Cognateosymtes, Labay, 2018

Labay, Vjacheslav S., 2018, Cognateosymtes serraticoxae, new genus, new species, a pleustid amphipod from the Sea of Japan (Crustacea: Amphipoda: Gammaridea: Pleustidae: Eosymtinae), Zootaxa 4521 (2), pp. 220-230 : 221

Genus Cognateosymtes n. gen.

Figures 2–8 .

Type species. Cognateosymtes serraticoxae sp. nov.

Species. Cognateosymtes serraticoxae sp. nov. from the shelf of western Sakhalin Island (Sea of Japan).

Diagnosis. Body medium, smooth. Urosome segment 2 not occluded dorsally. Rostrum short. Anterior head lobe truncated. Eyes large, subreniform. Antenna 1, anterodistal peduncular process strong.

Upper lip, apical lobes slightly asymmetric. Lower lip regular, inner lobes weak, narrowly sloped. Mandible, spine-row short, with 6 pectinate blades; left lacinia 6 dentate, right lacinia blade-like. Maxilla 2, inner plate with 2 strong submarginal and subapical setae. Maxilliped, outer plate high, with one strong apical seta only and straight inner cutting edge; inner plate with 3 small inner spiniform setae and with 3 rows of 2–4 short stout plumose setae; palp segment 3 not produced distally, dactyl slender, slightly curved, not pectinated.

Coxal plates 1–4 medium, little deeper than pereon, increasing posteriorly; hind corners of coxae 1–2 each with 3–5 small cusps. Pereopods 1 & 2 (gnathopods 1 & 2) medium, similar in form, carpus longer than ¾ length of propodus, palmar margin short, oblique, smoothly continuous with densely setose, elongate posterior margin.

Pereopods 3 and 4 slender, medium long, dactylus medium in length. Pereopods 5–7 unequal in form; pereopod 5 the shortest; basis broadened, rounded behind, hind margin weakly serrate.

Pleon plates 1–3, hind corners acuminate, not produced, posterior margins slightly sinuous. Uropod 3 slender, outer ramus not more than 2/3 the length of the inner ramus.

Telson linguiform, apex subtruncate, paired notch and setae prominent; telson keeled proximally.

Marsupial plates are leaf-like, broad, with short setae ( Fig. 8b ).

Male is unknown.

Distribution. The shelf of western Sakhalin Island, Sea of Japan.

Relationships: Cognateosymtes n. gen. is similar to the genus Eosymtes Bousfield & Hendrycks, 1994 by details of morphology of mandible molar, by the presence of blade-like right lacinia, inner plate of maxilla 2 with 2 strong submarginal and subapical setae; by the form of gnathopod—propodal palmar margins lacking submedial tooth. Cognateosymtes differs from Eosymtes by the following combination of character states ( Fig. 8 ): antenna 1, peduncular segment 1 with strong anterodistal processes; coxae 1–3, posterodistal cusps multiple; outer and inner plates of maxilla 2 with numerous apical setae; maxilliped, palp segment 2 linear, inner margin densely setose; dactylus of pereopods 3–7 medium in length.

Etymology: The genus Cognateosymtes is based on the Latin word “cognata” (agnate) combined with the genus name Eosymtes. The name is masculain in gender.

Figures

FIGURE 2. Cognateosymtes serraticoxae sp. nov., holotype, female: a—lateral view, b—cephalon, c—antenna 1, dpeduncle articles 1–3 of antenna 2, e—upper lip, f—left mandible; scale: a, b, c, d, f—1 mm; e—0.1 mm.

FIGURE 3. Cognateosymtes serraticoxae sp. nov., holotype, female: a—molar of the left mandible, b—incisor of the left mandible, c—incisor of the lright mandible, d—lower lips, e—left maxilla 1, f—palp of the right maxilla 1; scale: 0.1 mm.

FIGURE 4. Cognateosymtes serraticoxae sp. nov., holotype, female: a—maxilla 2, b—maxilliped, c—pereopod 1, d—palm of pereopod 1, inner side, e—pereopod 2, f—palm of pereopod 2, inner side; scale: a, d, f—0.1 mm, b, c, e—1 mm.

FIGURE 5. Cognateosymtes serraticoxae sp. nov., holotype, female: a—pereopod 3, b—pereopod 4, c—pereopod 5, dpereopod 6; scale: 1 mm.

FIGURE 6. Cognateosymtes serraticoxae sp. nov., holotype, female: a—pereopod 7, b, c, d—epimer 1–3, e—pleopod 3, fcoupling spines of pleopod 3, g, h, i—coupling setae of pleopod 1, 2, 3; scale: a–e—1 mm, f–i—0.1 mm.

FIGURE 7. Cognateosymtes serraticoxae sp. nov., holotype, female: a—uropod 1, b—uropod 2, c—uropod 3, d—telson; scale: a–c—1 mm, d—0.1 mm.

FIGURE 8. Cognateosymtes serraticoxae sp. nov., paratype, female: a—pereopod 1, b—pereopod 2; scale: 1 mm.