 1). Features of dorsal armament of Q. formosa and of Quasimelita tolyza sp. nov. and Quasimelita serraticoxae sp. nov. indicate that this feature is unstable and can not be used as a generic characteristic. The structure of the mouthparts of Q. tolyza sp. nov. also deviates from the typical for the genus Quasimelita : maxilla 1, inner plate densely setose; maxilla 2, inner plate with numerous submarginal facial setae. With the addition of the new species described here, the only stable features of the genus Quasimelita are signs of armament of pereopod 2: carpus large, with broadly setose posterior margin and densely setose anterior margin; propodus large, densely setose along anterior and posterior margins.