Dactylopleustes awatschensis, 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 : 205-220

Dactylopleustes awatschensis sp. nov.

Figures 1e , 2f, o , 3h, q , 4f, o , 5f, o , 6i, j , 7j, k , 8d, k , 9–13 , 36

Type material. Holotype: female, 5.05mm,Х54598/Cr-2456, Pacific Ocean ,shelf of the eastern Kamchatka Peninsula, Avacha Bay, Vilyuchinskaya Bay (52°37'007"N 158°27'026"E, 7 m), stones with shells, on Strongylocentrotus polyacanthus A. Agassiz & H.L. Clark, 1907 , 17 October 2022, collector D.D. Danilin. Paratypes: 1 female, 3.7 mm, Х 54599/Cr-2457, Pacific Ocean, shelf of the eastern Kamchatka Peninsula , Avacha Bay , Vilyuchinskaya Bay (52°36'52"N 158°29'46"E, 10.5 m), stones with shells, on S. polyacanthus , 21 April 2022, collector D.D. Danilin. Paratypes: 4 females, Х 54600/Cr-2458, with the same data as paratype Х 54599/Cr-2457 .

Diagnosis. Rostrum small, as long as lateral head lobe, lateral head lobe with rectangular anterior corner. Eye large, deep, reniform, 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 4–5 articles. Upper lip: medial notch shallow. Mandible: palp article 2 with setae, as long as article 3, accessory spine row with 11 slender blades on right and 6 on left. Maxilla 1: outer plate with 17 rigid setae. Maxilla 2: outer plate with 11 stout spine-like setae. Maxilliped: inner plate with 2 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 3 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 distal part of anterior margin. Pereopods 5–7: posterodistal lobe of basis rounded. Dactylus of pereopods 3–7 short, stout, inner margin finely crenulate. Pleopod 1 and 2: outer ramus with 11 articles. Uropod 1: outer ramus slightly shorter than inner ramus. Telson 1.6 times as long as wide.

Description. Female (5.05 mm). Body colourless in alcohol. Pereonites, pleonites, and urosomites dorsally smooth.

Head: length (excluding rostrum) exceeding pereonite 1; eye large, reniform; rostrum blunt, long, reaching about 0.5 times of antenna 1 peduncular article 1; lateral head lobe rectangular. Antenna 1 short, pediform; length ratio of peduncular articles 1–3 as 1.00:0.44:0.21; flagellum short, 0.66 times as long as peduncle, articles 1–3 with 1 aesthetasc for each. Antenna 2: peduncular article 5 slightly shorter than article 4, articles 1–3 combined shorter than article 4; article 2 with long posterodistal protrusion, subequal to article 3 length. Upper lip apically bilobate and slightly asymmetrical, without setae. Mandible: molar tuberculate, smooth; incisor with 7–8 teeth; left lacinia 6-dentate, right lacinia absent; palp large, length ratio of articles 1–3 as 1.0:2.8:2.7; inner margin of palp article 3 lined with 4 strong pectinate D-setae, apex with 1 long and 3 short E-setae, A-seta absent; article 2 with 4 plumose setae along 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 5 spine-like setae ( Watling 1989: type IIA3). Maxilla 2: inner plate slightly shorter and broader than outer plate; inner margin distally with single strong plumose seta. Maxilliped: inner plate short, reaching proximal margin of palp article 1, apex truncate, distally with 3 short setae and 2 button-shaped setae; outer plate short, exceeding palp article 1, outer margin rounded, inner margin with submarginal row of short simple setae sparsely scattered along margin; palp narrow, length ratio of articles 1–4 as 1.0:1.1:1.2:1.2, inner margin of article 3 with a few 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 3, coxal plate 4 as deep as plate 3. Coxal plate 1 with subparallel anterior and posterior margins, with rounded ventral margin, posteroventrally with 2–3 small teeth. Coxal plates 2–3 deep, ventral margins subrounded, plate 2 posteroventrally with 2–3 small teeth, plate 3 posteroventrally with 3 small teeth; coxal plate 4 broader, deeply excavate posteroproximally; coxae 5–7 posterolobate, coxa 5, anterior margin rounded, bare, posterior lobe with fine setae; coxa 6 with a few setae along anterior margin and with fine setae along posterior margin; coxa 7 with fine setae along posterior margin. Coxal gills on pereopods 2–6, medium in size, sac-like, with thin marginal filaments. Brood plates on pereopods 2–5, large in pereopod 4, leaf-shaped.

Pereopod 1 (gnathopod 1): basis, anterior margin setose, posterior margin weakly expanded, with setae sparsely scattered along margin; ischium short, with posterodistal seta; merus, distal margin with row of setae; carpus, 2.1 times as long as wide, with 2 setae along anterior margin, posterior margin densely setose; propodus narrowly subrectangular, 0.84 times as long as carpus, 2.5 times as long as wide, posterior margin with 2 spine-like setae near palmar angle, palm slightly oblique; dactylus stout, overhanging palm, 0.45 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 group of 2 setae midway; carpus long, 2.5 times as long as wide, posterior and distal margins densely setose, distal margin with 2 strong plumose setae; propodus narrowly subrectangular, 0.87 times as long as carpus, 2.4 times as long as wide, posterior margin with 2 spine-like setae near palmar angle, palm slightly oblique; dactylus stout, overhanging palm, 0.43 times as long as propodus.

Pereopods 3–4 similar, length ratio from basis to dactylus 1.00:0.28:0.66:0.45:0.60:0.24; basis linear, with setae sparsely scattered along distal part of anterior margin; merus anterodistally produced to 1/3 of carpus length, acute; posterior margin of carpus with 9–10 short spine-like setae; posterior margin of propodus with 16 (pereopod 3)—22 (pereopod 4) short spine-like setae; dactylus stout, 0.35–0.40 times as long as propodus. Pereopods 5–7 closely homopodous, length ratio from basis to dactylus 1.00:0.25:0.74:0.48:0.69:0.32; basis, posterior lobe rounded and minutely serrated; merus posterodistally produced to 1/3–2/5 of carpus length, acute, anterior margin with 6–9 short spine-like setae; carpus, anterior margin with 7–11 short spine-like setae; propodus 4.1 times as long as wide, anterior margin with 15 (pereopod 5), 17 (pereopod 6) and 17 (pereopod 7) short spine-like setae; dactylus stout.

Epimeral plates 1–3, ventral margin with short spine-like setae, posteroventral corners subacute, posterior margins 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 (pleopods 1 and 2) and 10 (pleopod 3) articles, inner ramus with 10 (pleopods 1 and 2) and 8–9 (pleopod 3) articles.

Uropod 1: peduncle 1.33 times as long as inner ramus; outer ramus 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 1.1 times as long as peduncle, outer ramus 0.8 times as long as inner. Uropod 3: inner ramus 1.9 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 2 small spine-like setae along lateral and medial margins for each, with acute and non-spinose apex. Telson linguiform, with ventral keel, dorsal surface with 2 setae in distal half and 4 penicillate setae in proximal half, lateral margins parallel.

Marsupium contained 2 juveniles of 1.1 mm length.

Male unknown.

Type locality. Pacific Ocean, shelf of the eastern Kamchatka Peninsula, Avacha Bay, Vilyuchinskaya Bay (52°37'007"N 158°27'026"E, 7 m) .

Etymology. Named after the type locality in Avacha Bay.

Ecology. Dactylopleustes awatschensis sp. nov. was found in the depths of 7–10.5 m on stones with shells, commensal on sea urchin Strongylocentrotus polyacanthus . Females with juveniles in marsupium were found in October.

Distribution. Known only from the type locality.

Remarks. Dactylopleustes awatschensis sp. nov. is morphologically close to the group of species with short, pediform antennae 1 and 2: D. echinoicus , D. echinoides , D. obsolescens , D. okhotensis sp. nov. and D. ornatus sp. nov. Dactylopleustes awatschensis sp. nov. differs from D. echinoides by the poorly setose bases of gnathopod 2 and pereopods 3–4 (strongly setose anteriorly in D. echinoides ). From D. obsolescens the new species differs by the mandibular palp article 3 shorter than articles 1 and 2 together (longer in D. obsolescens ), the propodus of gnathopod 2 with 3 groups of long setae along posterior margin (2 groups in D. obsolescens ). From D. okhotensis sp. nov. and D. ornatus sp. nov. the new species differs by the apex of maxilliped outer plate with 2 heavy and 1 small apical setae (1 heavy and 1 small apical setae in D. ornatus sp. nov.), and by the propodus of gnathopod with 3 groups of long setae along posterior margin (2 groups in other species). Dactylopleustes awatschensis sp. nov. differs from D. echinoicus by the antenna 1 flagellum with 6 or fewer articles (8 articles in D. echinoicus ) and by the mandibular palp article 3 subequal to article 2 in length (2 times as long as article 2 in D. echinoicus ).

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 9. Dactylopleustes awatschensis sp. nov., holotype, female (5.05 mm): a—lateral view, b—antenna 1, c—accessory flagellum of antenna 1, d—antenna 2, e—upper lip, f—left mandible, g—right mandible; paratype, female (3.7 mm): h—lateral view, i—antenna 1, j—antenna 2; scales: h—1 mm, a—0.5 mm, b–g, i, j—0.1 mm.

FIGURE 10. Dactylopleustes awatschensis sp. nov., holotype, female (5.05 mm): a—maxilla 1, b—maxilla 2, c—maxilliped, d—outer plates of maxilliped, e—pereopod 1, outer side, f—propodus and dactylus of pereopod 1; paratype, female (3.7 mm): g—aesthetascs of antenna 1 flagellum; scale—0.1 mm.

FIGURE 11. Dactylopleustes awatschensis sp. nov., holotype, female (5.05 mm): a, b—pereopod 2, outer side, c—coxal plate 6 with coxal gill, d—brood plate of pereopod 2, e, f—pereopod 3, g, h—pereopod 4; scales: a, d, e, g—0.2 mm, b, c, f, h—0.1 mm.

FIGURE 12. Dactylopleustes awatschensis sp. nov., holotype, female (5.05 mm): a, b—pereopod 5, c, d—pereopod 6; e, f—pereopod 7, g, h, i—epimeral plates 1–3, j—uropod 1, k—uropod 2, l—uropod 3, m—telson; scales: a, c, e, g, h, i—0.2 mm, b, d, f, j, k, l, m—0.1 mm.

FIGURE 13. Dactylopleustes awatschensis sp. nov., holotype, female (5.05 mm): a, b, c—posterodistal angle of coxal plates 1, 2, 3, d—pleopod 3, e—retinacula (coupling spines) of pleopod 3, f—coupling setae of pleopod 3; scales: d—0.2 mm, a, b, c, e, f—0.1 mm.

FIGURE 36. Distribution of Dactylopleustes species.