Dactylopleustes longoantennis, Labay, 2025

Dactylopleustes longoantennis sp. nov.

Figures 1a View FIGURE 1 , 2a, j View FIGURE 2 , 3a, b, l View FIGURE 3 , 4a, j View FIGURE 4 , 5a, j View FIGURE 5 , 6a, b View FIGURE 6 , 7a, b View FIGURE 7 , 8a, h View FIGURE 8 , 14–18 View FIGURE 14 View FIGURE 15 View FIGURE 16 View FIGURE 17 View FIGURE 18 , 36

Type material. Holotype: male, 6.6 mm, Х 54606 View Materials /Cr-2464, Sea of Japan, Strait of Tartary, shelf of western Sakhalin (47°02'50"N 142°02'35"E, 10 m), rocks, on Strongylocentrotus intermedius (A. Agassiz, 1864) , 01 March 2022, collector A. V. Ushakov. GoogleMaps

Diagnosis. Rostrum small, as long as lateral head lobe, lateral head lobe with acute corner. Eye large, deep, reniform, black in alcohol. Antenna 1 about as long as antenna 2, accessory flagellum minute, one-articulate; flagellum long, with 18 articles. Antenna 2: flagellum with 14 articles. Lower lip: outer lobes horizontal. Mandible: palp article 2 with setae, palp article 3 1.36 times as long as article 2, accessory spine row with 27 slender blades on right and 26 on left. Maxilla 1: outer plate with 30 rigid setae. Maxilla 2: outer plate with 14 stout spine-like setae. Maxilliped: inner plate with 6 small button-shaped apical setae (spines), outer plate with 3 heavy 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): anterior margin of basis setose, propodus with 5 groups of long setae along posterior margin. Pereopods 3 and 4: anterior margin of basis densely 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 14–16 articles. Uropod 1: outer ramus slightly shorter than inner ramus. Telson 1.3 times as long as wide.

Description. Male (6.6 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 1/3 length of antenna 1 peduncular article 1; lateral head lobe acute. Antenna 1 long, not pediform; length ratio of peduncular articles 1–3 as 1.00:0.57:0.24; flagellum long, 1.13 times as long as peduncle, articles 1, 2, 3, 4, 6, 8, 10 with a few aesthetascs for each. Antenna 2: peduncular article 5 slightly shorter than article 4, articles 1–3 combined shorter than article 4; article 4 with short posterodistal cusp. Upper lip: unknown. Lower lip: outer lobes horizontal. Mandible: molar weakly tuberculate, smooth; incisor with 9 teeth; left lacinia 9-dentate, right lacinia absent; palp large, length ratio of articles 1–3 as 1.0:2.5:3.4; inner margin of palp article 3 lined with 8 strong pectinate D-setae, apex with 3 long and 1 short E-setae, A-seta absent, medial surface covered with numerous setules; article 2 with 8 setae along distal half of inner margin; article 1 without setae. Maxilla 1: inner plate with single club-shaped plumose apical seta; apex of palp obliquely rounded, with row of 8 spine-like setae ( Watling 1989: type IIA3). Maxilla 2: inner plate subequal in length to and broader than outer plate; inner margin in the middle with single strong plumose seta. Maxilliped: inner plate short, not reaching proximal margin of palp article 1, apex subrounded, with 3 short setae and 6 button-shaped setae; outer plate short, reaching about 2/3 length of palp article 2, apex truncate, 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 1.0:1.1:1.3:1.3, inner margin of article 3 with numerous setae and covered with submarginal field of numerous setules; article 4 slender, slightly curved inside, with dense row of 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 3–4 small teeth. Coxal plates 2–3 deep, ventral margins subrounded, posteroventrally with 3 small teeth; coxal plate 4 broader, deeply excavate in proximal 1/3 posteriorly; 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, largest in pereopod 4, sac-like.

Pereopod 1 (gnathopod 1): basis, anterior margin setose, posterior margin weakly expanded, with row of setae; ischium short, with posterodistal seta; merus, distal margin with row of setae, posterior margin with 3 groups of setae; carpus 2.2 times as long as wide, with 2 setae along anterior margin, posterior margin with 2–3 groups of plumose setae, with dense row of plumose setae and with 2 stout comb setae posterodistally, medial surface with 3 transverse groups of setae along posterior margin; propodus slightly narrowed distally, 0.92 times as long as carpus, 2.2 times as long as wide, posterior margin with 4 spine-like setae near palmar angle, medial surface with 3 transverse groups of setae along anterior margin, palm oblique, roundly passing to posterior margin; dactylus subequal to palm in length, 0.4 times as long as propodus. Pereopod 2 (gnathopod 2): basis, anterior and posterior margins setose; ischium short, with posterodistal seta; merus with row of simple setae sparsely scattered along distal margin, with 2 groups of long setae along posterior margin; carpus long and narrow, 2.7 times as long as wide, posterior margin with 4 groups of long setae, posterodistally with dense row of long setae and 2 stout comb setae; propodus slightly narrowed distally, 0.8 times as long as carpus, 2.5 times as long as wide, posterior margin with 4 spine-like setae near palmar angle, medial surface with 3 groups of setae along anterior margin and with row of 4 short setae parallel to posterior margin, palm oblique, roundly passing to posterior margin; dactylus short, slightly overhanging palm, 0.38 times as long as propodus.

Pereopods 3–4 similar, length ratio from basis to dactylus 1.00:0.34:0.70:0.49:0.67:0.25; basis sublinear, anterior and posterior margins densely setose; merus anterodistally produced to 1/4 of carpus length; posterior margin of carpus with 12 (pereopod 3) and 21 (pereopod 4) short spine-like setae; posterior margin of propodus with 23 (pereopod 3)—24 (pereopod 4) short spine-like setae; dactylus medium wide, 0.36–0.39 times as long as propodus. Pereopods 5–7 closely homopodous, length ratio from basis to dactylus 1.00:0.24:0.68–0.80:0.50–0.58:0.75:0.30; basis posterodistally truncate; merus posterodistally produced to 2/5–1/2 of carpus length, acute, anterior margin with 10–14 short spine-like setae; carpus, anterior margin with 18–23 short spine-like setae; propodus 4.1 times as long as wide, anterior margin with 33 (pereopod 5) and 22 (pereopod 6) short spine-like setae; dactylus medium wide.

Epimeral plates 1–3: ventral margin with 3 (plates 1 and 2) and 5 (plate 3) short spine-like setae, posteroventral corners acute, posterior margins without serration. Pleopods regular, basal article of inner ramus with 4 stout two-pointed plumose setae (coupling setae) along inner margin; outer ramus with 16 (pleopod 1), 14 (pleopod 2) and 13 (pleopod 3) articles, inner ramus with 13 (pleopods 1 and 2) and 12 (pleopod 3) articles.

Uropod 1: peduncle about as long as inner ramus; outer ramus 0.94 times as long as inner ramus; margins of peduncle and rami with serially-arranged numerous short spine-like setae. Uropod 2: inner ramus 1.6 times as long as peduncle, outer ramus 0.8 times as long as inner. Uropod 3: inner ramus 2.4 times as long as peduncle, with row of 7–8 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 and medial margins for each, with acute and non-spinose apex. Telson linguiform, with ventral keel, dorsal surface with 2 penicillate setae in distal half and 2 oblique rows of microscopic setules in proximal half.

Female unknown.

Type locality. Sea of Japan, Strait of Tartary, shelf of western Sakhalin Island, (47°02'50"N 142°02'35"E, 10 m) GoogleMaps .

Etymology. Named from Latin “longum antennae” (long antenna) according to the structural features of antenna 1 and antenna 2.

Ecology. Dactylopleustes longoantennis sp. nov. was found on rocks in the depth of 10 m, commensal on sea urchin Strongylocentrotus intermedius .

Distribution. Known only from the type locality.

Remarks. Dactylopleustes longoantennis sp. nov. is morphologically close to the species group with long plesiomorphic antennae 1 and 2: D. tzvetkovae sp. nov. and D. yoshimurai . Dactylopleustes longoantennis sp. nov. differs from D. tzvetkovae sp. nov. and D. yoshimurai by the flagellum of antenna 1 consisting of 18 articles (11–12 or fewer articles in other species), and the apex of maxilliped outer plate with 3 heavy apical setae (with 1–2 heavy and 1 small apical setae in other species).