Gurjanovometopa onenusica, Labay, 2025

Gurjanovometopa onenusica sp. nov.

Figures 1–6 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6

Type material. Holotype, female, 2.4 mm, Mb-1269 (Zoological Museum of MSU), the Sea of Japan, Strait of Tartary, shelf of the south-western Sakhalin Island (46°13'208 N 141°53'353 E, 15 m), coarse sand with grit, 14 October 2023, V. S. Labay . Paratype: 1 male, 2.9 mm, Mb-1270 (Zoological Museum of MSU), with same data as holotype . Paratypes: 7 females, X 54727 / 2486 ( Zoological Museum of Far East Federal University ), the Sea of Japan, Strait of Tartary, shelf of the south-western Sakhalin Island (46°07'317 N 141°54'581 E, 15 m), a crevice between rocks filled with grit, 17 May 2024, V. S. Labay . 9 males, X 54728 / 2487 ( Zoological Museum of Far East Federal University ), with same data as previous .

Type locality. The south-western coast of Sakhalin Island, Strait of Tartary, Sea of Japan, Far East of Russia (46°13'208 N 141°53'353 E, 15 m).

Etymology. The species name onenusica derived from the river Onenusi near the type locality.

Diagnosis. Antenna 1 of male, articles of flagellum with aesthetascs. Mandibular palp with 2 apical setae only. Maxilliped, inner plate apically with single short robust seta (spine) and one simple seta. Gnathopod 1 small, simple, merus and carpus with long posterior lobe each, propodus elongate, almond-shaped, posterior margin of dactylus with 1–2 setae. Gnathopod 2 large, with slightly oblique palmar margin, anterior margin of basis of pereopods 3–4 with 1–2 short setae distally. Telson long, linguiform.

Description. Holotype, female (2.4 mm; Mb-1269). Body is colorless in alcohol. Pereonites, Pleonites, and Urosomites smooth. Coxal plate 1 small, indistinct; coxal plates 2 and 3 large, the third it is 1.5 times wider than previous one; coxal plate 4 extremely large; coxal plates 5–7 small.

Head. Rostrum small. Ocular lobes rounded triangular. Eyes colorless in alcohol, round, medium. Antenna 1 short, ca. 0.3 times of body length; peduncular articles 1–3 with length ratio of 1.00:0.63:0.55, article 1 stout, with 2 plumose setae near antero-distal corner; accessory flagellum absent; flagellum with 5 articles. Antenna 2 slightly longer than antenna 1, slender; peduncular articles 3–5 with length ratio of 1.0:1.5:1.5, articles 2 and 3 with few setae at the antero-distal and postero-distal angles each; flagellum with 4 articles, terminal article bearing a crown of setae distally. Labrum, apical lobes slightly asymmetric. Mandibles, incisors wide, with 7–8 distal denticles; laciniae mobilis broad, left one fan-shaped, with 10 denticles, right one rectangular, with 10 denticles; accessory blades 6 in left, 7 in right; palp l-articulate, relatively short, slender, with 2 apical “E” setae. Lower lips, inner lobes weak, rounded; outer lobes triangular-rounded at distal margin. Maxilla 1 with small inner plate bearing single seta; outer plate with 6 large robust setae and one thin seta apically, medial margin bearing several feeble setae; palp l-articulate, tip of palp acutely projected, with 3 robust setae, with a subapical row of 2 setae. Maxilla 2, inner plate with 4 apical setae; outer plate longer, truncated, with 5 setae on the tip. Maxilliped; distal margins of inner plates each bearing one robust spine-like seta and one short seta; distomedial lobe of outer plate short, tip with 3 short setae, lateral margin with one short seta; palp, length ratio of articles 1–4 being as 1.0:0.7:1.1:1.3, articles 1 and 2 wide, medial margins with 3–4 robust setae, article 3 with a group of 4 robust setae on distomedial corner and with sublateral row of thin setulae on the inner surface, article 4 slightly curved, medial margin bearing a row of numerous feeble setae.

Pereon. Gnathopod 1 small; basis stubby, anterior margin smooth, posterodistal corner with 2 short setae; merus with the long postero-distal lobe bearing 6 robust setae on the tip and with a row of short thin setae posteriorly, inner surface with a field of short setulae; carpus short, with the long postero-distal lobe bearing 2 specific robust comb setae and one specific trifurcate seta, distal margin with a row of 4 long setae along inner surface; propodus long, simple, almond-shaped, narrowed distally, without palm, with single seta in the distal half of anterior margin, with 2 long and 2 short setae along posterior margin, inner surface with a short row of numerous feeble setae; dactylus slightly curved inside, with one seta at the posterior margin. Gnathopod 2 subchelate, stout; basis straight, anterior margin lined with 2 evenly-spaced rare short setae, posterodistal corner with short seta; merus rectangular posterodistally, posterior margin smooth, posterodistally with 2–3 short setae; carpus with posterior lobe bearing 2 specific robust comb setae on the tip and with a row of feeble setulae on the inner surface along distal margin; propodus stout, slightly dilated distally, ca. 3 times length of carpus, palm slightly oblique, with a powerful tooth at the postero-distal corner bearing robust spine-like seta subapically, with a rare row of short setae along palmar margin and with robust spine-like seta at the base of postero-distal tooth, inner surface with a pair of robust spine-like setae postero-distally; dactylus curved posteriorly. Pereopod 3 slender; basis, anterior and posterior margins with few short setae along distal 1/3; propodus ca. 1.2 times as long as carpus, posterior margin with 3 short setae along the distal half; dactylus narrow, 0.4 times as long as propodus, posterior margin is smooth. Pereopod 4 slender, similar to pereopod 3; propodus with 4 rare short setae along posterior margin. Pereopod 5 longer than pereopod 4; basis straight, anterior margin lined with 2 tiny setae; merus with short posterodistal process bearing one long seta at the tip, merus and carpus, anterior margin each with one short robust seta and 2 setae at the antero-distal corner each; propodus thin, anterior margin with 1–2 short robust setae; dactylus narrow, 0.5 times as long as propodus, posterior margin is smooth. Pereopods 6 and 7 similar to pereopod 5.

Pleon. Epimeral plates 1–3, posterodistal corners produced; ventral margin of epimeral plate 1 with 2 short setae, ventral margins of plates 2 and 3 with one short seta each. Pleopods slender, pleopod 3 the shortest; peduncles with paired retinacula (coupling spines) on inner distal margin; inner ramus shorter than outer ramus; inner ramus of pleopods with 4–5 articles, outer ramus of pleopods 1 and 2 with 6 articles, outer ramus of pleopod 3 with 4 articles. Uropod 1 long; peduncle without dorsolateral robust setae; rami short, 0.35 times as long as peduncle, outer ramus slightly longer than inner ramus, smooth, inner ramus with single dorsal robust seta. Uropod 2 ca. 0.6 times as long as uropod 1, peduncle and rami without dorsolateral robust setae; rami 0.7 times as long as peduncle, outer ramus slightly longer than inner ramus. Uropod 3 ca. 0.65 times as long as uropod 2, peduncle smooth; single ramus 2- articulate, article 1 with single seta at the base of article 2, article 2 subequal to article 1 in length, tip acute. Telson ca. 2.4 times longer than broad, smooth.

Paratype, male (2.9 mm; Mb-1270) (fig. 6). Similar to female. Males differ from females in the structure of antenna 1 and antenna 2, in the armament of the carpus of gnathopod 1, in the structure of the propodus of gnathopod 2, and in the structure of the pleopods. Morphological differences between male and female shown in the table 1. Sexual dimorphism is distinctly marked in the structure of gnathopod 2. In male propodus of gnathopod 2 smaller than in female, 0.64 times as long as basis, expanded distally, the tooth at the postero-distal corner wide (width equals to length) with crenulated posterior margin. In female propodus of gnathopod 2 large, 0.92 times as long as basis, not expanded distally, the tooth at the postero-distal corner narrow (length exceeds the width), posterior margin of tooth not crenulated.

Variations. In the armaments of postero-distal lobe of carpus of gnathopod 1 in males and females (2 specific robust comb setae and one specific trifurcate seta or 3 specific robust comb setae or 2 specific robust comb setae only).

Ecology: Gurjanovometopa onenusica found in the depth range of 10–15 m on the coarse sand with grit among rocks. The water temperature in the habitat of the species varied from 2.6 to 5.3ºC in May and June inclusive and from 4.5 to 14.3ºC in July—October.

Distribution. The coastal shallow waters of the Strait of Tartary (Sea of Japan) off southwestern Sakhalin Island in the zone of the cold water (cold spot of Makarov), which is caused by the influx of a tidal wave spreading from the Sea of Okhotsk onto the Rock “Stone of danger” in the Laperouse Strait [ Shevchenko et al., 2005; Mitnik et al., 2006].