Dactylopleustes tzvetkovae, 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 : 243-249

Dactylopleustes tzvetkovae sp. nov.

Figures 1b , 2b, k , 3c, m , 4b, k , 5b, k , 6c, d , 7c, d , 8b, i , 31–35 , 36

Type material. Holotype: female, 3.6 mm, Х 54607 /Cr-2465, Sea of Okhotsk , shelf of south-eastern Sakhalin , (47°54'16.35"N 142°31'30.537"E, 5 m), stones, on Strongylocentrotus intermedius , 12 October 2021, collector A.V. Ushakov.

Diagnosis. Rostrum small, as long as lateral head lobe, lateral head lobe with subacute anterior corner. Eye large, deep, reniform, black in alcohol. Antenna 1 slightly longer than antenna 2, accessory flagellum minute, one-articulate; flagellum medium long, with 12 articles. Antenna 2: flagellum with 8 articles. Upper lip: medial notch shallow. Lower lip: outer lobes horizontal. Mandible: palp article 2 with setae, palp article 3 1.38 times as long as article 2, accessory spine row with 20 slender blades on right and 21 on left. Maxilla 1: outer plate with 23 rigid setae. Maxilla 2: outer plate with 8–11 stout spine-like setae. Maxilliped: inner plate with 5–6 small button-shaped apical setae (spines), outer plate with 2 heavy and 1 small apical setae, palp article 3 long and narrow. 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 4 groups of long setae along posterior margin. Pereopods 3 and 4: anterior margin of basis poorly setose. Pereopods 5–7: posterodistal lobe of basis roundly truncate. Dactylus of pereopods 3–7 short, inner margin finely crenulate. Pleopods 1 and 2: outer ramus with 11 articles. Uropod 1: outer ramus slightly shorter than inner ramus. Telson 1.4 times as long as wide.

Description. Female (3.6 mm). Body colourless in alcohol. Pereonites, pleonites, and urosomites dorsally smooth.

Head: length (excluding rostrum) exceeding pereonites 1 and 2 together; eye large, reniform; rostrum acute, long, reaching about 0.5 length of antenna 1 peduncular article 1; lateral head lobe subacute. Antenna 1 long, not pediform; length ratio of peduncular articles 1–3 as 1.00:0.52:0.22; flagellum long, 1.05 times as long as peduncle, articles with 3 aesthetascs for each. Antenna 2: peduncular article 5 slightly shorter than article 4, articles 1–3 combined as long as article 4. Mandible: molar tuberculate, smooth; incisor with 6–7 teeth; left lacinia 7-dentate, right lacinia absent; palp large, length ratio of articles 1–3 as 1.0:3.0:4.1; inner margin of palp article 3 lined with 6 strong pectinate D-setae, apex with 3 short and 1 long E-setae, A-seta absent, medial surface with field of numerous setules; article 2 with 5 setae along distal half of inner margin; article 1 without setae. Maxilla 1: inner plate with single strong plumose apical seta; apex of palp rounded, with row of 6 spine-like setae ( Watling 1989: type IIA3). Maxilla 2: inner plate 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 obliquely truncate, with 2 short setae and 5–6 button-shaped setae; outer plate short, reaching about 1/2–2/3 length of palp article 2, outer margin rounded, inner margin slightly concave, with submarginal row of sparsely scattered short simple setae; palp narrow, length ratio of articles 1–4 as 1.0:1.0:1.3:1.5, inner margin of article 3 with 7 setae and submarginal field of numerous small spine-like setules; article 4 slender, slightly curved inside, with dense row of small spine-like setules along inner margin.

Coxal plates 1–4 increasing in depth from 1 to 4. Coxal plate 1 slightly expanding distally, with rounded ventral margin, posteroventrally with 3 small teeth. Coxal plates 2–3 deep, ventral margins subrounded, posteroventrally with 2–3 small teeth for each; coxal plate 4 broader, deeply excavated in proximal 1/3 posteriorly; coxae 5–7 posterolobate, coxa 5, anterior margin rounded, bare, posterior lobe with single fine seta ventrally; coxa 6 with a few setae along anterior margin and with single fine seta on posterior lobe ventrally; coxa 7 with fine setae along posterior margin. Coxal gills on pereopods 2–6, medium in size, large in pereopod 4, sac-like.

Pereopod 1 (gnathopod 1): basis, anterior and posterior margins setose, posterior margin weakly expanded; ischium short, with 1–2 posterodistal setae; merus, distal margin with row of setae, with 3 strong setae along posterior margin; carpus 2.2 times as long as wide, with 2 setae along anterior margin, posterior margin with 3 groups of plumose setae, with dense row of plumose setae and 2 stout comb setae posterodistally, medial surface with 3 transverse groups of 2–3 setae along posterior margin; propodus with subparallel margins, 0.86 times as long as carpus, 2.3 times as long as wide, posterior margin with 2 spine-like setae near palmar angle, medial surface with oblique row of 3 setae, palm oblique, roundly passing to posterior margin; dactylus slightly longer than palm, 0.4 times as long as propodus. Pereopod 2 (gnathopod 2): basis, anterior and posterior margins poorly setose; ischium short, with 1–2 posterodistal setae; merus, distal margin with row of sparsely scattered setae, with 2 long setae along posterior margin; carpus long and narrow, 2.6 times as long as wide, posterior margin with 3–4 groups of long setae, with dense row of long setae and single stout comb seta posterodistally; propodus slightly narrowed distally, 0.9 times as long as carpus, 2.7 times as long as wide, posterior margin with 4–5 spine-like setae near palmar angle, palm strongly oblique, roundly passing to posterior margin; dactylus short, shorter than palmar margin, 0.33 times as long as propodus.

Pereopods 3–4 similar, length ratio from basis to dactylus 1.00:0.22:0.68:0.48:0.67:0.29; basis sublinear, anterior and posterior margins setose; merus anterodistally produced to 1/4 of carpus length; posterior margin of carpus with 7–8 short spine-like setae; posterior margin of propodus with 14–15 short spine-like setae; dactylus stout, 0.43–0.45 times as long as propodus. Pereopods 5–7 closely homopodous, length ratio from basis to dactylus 1.00:0.29:0.70– 0.92:0.48–0.54:0.70–0.82:0.31–0.41; basis, posterodistally lobe roundly truncate; merus posterodistally produced to 2/5–1/2 of carpus length, anterior margin with 6–11 short spine-like setae; carpus, anterior margin with 7–9 short spine-like setae; propodus 3.0 times as long as wide, anterior margin with 14 short spine-like setae; dactylus stout, 0.44–0.49 times as long as propodus.

Epimeral plates 1–3: ventral margin with1 (plate 1), 4 (plate 2)and 3(plate 3) short spine-like setae, posteroventral corner subacute, posterior margin without serration. Pleopods regular, basal article of inner ramus with 3 stout two-pointed plumose setae (coupling setae) along inner margin; outer ramus with 11 (pleopod 1), 11 (pleopod 2) and 9 (pleopod 3) articles, inner ramus with 10 (pleopod 1), 9 (pleopod 2) and 8 (pleopod 3) articles.

Uropod 1: peduncle 0.94 times as long as inner ramus; outer ramus 0.89 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 0.73 times as long as inner. Uropod 3: inner ramus 2.0 times as long as peduncle, with row of 5–6 small spine-like setae along lateral and medial margins for each, with acute and non-spinose apex; outer ramus about 0.6 times as long as inner, with 4 small spine-like setae along lateral margin and single seta on medial margin, with acute and non-spinose apex. Telson linguiform, with ventral keel, dorsal surface with 2 groups of 2 penicillate setae and with 2 short setae.

Male unknown.

Type locality. Sea of Okhotsk, shelf of south-eastern Sakhalin Island , (47°54'16.35"N 142°31'30.537"E, 5 m).

Etymology. Named in memory of famous Russian carcinologist Nina L. Tzvetkova.

Ecology. Dactylopleustes tzvetkovae sp. nov. was found on stones in the depth of 5 m, commensal on sea urchin Strongylocentrotus intermedius .

Distribution. Known only from the type locality.

Remarks. Dactylopleustes tzvetkovae sp. nov. is morphologically close to the species group with plesiomorphic long antennae 1 and 2: D. longoantennis sp. nov. and D. yoshimurai . Dactylopleustes tzvetkovae sp. nov. differs from D. longoantennis sp. nov. by the flagellum of antenna 1 and 2 consisting of 12 and 8 articles respectively (17 and 14 in D. longoantennis sp. nov.), the apex of maxilliped outer plate with 2 heavy and 1 small apical setae (3 heavy setae in D. longoantennis sp. nov.), the posterior margin of propodus of gnathopods 1 and 2 with 2 and 4 groups of setae respectively (3 and 5 in D. longoantennis sp. nov.). Dactylopleustes tzvetkovae sp. nov. differs from D. yoshimurai by the flagellum of antenna 1 consisting of 12 articles (8 in D. yoshimurai ), the apex of maxilliped outer plate with 2 heavy and 1 small apical setae (1 heavy and 1 small setae in D. yoshimurai ), and the maxilla 1 outer plate with 23 rigid apical setae (17–18 in D. yoshimurai ).

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 31. Dactylopleustes tzvetkovae sp. nov., holotype, female (3.6 mm): a, b—lateral view, c—antenna 1, d—antenna 2; scale—0.5 mm.

FIGURE 32. Dactylopleustes tzvetkovae sp. nov., holotype, female (3.6 mm): a—aesthetascs of antenna 1 flagellum, b—left mandible, c—incisor of right mandible, d—lower lip, e—maxilla 1, f—maxilla 2, g—maxilliped, h—inner plate of maxilliped, i—outer plates of maxilliped; scale—0.1 mm.

FIGURE 33. Dactylopleustes tzvetkovae sp. nov., holotype, female (3.6 mm): a, b—pereopod 1, outer side, c—pereopod 1, inner side, d, e—pereopod 2, outer side, f, g—pereopod 3; scales: a, d, f—0.5 mm, b, c, e, g—0.1 mm.

FIGURE 34. Dactylopleustes tzvetkovae sp. nov., holotype, female (3.6 mm): a—posterodistal angles of coxal plates 1–3, b, c—pereopod 4, d, e—pereopod 5, f, g—pereopod 6, h, i—pereopod 7, j, k, l—epimeral plates 1–3; scales: b, d, f, h, j, k, l—0.5 mm, a, c, e, g, i—0.1 mm.

FIGURE 35. Dactylopleustes tzvetkovae sp. nov., holotype, female (3.6 mm): a—pleopod 1, b—retinacula (coupling spines) of pleopod 1, c—pleopod 2, d—retinacula (coupling spines) of pleopod 2, e—pleopod 3, f—coupling setae of pleopod 3, g—uropod 1, h—uropod 2, i—uropod 3, j—telson; scales: a, c, e, g, h, i—0.5 mm, b, d, f, j—0.1 mm.

FIGURE 36. Distribution of Dactylopleustes species.