Dactylopleustes longoantennis Labay, 2025, sp. nov.
Creators: name: Labay, Vjacheslav S.
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Amphipoda
Pleustidae
Dactylopleustes
Dactylopleustes longoantennis

description: Dactylopleustes longoantennis sp. nov.
Figures 1a, 2a, j, 3a, b, l, 4a, j, 5a, j, 6a, b, 7a, b, 8a, h, 14–18, 36
Type material. Holotype: male, 6.6 mm, Х 54606 /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.
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).
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).
description: Published as part of 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, pp. 201-253 in Zootaxa 5627 (2) on pages 220-227, DOI: 10.11646/zootaxa.5627.2.1, http://zenodo.org/record/15325903