Cognateosymtes serraticoxae, new genus, new species, a pleustid amphipod from the Sea of Japan (Crustacea: Amphipoda: Gammaridea: Pleustidae: Eosymtinae) Author Labay, Vjacheslav S. text Zootaxa 2018 2018-11-14 4521 2 220 230 journal article 27962 10.11646/zootaxa.4521.2.4 afbbeeff-25e4-44c5-b563-5c741fa8d0f9 1175-5326 2609817 FB9A3022-7029-421B-98F0-78E4CB3ADAEE Cognateosymtes serraticoxae sp. nov. Figures 1–8 Diagnosis . With the characters of the genus. Eyes large, subreniform. Body medium, smooth; urosome segment 2 not occluded dorsally. Rostrum short, about 1/6 times as long as peduncular segment 1 of antenna 1, apex acute. Antenna 1, segment 2 of peduncle with small anterodistal process, accessory flagellum minute, scale-like; flagellum with 34 articles, length about 3.5 x peduncle. Lower lip, outer lobes rounded not widely spread. Mandible, incisor margins with 6–7 teeth, accessory spine rows with 6 slender blades; molar with strongly ridged grinding surface and with a medial molar seta; palp segment 3 slightly shorter than segment 2, segment 2, inner margin setose; segment 1 without setae. Maxilla 1, inner plate with 2 plumose apical setae; outer plate with 9 strong pectinate setae (spine-like setae). Maxilliped, inner plate reaching the middle of palp segment 1; outer plate reaching about 0.5 x length of palp segment 2; palp segment 2 the longest; segment 3 narrower, slightly broadened medially; dactylus slender, slightly curved and shorter than palp segment 3. Coxal plate 1–3 medium; coxa plate 4 much broader, deeply excavated posteroproximally; coxal plates 5–7 posterolobate, posteriorly rounded. Pereopod 1, merus with acute tooth posterodistally, palmar margin without medial tooth, with 2 clusters of posterodistal strong setae (spines). Pereopod 2 slightly widened; carpal lobe short, merus without acute tooth posterodistally. Pereopods 5–7, dactylus medium in length, 0.44–0.5 times as long as propodus. Epimeral plate 3, posteroventral corner without a large process. Male: unknown. 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. Type material . Holotype female, 6 mm , Х 50437 /Cr-2276, Tatar Strait. Sea of Japan , Far East of Russia ( 49°29.5'N 142°06.3'E , 17 m ), rocks, M.G. Rogotnev , 13 July 2017 . Paratypes : 1 female , 6 mm , Х 50438 /Cr-2277, with same data as holotype ; 1 female , 6 mm , Х 50439 /Cr-2278, with same data as holotype . Type locality . The western coast of Sakhalin Island , Tatar Strait. Sea of Japan , Far East of Russia ( 49°29.5'N 142°06.3'E , 17 m ) . Description . Female ( 6 mm ). Vital body color is unknown; color in alcohol almost colourless, uniformly pale yellow. Body medium, smooth ( Fig. 2a ). Head ( Fig. 2b ): slightly shorter than pereonites 1 & 2 combined, rostrum about 1/5 times as long as peduncular segment 1 of antenna 1; eyes large, subreniform; anterior head lobe prominent, truncated, lower margin processed ahead by the acute tooth. Antenna 1 ( Fig. 2c ): medium length, nearly 40% of body length; flagellum bearing 34 articles; peduncle article 1 is 2 times as long as the length of article 2, with a few simple setae at the distal corner of posterior margin, segments 1 & 2 with large anterodistal process each, article 3 0.38 times the length of article 2; accessory flagellum, scale-like. Antenna 2 ( Fig. 2d ): destructed, articles 1, 2 together slightly shorte than article 3; article 1 with long anterodistal protrusion. Labrum ( Fig. 2e ): apical lobes slightly asymmetric, setose. Mandible ( Figs. 2f , 3a, b, c ): molar strong, columnar, with pavement-type grinding surface and with a medial molar plumose seta; palp 3-articulate, article 1 of palp without setae, palp segment 2 with a row of 12 simple setae (D-2 setae), palp segment 3 with posterior row of 15–16 specific plumose D3-setae (proximal setae are needle-like with forked tip, middle setae are plumose with forked tip and distal setae are comb-like), with group of 3 long simple distal E3- setae and one short simple E-3 seta. Labium ( Fig. 3d ): inner lobes small; outer lobes rounded, setose. Maxilla 1 ( Fig. 3e ): inner plate long, slightly narrowed distally, with 2 plumose setae apically; outer plate elongate, apically with 2 rows of 9 strong setae (external setae bifurcate, middle and internal setae pectinate); palp 2-articulate, article 2 with a distal row of thin simple setae at the outer margin and with a subapical row of 9 simple setae, apical margin of article 2 of left maxilla 1 with 8 long stout spine-like setae, apical margin of article 2 of right maxilla 1 with 8 short teeth-like setae. Maxilla 2 ( Fig. 4a ): inner plate with 2 strong plumose setae on the inner margin. Maxilliped ( Fig. 4b ): inner plates middle length, fully cleft, with 3 short conate setae (Watling type II.A4) ( Watling 1989 ) at the truncated apex; outer plate elongated, rounded apically, inner margin with submarginal row of simple setae, apex with one strong seta only; palp 4-articulate, the percentage of total length of the articles of the palp 25% (article 1), 31% (article 2), 24% (article 3) and 20% (article 4); article 4 (dactylus) slender, slightly curved. Pereon : Pereopod 1 (gnathopod 1) ( Fig. 4c, d ): coxa short, slightly pulled forward and down, with 4 small posterodistal cusps; basis slightly convex posteriorly, with dense anterior submarginal row of simple setae at the inner surface; merus with a tuft of 2 simple setae at the border of 1/2 of posterior margin, distal margin with a row of long simple setae; carpus 0.86 times as long as propodus, posterior lobe shallow, with a tuft of 2 simple setae at the border of 1/6 of posterior margin, with posterodistal row of numerous simple setae passing to the distal margin; propodus suboval, 2 times as long as wide, palmar margin smoothly oblique, roundly passing to the posterior margin, 0.64 times as long as posterior margin, without medial tooth, with 3 clusters of posterodistal robust setae; dactylus as long as palmar margin of propodus, curved. Pereopod 2 (gnathopod 2) ( Fig. 4e, f ): coxa deep, with 3 posterodistal cusps; basis linear, with a row of rare short simple setae anteriorly; merus with a few simple setae at the border of 1/2 of posterior margin, distal margin truncated, with a few simple setae and with a acute tooth at the posterior angle; carpus medium, 0.83 times as long as propodus, posterior lobe shallow, with 4 tufts of setae along posterior margin; propodus suboval, 1.93 as long as wide, with 4 groups of simple setae at the posterior margin, palmar margin smoothly oblique, 0.8 times as long as posterior margin, without medial tooth, with 2 clusters of posterodistal strong setae (spines); dactylus slightly shorter than palmar margin. Pereopod 3 ( Fig. 5a ): coxa deep, 1.7 times as long as wide, rounded anterodistally, with posterior tooth and with 2 small posterodistal cusps; leg slender; basis linear; merus as long as carpus, produced slightly forwards along anterior margin of carpus; propodus long, 1.28 times as long as carpus; dactylus short, 0.5 times as long as propodus. Pereopod 4 ( Fig. 5b ): coxa 1.26 times as long as wide, narrowed and rounded distally, with deep excavation posteromarginally; basis to dactylus as for pereopod 3. Pereopod 5 ( Fig. 5c ): coxa antero- and posterolobate, with rounded ventral front margin, posterior lobe rounded; basis with posterior lobe, width 0.69 times as length, posterior margin slightly convex, crenulated; merus slightly produced forwards along posterior margin of carpus; carpus more narrow and 0.8 times as long as merus; propodus linear, 1.4 times as long as carpus; dactylus short, 0.44 times as long as propodus, weakly curved, slender. Pereopod 6 ( Figs. 5d ): coxa posterolobate, with rounded front margin, posterior lobe subovate, pulled back and down; basis suboval, broadened, with distinct posterior lobe, posterodistal corner rounded, width 0.73–0.75 times as length, posterior margin convex, crenulated; merus produced distally along posterior margin of carpus, narrow; carpus 0.8 times as long as merus; propodus linear, 1.5 times as long as carpus; dactylus short, 0.5 times as long as propodus, weakly curved, slender. Pereopod 7 ( Fig. 6a ): coxa posterolobate, anterior margin rounded, posterior lobe subquadrate, rounded posteroventrally; basis broadened, with distinct posterior lobe, posterodistal corner rounded, width 0.77–0.78 times as length, posterior margin convex, crenulated; ischium; merus, carpus, propodus and dactylus as in pereopod 6. Coxal gills 2–6. Coxal gill 6 is smaller than gill 5. Pleon : Epimeral plates: ( Fig. 6b, c, d ) plates 1–3, posterior corners with small tooth each; plate 1 rounded triangular, with 2–3 short spine-like setae along ventral margin; plate 2, ventral margin slightly convex, with 3 spine-like setae; plate 3, posterior margin rounded, ventral margin straight with 3 spine-like setae. Pleopods: ( Fig. 6e, f, g, h, i ) normal; inner ramus slightly shorter than outer ramus, coupling basis of inner ramus with 3–5 specific stout two-pointed plumose setae along inner margin (5 setae on pleopod 1, 4 setae on pleopod 2 and 3 setae on pleopod 3). Uropod 1: ( Fig. 7a ) peduncle 1.2 times as long as outer ramus; outer ramus 0.89 times as long as inner ramus. Uropod 2: ( Fig. 7b ) inner ramus 1.4 times longer than peduncle, outer ramus 0.66 times as long as inner. Uropod 3: ( Fig. 7c ) inner ramus 2.6 times longer than peduncle, with acute and non-spinose apex; outer ramus about 0.59 times as long as inner; outer ramus with a row of 4–6 small spine-shaped setae along lateral and medial margins each, with acute and non-spinose apex. Telson: ( Fig. 7d ) medium in length, linguiform, apically rounded, length about 1.4 x width, with proximal ventral keel, plumose marginal penicillate setae are absent. Male: unknown. Variations: Coxa 1 with 4–5 small posterodistal cusps ( Fig. 8a ), coxa 2 with 3–4 small posterodistal cusps. Etymology . Species name serraticoxae based on a Latin words “ serratis ” (serrated) and “coxa”, that is caused by shape of coxal plates: with a ventral margin serrated posteriorly. The name is masculine in gender. 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. Ecology . C. serraticoxae was found in the depth 17 m on rock bottoms. Females with developed oostegites were detected in the type locality in July. Distribution . The northern part of the Sea of Japan , Tatar Strait, the shelf of south-western Sakhalin Island ( Fig. 1 ).