Dactylopleustes okhotensis, Labay, 2025

Dactylopleustes okhotensis sp. nov.

Figures 1f View FIGURE 1 , 2g, p View FIGURE 2 , 3j, s View FIGURE 3 , 4h, q View FIGURE 4 , 5h, q View FIGURE 5 , 6m View FIGURE 6 , 7n View FIGURE 7 , 8f, m View FIGURE 8 , 19–23 View FIGURE 19 View FIGURE 20 View FIGURE 21 View FIGURE 22 View FIGURE 23 , 36

Type material. Holotype: male, 3.4 mm, Х 54608 View Materials /Cr-2466, Sea of Okhotsk , shelf of the western Kamchatka Peninsula (56°13'34"N 155°23'07"E, 52 m), sand, 04 August 2020, collector N. V. Shalaputin. GoogleMaps

Diagnosis. Rostrum small, as long as lateral head lobe, lateral head lobe with rectangular corner. Eye large, deep, weakly 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 deep. Mandible: palp article 2 with setae, palp article 3 1.48 times as long as article 2, accessory spine row with 8 slender blades on right and 6 blades on left. Maxilla 1: outer plate with 15 rigid setae. Maxilla 2: outer plate with 6 stout spine-like setae. Maxilliped: inner plate with 3 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 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 rounded. Dactylus of pereopods 3–7 short, stout, inner margin finely crenulate. Pleopods 1 and 2: outer ramus with 8–10 articles. Uropod 1: outer ramus slightly shorter than inner ramus. Telson 1.5 times as long as wide.

Description. Male (3.4 mm). Body colourless in alcohol. Pereonites, pleonites, and urosomites dorsally smooth.

Head: length (excluding rostrum) exceeding pereonites 1 and 2 together; eye large, weakly reniform; rostrum, blunt, long, reaching about 1/3 length of antenna 1 peduncular article 1; lateral head lobe rectangular.Antenna 1 short, pediform; length ratio of peduncular articles 1–3 as 1.00:0.58:0.25; flagellum short, 0.67 times as long as peduncle, articles 1–4 with 2 aesthetascs 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. Lower lip: outer lobes horizontal. Mandible: molar tuberculate, smooth; incisor with 7–8 teeth, posterior tooth styliform; left lacinia 5-dentate, right lacinia absent; palp large, length ratio of articles 1–3 as 1.0:2.1:3.1; inner margin of palp article 3 lined with 3 strong pectinate D-setae, apex with 4 long E-setae, A-seta absent; article 2 with 1–2 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 5–6 spine-like setae ( Watling 1989: type IIA3). Maxilla 2: inner plate slightly longer than and as broad as 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 1/4–1/3 length of palp article 2, outer margin rounded, inner margin slightly concave, with 1 marginal and 2 facial short simple setae; palp narrow, length ratio of articles 1–4 as 1.0:0.9:1.3:1.3, inner margin of article 3 with 3 setae and numerous spine-like setules; article 4 slender, finely pectinate, with dense row of setules along inner margin.

Coxal plates 1–4 increasing in depth from 1 to 4. Coxal plate 1 with subparallel anterior and posterior margins, with rounded ventral margin, posteroventrally with 2 small teeth. Coxal plates 2–3 deep, ventral margins subrounded, plate 2 posteroventrally with 2 small teeth, plate 3 posteroventrally with 1 small tooth; 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.

Pereopod 1 (gnathopod 1): basis, anterior margin setose, posterior margin weakly expanded proximally, without setae; ischium short, with posterodistal seta; merus, distal margin with row of long setae, posterior margin with single seta midway; carpus 1.7 times as long as wide, posterior margin with 1 group of setae midway, distal margin with row of simple setae and 2 strong plumose setae; propodus slightly narrowing distally, 1.1 times as long as carpus, 2.1 times as long as wide, posterior margin with group of 1–2 spine-like setae near palmar angle, palm oblique; dactylus stout, subequal to palm in length, 0.33 times as long as propodus. Pereopod 2 (gnathopod 2): basis, anterior margin with single proximal seta and single anterodistal seta; ischium short, with group of 2 posterodistal setae; merus, distal margin with row of setae, posterior margin with 2 single setae; carpus long, 2.0 times as long as wide, posterior margin with 2 groups of setae, distal margin with row of simple setae and 2 strong plumose setae; propodus slightly narrowing distally, subequal in length to carpus, 2.2 times as long as wide, posterior margin with 2 single spine-like setae near palmar angle, palm oblique; dactylus stout, subequal to palm length, 0.34 times as long as propodus.

Pereopods 3–4 similar, length ratio from basis to dactylus 1.00:0.34:0.63:0.42:0.58–0.69:0.24; basis linear, with setae sparsely scattered along anterior and posterior margins; merus anterodistally produced to 1/5–1/4 of carpus length, acute; posterior margin of carpus with 5–8 short spine-like setae; posterior margin of propodus with 10–12 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 1.00:0.25:0.73:0.48:0.72:0.27; basis, posterior lobe rounded; merus posterodistally produced to 1/2 of carpus length, acute, anterior margin with 6–8 short spine-like setae; carpus, anterior margin with 7–9 short spine-like setae; propodus 2.6 times as long as wide, anterior margin with 13 (pereopod 5), 12 (pereopod 6) and 9 (pereopod 7) short spine-like setae; dactylus stout, 0.35–0.39 times as long as propodus.

Epimeral plates 1–3: ventral margins with short spine-like setae, posteroventral corners with short blunt protrusion, posterior margins with single minute seta, without serration. Pleopods regular, basal article of inner ramus with 3–4 stout two-pointed plumose setae (coupling setae) along inner margin; outer ramus with 7–9 articles, inner ramus with 7–8 (pleopods 1 and 2) and 6 (pleopod 3) articles.

Uropod 1: peduncle 1.2 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 0.9 times as long as inner. Uropod 3: inner ramus 2.2 times as long as peduncle, with row of 3 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 3 small spine-like setae along lateral margin and single small spine-like seta on medial margin, with acute and non-spinose apex. Telson linguiform, with ventral keel, dorsal surface with 2 distal setules and 2 sublateral groups of 2 penicillate setae.

Female unknown.

Type locality. Northwest of Pacific Ocean, Sea of Okhotsk , shelf of the western Kamchatka Peninsula (56°13'34"N 155°23'07"E, 52 m) GoogleMaps .

Etymology. Named after the type locality, Sea of Okhotsk.

Ecology. Dactylopleustes okhotensis sp. nov. was found on sand in the depth of 52 m in the layer of constant low temperature (-1.2-+0.5°C). The host is unknown. This station was dominated by the flat sea urchin Echinarachnius parma (Lamarck, 1816) , but a globular sea urchin Strongylocentrotus pallidus (G.O. Sars, 1872) may also have existed.

Distribution. Known only from the type locality.

Remarks. Dactylopleustes okhotensis 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. ornatus sp. nov. Dactylopleustes okhotensis sp. nov. differs from D. echinoides by the poorly setose bases of gnathopod 2, pereopods 3 and 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 oblique palmar margins of gnathopods 1 and 2 (transverse in D. obsolescens ), and the propodus of gnathopod 2 with 3 groups of long setae along posterior margin (2 groups in D. obsolescens ). Dactylopleustes okhotensis sp. nov. differs from D. awatschensis sp. nov. by the maxilla 2 outer plate with 6 stout spine-like apical setae (8–11 spine-like setae in D. awatschensis sp. nov.), and the gnathopod 1 propodus with 2 groups of long setae along posterior margin (with 3 groups of long setae along posterior margin in other species). From D. ornatus sp. nov. the new species differs by maxilla 2 outer plate with 6 stout spine-like apical setae (7–9 in D. ornatus sp. nov.), 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 the long and narrow palp article 3 of maxilliped (short and stout in D. ornatus sp. nov.).