Dactylopleustes ornatus, Labay, 2025

Labay, Vjacheslav S., 2025, Review of amphipods of the family Pleustidae Buchholz, 1874 (Amphipoda) from the coastal waters of Sakhalin Island and Kamchatka Peninsula (Far East of Russia). IV. Subfamily Dactylopleustinae Bousfield and Hendrycks, 1994, Zootaxa 5627 (2), pp. 201-253 : 234-242

Dactylopleustes ornatus sp. nov.

Figures 1h , 2i, r , 3i, r , 4g, p , 5g, p , 6k, l , 7l, m , 8e, l , 24–30 , 36

Type material. Holotype: female, 3.1 mm, Х 54601 /Cr-2459, Sea of Okhotsk, Sakhalin, Aniva Bay (46°36'35"N 142°59'57"E, littoral), rock, on Strongylocentrotus intermedius , 28 July 2021, collector S.V. Labay . Paratypes: 1 female, 2.9 mm, Х 54602 /Cr-2460, with same data as the holotype ; paratypes: 16 females, Х 54603 /Cr-2461, with same data as the holotype .

Addition material. 1 female, 2.6 mm, Х 54604 /Cr-2462, Sea of Japan, Strait of Tartary, shelf of western Sakhalin Island, (47°02'55"N 142°02'49"E, 4 m), coarse sand, on S. intermedius , 09 September 2021, collector A.V. Ushakov ; 2 females, Х 54605 /Cr-2463, with same data as Х 54604/Cr-2462 .

Diagnosis. Rostrum small, as long as lateral head lobe, lateral head lobe with subrectangular corner. Eye large, deep, suboval, white when alive, black in alcohol. Antenna 1 about as long as antenna 2, accessory flagellum minute, one-articulate; flagellum with 5–6 articles. Antenna 2: flagellum with 5 articles. Upper lip: medial notch shallow. Mandible: palp article 2 with setae, palp article 3 1.27 times as long as article 2, accessory spine row with 12 slender blades on right and 8 slender blades on left. Maxilla 1: outer plate with 16 rigid setae. Maxilla 2: outer plate with 7–9 stout spine-like setae. Maxilliped: inner plate with 3 small button-shaped apical setae (spines), outer plate with 1 heavy and 1 small apical setae, palp article 3 short and wide, expanded medially. Pereopod 1 (gnathopod 1): propodus with 2 groups of long setae along posterior margin. Pereopod 2 (gnathopod 2): basis with setae sparsely scattered along anterior margin, propodus with 3 groups of long setae along posterior margin. Pereopods 3 and 4: basis with setae sparsely scattered along anterior margin. Pereopods 5–7: posterodistal lobe of basis roundly truncate. Dactylus of pereopods 3–7 short, stout, inner margin finely crenulate. Pleopods 1 and 2: outer ramus with 9–10 articles. Uropod 1: outer ramus slightly shorter than inner ramus. Telson 1.5 times as long as wide.

Description. Female (3.1 mm). Brightly coloured when alive. Head and pereonites 1–5 with a transverse brown stripe for each. Coxal plates 1–3 with 2 submarginal brown stripes looped ventrally. Coxal plate 4 with 3 stripes. Pereonites 6, 7, pleonites, urosomites, pereopods 5–7 and uropods with blurred brown pattern. Flagella of antennae 1 and 2 with a red band at the middle and with red tip. Body colourless in alcohol. Pereonites, pleonites, and urosomites dorsally smooth.

Head: length exceeding pereonites 1 and 2 together; eye large, suboval; rostrum blunt, high, reaching about 0.5 times of antenna 1 peduncular article 1; lateral head lobe subrectangular. Antenna 1 short, pediform; length ratio of peduncular articles 1–3 as 1.00:0.53:0.22; flagellum short, 0.74 times as long as peduncle, articles 1, 3, 5, 6 with 1–2 aesthetascs for each. Antenna 2: peduncular articles 5 subequal to article 4 in length, articles 1–3 combined shorter than article 4. Upper lip: apically bilobate, without setae. Lower lip: outer lobes horizontal. Mandible: molar tuberculate, smooth; incisor with 7–8 teeth, posterior tooth styliform; left lacinia 6-dentate, right lacinia absent; palp large, length ratio of articles 1–3 as 1.0:1.7:2.6; inner margin of palp article 3 lined with 4 strong pectinate D-setae, apex with 3 long and 1 short E-setae, A-seta absent; article 2 with 2 setae at distal half of inner margin; article 1 without setae. Maxilla 1: inner plate with single plumose apical seta; apex of palp obliquely rounded, with row of 4 spine-like setae ( Watling 1989: type IIA3). Maxilla 2: inner plate slightly shorter than outer plate; inner margin distally with single strong plumose seta. Maxilliped: inner plate short, not reaching proximal margin of palp article 1, apex subrounded, with 2 short setae and 3 button-shaped setae; outer plate short, reaching about 1/2 length of palp article 2, apex rounded, inner margin with submarginal row of 4 short simple setae; palp, length ratio of articles 1–4 as 1.0:1.1:1.1:1.3, inner margin of article 3 with 6 setae and numerous setules; article 4 slender, with dense row of setules along inner margin.

Coxal plates 1–4 increasing in depth from 1 to 4. Coxal plate 1 slightly expanded ventrally, with rounded ventral margin, posteroventrally with 2–3 small teeth. Coxal plates 2–3 deep, ventral margins rounded, posteroventrally with 2 small teeth for each; coxal plate 4 deeply excavate posteroproximally; coxae 5–6 posterolobate, coxa 5, anterior margin rounded, bare, posterior lobe without fine setae; coxa 6 bare or with a few setae along anterior margin, without fine setae on posterior margin; coxa 7 roundly rectangular, with a few fine setae ventrally. Coxal gills on pereopods 2–6, medium in size, sac-like.

Pereopod 1 (gnathopod 1): basis, anterior margin with a few long setae at proximal half, posterior margin weakly expanded proximally, with sparsely scattered setae or bare; ischium short, with posterodistal seta; merus, distal margin with row of long setae, posterior margin with single seta midway; carpus 1.8 times as long as wide, posterior margin with 2 groups of plumodenticulate setae ( Watling 1989: type IA3), with distal row of plumodenticulate setae and 2 stout comb setae; propodus 0.9 times as long as carpus, 1.9 times as long as wide, anterior and posterior margins subparallel, posterior margin with group of 2 spine-like setae near palmar angle, palm slightly oblique; dactylus stout, exceeding palm, 0.44 times as long as propodus. Pereopod 2 (gnathopod 2): basis, with setae sparsely scattered along anterior margin; ischium short, with posterodistal seta; merus, distal margin with row of setae, posterior margin with seta midway; carpus long, 2.4 times as long as wide, posterior margin with 2 groups of setae, with distal row of simple setae and 1 comb seta; propodus 0.85 times as long as carpus, 2.1 times as long as wide, anterior and posterior margins subparallel, posterior margin with row of 2 spine-like setae near palmar angle, palm slightly oblique; dactylus stout, subequal to palm in length, 0.42 times as long as propodus.

Pereopods 3–4 similar, length ratio from basis to dactylus 1.00:0.25:0.58:0.42:0.56–0.63:0.25; basis linear, with setae sparsely scattered along anterior and posterior margins; merus anterodistally produced to 1/4–1/3 of carpus length, acute; posterior margin of carpus with 4–5 short spine-like setae; posterior margin of propodus with 12–13 short spine-like setae; dactylus stout, 0.40–0.45 times as long as propodus. Pereopods 5–7 closely homopodous, length ratio from basis to dactylus 1.00:0.26:0.68–0.86:0.52:0.61–0.73:0.23–0.31; basis, posterior lobe slightly truncate; merus posterodistally produced to 3/5 of carpus length, acute, anterior margin with 7–8 short spine-like setae; carpus, anterior margin with 7–9 short spine-like setae; propodus 2.5 times as long as wide, anterior margin with 7–8 (pereopod 5), 10 (pereopod 6) and 8–9 (pereopod 7) short spine-like setae; dactylus stout, 0.37–0.44 times as long as propodus.

Epimeral plates 1–3: ventral margin with short 1–2 spine-like setae, posteroventral corner with short protrusion, posterior margin with single seta (plates 1 and 2), without serration. Pleopods regular, basal article of inner ramus with 2–3 stout two-pointed plumose setae (coupling setae) along inner margin; outer ramus with 9–10 articles, inner ramus with 8 (pleopods 1 and 2) and 7 (pleopod 3) articles.

Uropod 1: peduncle almost as long as inner ramus; outer ramus shorter, 0.9 times as long as inner ramus; margins of peduncle and rami with serially-arranged numerous short spine-like setae. Uropod 2: inner ramus 1.4 times as long as peduncle, outer ramus 0.7 times as long as inner. Uropod 3: inner ramus 1.9 times as long as peduncle, with row of 4–5 small spine-like setae along lateral and medial margins for each, with acute and non-spinose apex; outer ramus about 0.5 times as long as inner, with 1–2 small spine-like setae along lateral margin and 1 small spine-like seta on medial margin, with acute and non-spinose apex. Telson linguiform, with ventral keel, dorsal surface with 2 sublateral groups of 2 penicillate setae, with 2 rows of microscopic setules in proximal part.

Male unknown.

Type locality. Northwest of Pacific Ocean, Sea of Okhotsk, shelf of southern Sakhalin, Aniva Bay , (46°36'35"N 142°59'57"E, littoral).

Etymology. Named from Latin “ornata” (adorned) according to colouring when alive.

Ecology. Dactylopleustes ornatus sp. nov. was found on sands, shell rock and rock in the depths of 0–5 m, commensal on sea urchin Strongylocentrotus intermedius .

Distribution. Northwest of Pacific Ocean, Sea of Okhotsk, Sea of Japan, shelf of southern Sakhalin Island.

Remarks. Dactylopleustes ornatus sp. nov. is morphologically close to the species group with short, pediform antennae 1 and 2: D. awatschensis sp. nov., D. echinoicus , D. echinoides , D. obsolescens and D. ochotensis sp. nov. From D. okhotensis sp. nov., D. ornatus sp. nov. differs by the maxilla 2 outer plate with 7–9 stout apical spine-like setae (6 spine-like apical setae in D. okhotensis sp. nov.), the apex of maxilliped outer plate with 1 heavy and 1 small apical setae (2 heavy and 1 small setae in D. okhotensis sp. nov.), and the shorter and stout maxilliped palp article 3 (long and narrow in D. okhotensis sp. nov.). Dactylopleustes ornatus sp. nov. differs from D. awatschensis sp. nov., D. echinoicus , D. echinoides and D. obsolescens in the same set of characters as D. ochotensis sp. nov.

Figures

FIGURE 1. Species of Dactylopleustes Karaman & Barnard, 1979, lateral view:a—D. longoantennis sp. nov., b—D. tzvetkovae sp. nov., c—D. yoshimurai Tomikawa, Hendrycks & Mawatari, 2004 (from Tomikawa et al. 2004: fig. 1), d—D. obsolescens Hirayama, 1988 (from Hirayama 1988: fig. 269), e—D. awatschensis sp. nov., f—D. okhotensis sp. nov., g—D. echinoides Bousfield & Hendrycks, 1995 (from Bousfield & Hendrycks 1995: fig. 40), h—D. ornatus sp. nov.

FIGURE 2. Dactylopleustes spp.: antenna 1—a–i; antenna 2—j–r: a, j—D. longoantennis sp. nov., b, k—D. tzvetkovae sp. nov., c, l—D. yoshimurai (from Tomikawa et al. 2004: fig. 1), d, m—D. echinoicus (from Tzvetkova 1975), e, n—D. obsolescens (from Hirayama 1988: fig. 270), f, o—D. awatschensis sp. nov., g, p—D. okhotensis sp. nov., h, q—D. echinoides (from Bousfield & Hendrycks 1995: fig. 40), i, r—D. ornatus sp. nov.

FIGURE 3. Dactylopleustes spp.: mandible—a–k; maxilla 1—l–t: a, b, l—D. longoantennis sp. nov., c, m—D. tzvetkovae sp. nov., d, e, n—D. yoshimurai (from Tomikawa et al. 2004: fig. 1), f, o—D. echinoicus (from Tzvetkova 1975), g, p—D. echinoides (from Bousfield & Hendrycks 1995: fig. 40), h, q—D. awatschensis sp. nov., i, r—D. ornatus sp. nov., j, s—D. okhotensis sp. nov., k, t—D. obsolescens (from Hirayama 1988: fig. 270).

FIGURE 4. Dactylopleustes spp.: maxilla 2—a–i; outer plates of maxilliped—j–r: a, j—D. longoantennis sp. nov., b, k—D. tzvetkovae sp. nov, c, l—D. yoshimurai (from Tomikawa et al. 2004: fig. 1), d, m—D. echinoicus (from Tzvetkova 1975), e, n—D. echinoides (from Bousfield & Hendrycks 1995: fig. 40), f, o—D. awatschensis sp. nov., g, p—D. ornatus sp. nov., h, q—D. okhotensis sp. nov., i, r—D. obsolescens (from Hirayama 1988: fig. 270).

FIGURE 5. Dactylopleustes spp.: pereopod 1 (gnathopod 1)—a–i; pereopod 2 (gnathopod 2)—j–r: a, j—D. longoantennis sp. nov., b, k—D. tzvetkovae sp. nov., c, l—D. yoshimurai (from Tomikawa et al. 2004: fig. 2), d, m—D. echinoicus (from Tzvetkova 1975), e, n—D. echinoides (from Bousfield & Hendrycks 1995: fig. 40), f, o—D. awatschensis sp. nov., g, p—D. ornatus sp. nov., h, q—D. okhotensis sp. nov., i, r—D. obsolescens (from Hirayama 1988: fig. 270).

FIGURE 6. Dactylopleustes spp.: pereopod 4: a, b—D.longoantennis sp. nov., c, d—D. tzvetkovae sp. nov., e, f—D.yoshimurai (from Tomikawa et al. 2004: fig. 2), g—D. echinoicus (from Tzvetkova 1975), h—D. echinoides (from Bousfield & Hendrycks 1995: fig. 40), i, j—D. awatschensis sp. nov., k, l—D. ornatus sp. nov., m—D. okhotensis sp. nov., n—D. obsolescens (from Hirayama 1988: fig. 270).

FIGURE 7. Dactylopleustes spp.: pereopod 5: a, b—D.longoantennis sp. nov., c, d—D. tzvetkovae sp. nov., e, f—D.yoshimurai (from Tomikawa et al. 2004: fig. 2), g—D. echinoicus (from Tzvetkova 1975), h, i—D. echinoides (from Bousfield & Hendrycks 1995: fig. 40; Tomikawa et al. 2004: fig. 6), j, k—D. awatschensis sp. nov., l, m—D. ornatus sp. nov., n—D. okhotensis sp. nov., o—D. obsolescens (from Hirayama 1988: fig. 270).

FIGURE 8. Dactylopleustes spp.: pleopods—a–g; uropod 1—h–n: a, h—D. longoantennis sp. nov., b, i—D. tzvetkovae sp. nov., c, j—D. yoshimurai (from Tomikawa et al. 2004: fig. 5), d, k—D. awatschensis sp. nov., e, l—D. ornatus sp. nov., f, m—D. okhotensis sp. nov., g, n—D. obsolescens (from Hirayama 1988: fig. 271).

FIGURE 24. Dactylopleustes ornatus sp. nov., holotype, female (3.1 mm): a—lateral view, coloration when a live; paratype, female (2.9 mm): b—dorsal view, coloration of the alcohol fixed sprcimen.

FIGURE 25. Dactylopleustes ornatus sp. nov., holotype, female (3.1 mm): a—lateral view, b—antenna 1, c—aesthetascs of antenna 1 flagellum, d—antenna 2, e—upper lip, f—left mandible, g—incisor and molar of left mandible, h—incisor and molar of right mandible, i—lower lip, j—maxilla 1, k—maxilla 2; scales: a—0.5 mm, b–k—0.1 mm.

FIGURE 26. Dactylopleustes ornatus sp. nov., holotype, female (3.1 mm): a—maxilliped, b—inner and outer plates of maxilliped, c—pereopod 1, d, e—posterodistal corner of coxal plate 1, f—pereopod 1, inner side; paratype, female (2.9 mm): g—maxilliped, h—inner and outer plates of maxilliped; scale—0.1 mm.

FIGURE 27. Dactylopleustes ornatus sp. nov., holotype, female (3.1 mm): a—pereopod 2, inner side, b—propodus and dactylus of pereopod 2, inner side, c—pereopod 3; d—propodus and dactylus of pereopod 3, e—pereopod 4, f—propodus and dactylus of pereopod 4; scale—0.1 mm.

FIGURE 28. Dactylopleustes ornatus sp. nov., holotype, female (3.1 mm): a—pereopod 5, b—propodus and dactylus of pereopod 5, c—dactylus of pereopod 5 (opposite leg), d—pereopod 6, e—propodus and dactylus of pereopod 6, f—pereopod 7, g—propodus and dactylus of pereopod 7, h, i, j—epimeral plates 1–3; scale—0.1 mm.

FIGURE 29. Dactylopleustes ornatus sp. nov., holotype, female (3.1 mm): a—pleopod 1, b—retinacula (coupling spines) of pleopod 1, c—coupling setae of pleopod 1, d—pleopod 2, e—coupling setae of pleopod 2, f—pleopod 3, g—uropod 1, h—uropod 2, i, j—uropod 3; paratype, female (2.9 mm): k—telson; scale—0.1 mm.

FIGURE 30. Dactylopleustes ornatus sp. nov., paratype, female (3.5 mm): a—lateral view, b—dactylus of pereopods 5 and 6.

FIGURE 36. Distribution of Dactylopleustes species.