Eosymtes magnumoculis, Labay, 2022

Labay, Vjacheslav S., 2022, Review of amphipods of the family Pleustidae Buchholz, 1874 (Amphipoda) from the coastal waters of Sakhalin Island (Far East of Russia). II. Subfamily Eosymtinae Bousfield & Hendrycks, 1994, Zootaxa 5125 (5), pp. 547-562 : 551-557

Eosymtes magnumoculis sp. nov.

Figures 1b , 2b, e, h, k, n , 3c, d, e , 4–9

Diagnosis. Eyes large, reniform. Body smooth; urosome segment 2 not occluded dorsally.

Antenna 1, segments of peduncle without anterodistal process; flagellum with 27+ articles. Lower lip, outer lobes rounded not widely spread. Mandible, lacinia mobilis with 1–2 outer lateral processes. Maxilla 2, outer and inner plates densely setose. Maxilliped, inner plate reaching the 1/3 or 1/2 of palp segment 1; outer plate reaching about 0.5 x length of palp segment 2; palp segment 2 the longest, inner margin densely setose. Coxal plate 1–3 medium; coxal plate 4 much broader, deeply excavated posteroproximally; coxal plates 5–7 posterolobate, posteriorly rounded. Gnathopod 1, merus without acute tooth posterodistally, palmar margin without medial tooth, with 3 clusters of posterodistal strong setae (spines). Gnathopod 2, carpal lobe medium in length, merus with acute tooth posterodistally, palmar margin without medial tooth, with 2 clusters of posterodistal strong setae (spines). Pereopods 5–7, dactylus long, 0.5–0.51 times as long as propodus. Epimeral plate 3, posteroventral corner without a large process. Uropods 1–3, peduncle and ramie with numerous marginal small robust setae.

Male: unknown.

Type material. Holotype, female, 8.9 mm, Х 54400 /Cr-2428, Sea of Okhotsk , Far East of Russia (52º15493′ N 143º81916 E, 56 m), sands with silt, V. A. Alaskerov, 28 June 2019 . Paratype: 1 female, 6.5 mm, Х 54401 /Cr- 2429, with same data as holotype .

Additional material. Paratypes: 3 females, Х 54402 /Cr- 2430, Sea of Okhotsk , Far East of Russia (52º23,820 N 144º37,308 E, 160 m), sands with silt, M.G. Rogotnev, 26 July 2019 ; 5 females, Х 54403 /Cr- 2431, Sea of Okhotsk, Far East of Russia (52º13,7879 N 143º81,9639 E, 45 m), sands, M.G. Rogotnev, 27 July 2019 ; 15 females, Х 54404 /Cr- 2432, Sea of Okhotsk , Far East of Russia (52º08,853 N 144º39,0695 E, 115 m), sands with silt, M.G. Rogotnev, 26 July 2019 ; 1 female (from the author’s collection), 5.2 mm, Sea of Okhotsk , Far East of Russia (50º00 N 144º155 E, 96 m), silt, I.N. Moukhametov, 22 June 2020 ; 1 female (from the author’s collection), 4.8 mm, Sea of Okhotsk , Far East of Russia (50º00 N 144º155 E, 96 m), silt, I.N. Moukhametov, 22 June 2020 ; 9 females (from the author’s collection), Sea of Okhotsk , Far East of Russia (50º00 N 144º155 E, 96 m), silt, I.N. Moukhametov, 22 June 2020 ; 1 female (from the author’s collection), 6.3 mm, Sea of Okhotsk , Far East of Russia (55º93,87 N 155º32,31 E, 54 m), sands, N. V. Shalaputin, 28 July 2020 .

Type locality. The eastern coast of Sakhalin Island , Sea of Okhotsk, Far East of Russia (52º15,493 N 143º81,916 E, 56 m) .

Description. Female (8.9 mm). Rose-coloured when alive; color in alcohol almost white-colourless. Body smooth ( Fig. 4a ). Microstructure of surface with wavy striation ( Fig. 8e ).

Head ( Fig. 4b ): slightly shorter than pereonites 1 & 2 combined; Rostrum short, about 1/8 times as long as peduncular segment 1 of antenna 1, apex acute; eyes large, subreniform, light-brown; anterior head lobe prominent, rounded, lower margin processed ahead by the acute tooth. Antenna 1 ( Fig. 4g, h ): medium length; flagellum bearing 27+ articles; peduncle article 1 is 2 times as long as article 2, with a few short simple setae at the distal corner of lower margin, segments 1 & 2 without large anterodistal process each, article 3 3/5 times the length of article 2; accessory flagellum scale-like. Antenna 2 ( Fig. 4i ): broken, peduncular articles 1, 2 together 1.7 times as article 3 length; article 1 with posterodistal protrusion, article 4 0.86 times as article 5, both with 3 tufts of simple setae at the lower margin each; flagellum segments with a crown of short setae around distal margin. Upper lip ( Fig. 4c ): apical lobes slightly asymmetric, without terminal setae. Mandible ( Figs. 4d, e, f, j, k, l, m , 5g ): incisor margins with 6 teeth, accessory spine rows with 6–7 slender blades; lacinia mobilis with 1–2 outer lateral processes; molar strong, columnar, with strongly ridged grinding surface and with a medial molar seta; palp 3-articulate, article 1 of palp with or without distal seta, segment 2 with an indefinite-quantity (8–20) of simple setae (D-2 setae), segment 3 subequal to segment 2, with posterior row of 11–12 specific plumose D3-setae and with a few long simple setae, with group of 3 long plumose distal E3-setae and one short simple E-3 seta. Lower lip ( Fig. 5f ): inner lobes small; outer lobes ovoid, setose. Maxilla 1 ( Fig. 5a ): inner plate short, with 2 plumose setae apically; outer plate elongate, apically with 2 rows of 9 strong setae (setae of anterior row bifurcate, setae of posterior row pectinate); palp 2-articulate, article 2 with rare thin simple setae at the outer surface and with a subapical row of 6–7 simple setae, apical margin of article 2 with 7–8 long stout spine-like setae. Maxilla 2 ( Fig. 5b ): inner plate with 2 strong plumose setae on the inner margin. Maxilliped ( Fig. 5c ): inner plate middle length, reaching the 1/3 or 1/2 of palp segment 1, with 3–4 short annulate and conate setae, without setules (Watling type II.A4) ( Watling 1989) at the truncated apex; outer plate reaching about 0.5 x length of palp segment 2, rounded outer-apically and with rectangular inner corner, inner margin with submarginal row of simple setae, apex with 3 strong setae; palp 4-articulate, the percentage of total length of the articles of the palp 20.0% (article 1), 31.4% (article 2), 26.9% (article 3) and 21.7% (article 4); article 3 with specific setae, which plumose in the middle part; article 4 (dactylus) slender, slightly curved.

Pereon: Gnathopod 1 ( Fig. 5d, e , 9a, b, f, g ): coxa short, slightly pulled forward, with one small posterodistal cusp, inner side with oblique belt of short robust setae; basis slightly concave anteriorly and convex posteriorly, with anterior submarginal row of simple setae at the inner surface, more long in the distal part; merus with 2 tufts of simple setae and with a short row of long simple setae along the posterior margin; carpus 0.71 times as long as propodus, posterior lobe short, shallow, with 3 tufts of simple setae along posterior margin and with posterodistal row of numerous specific setae, which plumose in the middle part, crossing over at the distal margin; propodus 1.8 times as long as wide, palmar margin oblique, roundly passing to the posterior margin, 1.37 times as long as posterior margin, without medial tooth, with 3 clusters of posterodistal robust setae; dactylus shorter than palmar margin of propodus, slightly curved. Gnathopod 2 ( Fig. 6a, b , 9c, d, e ): coxa short, subquadrate, with one small posterodistal cusp; basis long, slightly concave anteriorly and convex posteriorly, with dense rows of short simple setae along anterior and posterior margins; merus with two groups of simple setae along posterior margin, distal margin truncated, with a few simple setae and with an acute tooth at the posterior angle; carpus medium, 0.68 times as long as propodus, posterior lobe shallow, with 3 tufts of setae along posterior margin and with a crown of long setae at the distal margin of lobe; propodus expanded distally with oblique palmar margin, 1.8 as long as wide, with 3 groups of simple setae at the posterior margin, palmar margin 0.89 times as long as posterior margin, without medial tooth, with 2 clusters of posterodistal strong setae (spines); dactylus slightly shorter than palmar margin, slightly curved. Pereopod 3 ( Fig. 6c ): coxa rectangular, 1.8 times as long as wide, with one small posterodistal cusp; leg slender; basis sublinear, slightly concave anteriorly and convex posteriorly, with dense row of short simple setae along anterior margin and with few groups of setae at the posterior margin; merus 1.14 times as long as carpus, produced forwards along anterior margin of carpus; propodus long, 1.36 times as long as carpus; dactylus long, 0.51 times as long as propodus. Pereopod 4 ( Fig. 6d ): coxa 1.28 times as long as wide, with deep excavation in the proximal ¼ of posterior margin; basis to dactylus as for pereopod 3. Pereopod 5 ( Fig. 7a ): coxa antero- and posterolobate, with rounded ventral front margin, posterior lobe pulled back and down, rounded distally; basis with posterior lobe, width 0.75 times as length, slightly expanded distally, posterior margin slightly convex, crenulated; merus produced forwards along posterior margin of carpus; carpus more narrow and 0.6 times as long as merus; propodus linear, 1.7 times as long as carpus; dactylus long, 0.53 times as long as propodus, weakly curved, slender. Pereopod 6 ( Figs. 7b ): coxa posterolobate, with truncated front margin, posterior lobe deep, pulled back and down, rounded distally; basis suboval, broadened, with distinct posterior lobe, posterodistal corner rounded, width 0.81 times length, posterior margin convex, crenulated; merus produced distally along posterior margin of carpus, narrow; carpus 0.67 times as long as merus; propodus sublinear, 1.49 times as long as carpus; dactylus long, 0.54 times as long as propodus, weakly curved, slender. Pereopod 7 ( Fig. 7c ): coxa half-rounded; basis broadened, with distinct posterior lobe, posterodistal corner rounded, width 0.79 times length, posterior margin convex, crenulated; ischium; merus, carpus, propodus and dactylus as in pereopod 6. Coxal gills on pereopods 2–6. Coxal gill 6 smaller than gill 5.

Pleon: Epimeral plates: ( Fig. 7d, e, f ) plates 1–3, posterior corners with small tooth each; plate 1 rounded triangular, without setae; plate 2, ventral margin convex, with 3–4 thin spine-like setae; plate 3, posterior margin rounded, ventral margin straight with 3 spine-like setae in anterior half. Pleopods: ( Fig. 7g, h, i, j, k ) normal; inner ramus slightly shorter than outer ramus, coupling basis of inner ramus with 4–6 specific stout two-pointed plumose setae along inner margin (6 setae on pleopod 1, 5 setae on pleopod 2 and 4 setae on pleopod 3). Uropod 1: ( Fig. 8a ) peduncle 1.2 times as long as outer ramus, with numerous marginal small spine-like setae and with large spinelike setae at the outer-distal corner; outer ramus 0.92 times as long as inner ramus. Uropod 2: ( Fig. 8b ) inner ramus 1.26 times longer than peduncle; outer ramus 0.76 times as long as inner; peduncle and both rami with numerous marginal small spine-like setae. Uropod 3: ( Fig. 8c ) inner ramus 2.1 times longer than peduncle, with acute and non-spinose apex; outer ramus about 0.71 times as long as inner; outer ramus with a row of 6 small spine-shaped setae along lateral and medial margins each, with acute and non-spinose apex. Telson: ( Fig. 8d ), width 0.65 times length, linguiform, apically rounded, with 2 subapical notches, length about 1.6 x width, with proximal ventral keel, plumose marginal penicillate setae are absent.

Male: unknown.

Etymology. Species name magnumoculis is based on the Latin “magnum oculis” (large-eyed), reflecting the size of the eyes. The name is masculine.

Ecology: Eosymtes magnumoculis was found in the depth interval of 45–160 m on the sands and silt bottom in the layer of constant low temperature (-1.2 – +0.5°C). Females with developed marsupium were encountered in June and July. The species is found on the shelf of north-eastern Sakhalin Island and on the shelf of western Kamchatka Peninsula.

Distribution: The Sea of Okhotsk; on the shelf of north-eastern Sakhalin Island and western Kamchatka Peninsula ( Fig. 11 ).

Remarks. Eosymtes magnumoculis sp. nov. is morphologically similar to the species E. minutus ( Bousfield and Hendrycks 1994; Hendrycks and Bousfield 2004). E. magnumoculis differs from E. minutus by the following combination of character states ( Figs. 1–3 ): big eyes; maxilla 2, outer and inner plates densely setose; maxilliped, palp segment 2, inner margin densely setose; uropods 1–3, peduncle and rami with numerous marginal short spinelike setae.

Figures

FIGURE 1. Eosymtinae Bousfield & Hendrycks, 1994, lateral view: a—Eosymtes minutus Bousfield and Hendrycks, 1994 (from Bousfield and Hendrycks 1994: fig. 7), b—Eosymtes magnumoculis sp. nov., c—Cognateosymtes serraticoxae Labay, 2018 (from Labay 2018: fig. 2a)

FIGURE 2. Eosymtinae Bousfield & Hendrycks, 1994: a–c—peduncle of antenna 1; d–f—maxilla 2; g–i—palp of maxilliped; j–l—coxal plates 1–3 posteroventrally; m, n, o—propodus and dactylus of pereopods 3–7; a, d, g, j, m—Eosymtes minutus Bousfield and Hendrycks, 1994 (from Bousfield and Hendrycks 1994), b, e, h, k, n—Eosymtes magnumoculis sp. nov., c, f, i, l, o—Cognateosymtes serraticoxae Labay, 2018 (from Labay 2018)

FIGURE 3. Eosymtinae Bousfield & Hendrycks, 1994: a—urosome segments 1–3; c, f—uropod 1; d, g—uropod 2; b, e, h—uropod 3; a, b—Eosymtes minutus Bousfield and Hendrycks, 1994 (modified from Bousfield and Hendrycks 1994), c, d, e—Eosymtes magnumoculis sp. nov., f, g, h—Cognateosymtes serraticoxae Labay, 2018 (from Labay 2018)

FIGURE 4. Eosymtes magnumoculis sp. nov., holotype, female, 8.9 mm (the shelf of eastern Sakhalin): a—lateral view, b—cephalon, c—upper lip, d—left mandible, e—incisor and molar of left mandible, f—incisor and molar of right mandible; paratype, female, 6.5 mm (the shelf of eastern Sakhalin): g—antenna 1, h—additional flagellum of antenna 1, i—antenna 2, j—incisor and molar of right mandible, k—lacinia mobilis of right mandible; paratype, female, 5.3 mm (the shelf of eastern Sakhalin): l—lacinia mobilis of right mandible; paratype, female, 6.3 mm (the shelf of western Kamchatka): m—lacinia mobilis of right mandible: scales: a, g, i—1 mm; b—0.5 mm; c, d—0.2 mm, e, f, h, j, k, l, m—0.1 mm

FIGURE 5. Eosymtes magnumoculis sp. nov., holotype, female: a—maxilla 1, b—maxilla 2, c—maxilliped, d—gnathopod 1, e—palm of propodus and dactylus of gnathopod 1; paratype, female, 5.3 mm: f—lower lips; paratype, female, 6.3 mm: g—incisor and molar of right mandible; scales: d—0.5 mm; c—0.2 mm; a, b, e, f—0.1 mm

FIGURE 6. Eosymtes magnumoculis sp. nov., holotype, female: a—gnathopod 2, b—palm of propodus and dactylus of gnathopod 2, c—pereopod 3; d—pereopod 4; scales: a, c, d—1 mm, b—0.1 mm

FIGURE 7. Eosymtes magnumoculis sp. nov., holotype, female: a—pereopod 5, b—pereopod 6, c—pereopod 7, d, e, f—epimeral plates 1–3, g—pleopod 2, h—coupling spines of pleopod 3, i, j, k—coupling setae of pleopods 1, 2 and 3; scales: a–g—1 mm, h–k—0.1 mm

FIGURE 8. Eosymtes magnumoculis sp. nov., holotype, female: a—uropod 1, b—uropod 2, c—uropod 3, d—telson; paratype, female, 6.3 mm (the shelf of western Kamchatka): e—microstructure of surface; scales: a, b, c—1 mm, d—0.2 mm, e—0.01 mm

FIGURE 9. Eosymtes magnumoculis sp. nov., paratype, female, 4.8 mm (the shelf of eastern Sakhalin): a—gnathopod 1, b— palm of propodus and dactylus of gnathopod 1, c—gnathopod 2, d—palm of propodus and dactylus of gnathopod 1; paratype, female, 5.2 mm (the shelf of eastern Sakhalin): e—coxal plate 2 with coxal gill and brood plate; paratype, female, 6.3 mm (the shelf of western Kamchatka): f, g—inner side of coxal plate 1; scales: a, c, e—0.5 mm, b, d, f—0.1 mm; g—0.02 mm

FIGURE 11. Distribution of Eosymtinae species in Far Eastern Region