Abludomelita okhotensis, Labay, Vjacheslav S., 2016

Labay, Vjacheslav S., 2016, Review of amphipods of the Melita group (Amphipoda: Melitidae) from the coastal waters of Sakhalin Island (Far East of Russia). III. Genera Abludomelita Karaman, 1981 and Melita Leach, 1814, Zootaxa 4156 (1), pp. 1-73 : 39-46

Abludomelita okhotensis sp. nov.

Figures 2 , 16–20 , 28 d

Diagnosis. Pleon segments 1–2 with central tooth and 2–3 lateral teeth on each side; pleon segment 3 with central tooth and 3 lateral teeth on each side; cental dorsal tooth of all pleon segments is small, shorter than neigbour teeth. Urosome segment 1 with central tooth and with 2 lateral teeth on each side; urosome 2 with 2 pairs of acute teeth and with strong seta in each lateral pair. Anterior head lobe shallow, rounded, lower margin with prominent accessory process. Maxilla 1, palp segment 1 with 2 lateral setae. Maxilla 2, inner plate, facial setae developed, submarginal in position. Pereopod 1 (male) long suboval, palm rounded, without distinct palmar angle. Pereopod 2 (male), dactylus inflated, with obtuse tip, anterior margin of dactylus rarely setose; palm oblique, with low irregular teeth in the anterior half and with a produced postero-distal tooth. Telson lobes, subapical notches equal removed from the base.

Type material. Holotype male, 8.3 mm, X 44093 /Cr-1668, Sea of Okhotsk, Kashevarova shoal (56°49'44" N, 143°26'34" E, 109 m), stones, gravel and pebble, V.Iu. Lalov, 13 August 2013.

Type locality. Sea of Okhotsk (56°49'44" N, 143°26'34" E, 109 m)

Description. Male (8.3 mm). Small size species. Vital body color is light-brown. Thoracic segments smooth dorsally ( Fig. 16 , 17 a, 28d). Pleon segments 1–2 with small central tooth and 3 (rarely 2) lateral teeth on each side, submedial teeth is larger; pleon segment 3 with the posterior row of 7 teeth, central tooth small, marginal teeth are larger than the intermediate in the each lateral group of teeth. Urosome segment 1 with central tooth and with 2 lateral teeth on each side (1 large tooth and 1 small denticle); urosome 2 with 2 lateral pairs of acute teeth and with the stout cuspidate seta in the each pair.

Head: ( Fig. 17 b) subequal to pereonites 1 and 2 together, with an indistinct rostrum; eyes small suboval; anterior head lobe rounded; lower margin with a short notch.

Antenna 1: ( Fig. 17 c) nearly 84% of body length, slender; flagellum exceeding 1.2 times the length of the peduncle, bearing 37 articles, few very thin and short setae scattered along flagellum; peduncle article 1 subegual to article 2 length, with 6 stout simple setae along posterior margin and with short acute protrusion at the distal posterior margin, article 3 0.39 times as long as article 2; accessory flagellum 6-articulate.

Antenna 2: ( Fig. 17 d) flagellum almost 0.48 times as long as peduncle, 13 articles, with a crown of few thin setae on each article; peduncle articles 5 0.83 times as long as article 4, articles 1, 2, 3 together 1.3 times shorter than article 4; article 2 with protruding lobe reaching the distal end of article 3; articles 4 and 5 with numerous evenly spaced tufts of thin setae.

Mouthparts. Labrum: ( Fig. 17 e) frontal margin slightly concave medially, laterally pubescent.

Mandible: ( Fig. 17 f, g) incisor crenulate and stretching in a rounded tip; raker setae stout serrated, numerous (13–14), subequal to incisor in length; molar flattened triturative; palp 3-articulate, palp segment 2 with 6–7 rare setae along posterior margin, palp segment 3 with 9–11 setae, distal setae are larger, 1-st article with protruding lobe, the percentage of total length of the articles of the palp 18% (article 1), 35–41% (article 2) and 41–47% (article 3).

Labium: ( Fig. 17 h) inner lobes small but well defined, rounded; outer lobes rounded, with minute setae at tips.

Maxilla 1: ( Fig. 17 i) inner plate triangulate, lined with a row of 11setae; outer plate elongate , 1.7 times as long as inner plate, apically with 2 rows of 9 bifurcate strong setae; palp 2-articulate, article 2 2.2 times as long as article 1, article 2 apical margin with two rows of 9–10 simple setae each.

Maxilla 2: ( Fig. 17 j) inner plate slightly shorter than outer plate, facial setae of inner plate numerous, located submarginally, tip covered with numerous simple setae; outer plate with numerous simple setae on the tip.

Maxilliped: ( Fig. 18 a) inner plates medium size, fully cleft, distal margin with a row of 3 teeth, inner margin with long plumose setae (9–11 setae); outer plates reaching 4/5 length of palp article 2, inner margin lined with a row of short stout teethlike setae longer toward the apex, smoothly into the apical row of long thin setae, with several transverse bundles of short setae submarginally; palp 4-articulate, the percentage of total length of the articles of the palp are 14% (article 1), 33% (article 2), 25% (article 3), 28 (article 4), article 2 with numerouse setae along inner margine; tip of article 3 with a crown of long simple setae; article 4 inner margin with a line of simple setae.

Pereopod 1 (gnathopod 1): ( Fig. 18 b, c) coxa extended distally, with rounded anterior corner; basis straight with a row of short simple setae along anterior margin and with rare long setae along posterior margin; ischium with dense tuft of long setae at the postero-distal corner; merus subrectangular, with a crown of simple setae along distal margin and with a long spot of dense short setae at the posterior margin; carpus 1.2 times as long as propodus, 8–9 oblique rows of long setae along outer posterior margin, with a row of long setae along anterior part of distal margin and tomentose at the anterior-distal corner; propodus suboval, with few groups of long setae along posterior margin, with 5 tufts of long simple setae along anterior margin and with a dense bunch of long simple setae at the anterior distal corner, palm oblique rounded, smoothly passes in posterior margin, minutely serrate with a row of numerous short stout simple setae, outer surface with a transverse row of long setae distally; dactylus as long as palm, curved near the tip, with nail and with short tooth-like protrusion above it.

Pereopod 2 (gnathopod 2): ( Fig. 18 d, e) coxa extended, rounded distally, with acute teeth at the posterior distal corner; gills with indistinct peduncle; basis slightly expands medially, as long as coxa, with a row of short setae along anterior margin and with a few long simple setae along posterior margin; merus subrectangular with long acute protrusion at the posterior distal corner, without setae along posterior margin; carpus triangular, 4 times shorter than propodus; propodus extends distally, palm oblique, with 3 slight protuberances at the proximal half, palmar corner with large acute tooth, posterior margin with numerous tufts of setae, inner surface with a fosse and two short stout setae near the palmar corner; dactylus slightly inflated in the middle part, slightly shorter than palm, slightly curved to the inside of propodus, outer margin with a few short setae, tip of dactylus obtuse.

Pereopod 3: ( Fig. 19 a) coxa long, subequal to coxa 2, with parallel anterior and posterior margins, rounded distally; basis linear, slightly curved in the proximal 1/5, with rare minute setae along anterior and posterior margins; merus long, with 3 groups of strong simple setae along anterior margin and with a single cluster of simple setae at the anterior distal corner, posterior margin with 4 tufts of simple setae, posterior distal corner with a bunch of simple setae; carpus 0.79 times as long as merus, with 6 groups of strong simple setae along posterior margin; propodus linear, as long as carpus, with 6 groups of short strong simple setae along posterior margin; dactylus small (0.3 times length of propodus), with nail.

Pereopod 4: ( Fig. 19 b) coxa shorter than coxa 3, anterior and posterior corners rounded, posteriorly excavated; segements 3–7 shorter than in pereopod 3; merus with two groups of strong simple setae along anterior margin; carpus with 5 groups of strong simple setae along posterior margin; propodus with 6 groups of short strong simple setae along posterior margin; dactylus medium (0.36 times length of propodus), with nail.

Pereopods 5–7 elongated from pereopod 5 to pereopod 6, pereopods 6 and 7 equal in length.

Pereopod 5: ( Fig. 19 c, d) coxa with rounded front margin, with sloped hind margin, with rounded posterior distal corner and with rounded anterior lobe pulled down; basis regular, with narrow posterior wing, width 0.61 times as long, posterior distal corner rounded, hind margin crenulated, anterior margin with small stout setae; merus slightly broaded medially, with 3 short stout setae along anterior margin, with 2 short stout setae at the middle of posterior margin, with a cluster of stout setae at anterior and posterior distal corners each; carpus 0.93 times as long as merus, with 2 groups of 2 strong setae at the anterior margin and with a single cluster of strong stout setae at the anterior and posterior distal corners each; propodus linear, more narrow and 1.45 times as long as carpus, with 6 bunches of strong simple setae along anterior margin; dactylus medium (0.36 times length of propodus), with nail.

Pereopod 6: ( Fig. 19 e, f) coxa with sloped hind margin, posterior distal corner distinct, with acute anterior lobe pulled back and down, front margin with few short simple setae; basis regular, slightly narrowed distally, with posterior wing, width 0.59 times as long, posterior distal corner slightly rounded, hind margin crenulated, anterior margin with small stout setae; merus long, with 3–4 short stout simple setae along anterior and posterior margins each, and with cluster of strong stout setae at anterior and posterior distal corners each; carpus 0.88 times as long as merus, with 2 groups of 2 stout setae at the anterior margin and with a single cluster of strong stout setae at the anterior and posterior distal corners each; propodus linear, more narrow and 1.4 times as long as carpus, with 6 clusters of short cuspidate setae along anterior margin; dactylus medium (0.36 times length of propodus), with nail.

Pereopod 7: ( Fig. 19 g, h) coxa small, without distinct anterior lobe and with rounded posterior lobe; basis regular, with rounded posterior wing, width 0.64 times of length, posterior distal corner rounded, posterior margin crenulated, anterior margin with small stout setae; merus long, with 3 groups of stout setae along anterior margin, with two tufts of stout setae along posterior margin, and with single cluster of strong setae at anterior and posterior distal corners each; carpus, propodus and dactylus similar to that in pereopod 6.

Coxal gills 2–6. Coxal gill 6 slightly smaller than gill 5.

Epimeral plates: ( Fig. 20 a, b, c) plate 1 with oblique crest, posterior margin slightly rounded, with 1 unclear notch, lower margin without armaments, hind corner subquadrate; plate 2 posterior margin slightly concave, ventral margins convex, with oblique crest, posterior margin with 2 indistinct notches, ventral margin without armaments; plate 3 hind corner produced, acute, posterior margin concave, with 3 acute teeth, ventral margin with a row of 5–6 strong simple setae.

Pleopods: ( Fig. 20 d–h) normal; peduncle with two specific toothed coupling setae on the inner corner; coupling basis of inner ramus with 3 specific stout two-pointed cuspidate setae along inner margin.

Uropod 1: ( Fig. 20 i) peduncle with strong interramal spur; rami subequal in length, 0.9–0.91 as long as peduncle; peduncle and rami with tiny simple setae along margins, both rami with few tiny simple setae at the tip.

Uropod 2: ( Fig. 20 j) peduncle shorter than outer ramus (0.76 ramus length), with acute protrusion at the distal margin; inner ramus shorter than outer, with numerous simple tiny setae along outer margin; uropod 2 shorter than uropod 1.

Uropod 3 is lost.

Telson: ( Fig. 20 k) fully cleft; lobes diverging distally, proximal notch positioned medially; apical and subapical simple cuspidate setae long, lobes with single short cuspidate setae at the medial margin each.

Females unknown.

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

Ecology: A. okhotensis was found in the depth 109 m on the stones, gravel and pebble bottom in the layer of constant low temperature (-1.2—+0.5°C).

Distribution: Only type locality. Sea of Okhotsk near the Kashevarova shoal ( Fig. 2 ).

Remarks. Abludomelita okhotensis sp. nov. is identical to Abludomelita rotundactyla ( Ren, 2012) by the scheme of dorsal carination of abdomen. A. okhotensis differs from A. rotundactyla by the structure of pereopod 2 of male: in A. okhotensis palm of propodus oblique, with 3 slight protuberances at the proximal half, palmar corner with large acute tooth, dactylus slightly inflated in the middle part; in A. rotundactyla propodus very inflated, palm oblique, with 2 strong protuberances at the proximal half; palmar corner with truncated tooth, dactylus heavy, as long as palmar margin, extended distally.

Figures

FIGURE 2. Distribution of Abludomelita species on the shelf of Sakhalin Island and nearest area.

FIGURE 16. Abludomelita okhotensis sp. n., holotype, male: lateral view without uropod 3; scale— 2 mm.

FIGURE 17. Abludomelita okhotensis sp. n., holotype, male: a—carination of abdominal segments, b—cephalon, c—antenna 1, d—antenna 2, e—upper lip, f—left mandible, g—right mandible, h—low lips, i—maxilla 1, j—maxilla 2; scale: b, c, d, e, h— 1 mm; f, g, i, j— 0.1 mm.

FIGURE 18. Abludomelita okhotensis sp. n., holotype, male: a—maxilliped, b—pereopod 1, c—inner side of propodus and dactylus of pereopod 1, d—pereopod 2, e—inner side of palmar margin of pereopod 2; scale: a— 0.1 mm; b – e— 1 mm.

FIGURE 19. Abludomelita okhotensis sp. n., holotype, male: a—pereopod 3, b—pereopod 4, c—coxa 5 without coxal gill, d—pereopod 5, e—coxa 6, f—pereopod 6, g—coxa 7, h—pereopod 7; scale— 1 mm.

FIGURE 20. Abludomelita okhotensis sp. n., holotype, male: a—epimer 1, b—epimer 2, c—epimer 3, d—pleopod 2, ecoupling spines of pleopod 2, f—coupling setae of pleopod 1, g—coupling setae of pleopod 2, h—coupling setae of pleopod 3, i—uropod 1, j—uropod 2, k—telson; scale: a, b, c, d, i, j, k— 1 mm; e, f, g, h— 0.1 mm.

FIGURE 28. Dorsal carination of new species and subspecies of genera Abludomelita and Melita: a— Abludomelita rotundactyla (Ren, 2012), paratype, male, b— Abludomelita klitinii sp. n., holotype, male (type locality), c— Abludomelita klitinii sp. n., paratype, male (Ptichje Lake), d— Abludomelita okhotensis sp. n., holotype, male, e— Melita shimizui sachalinensis ssp. n., paratype, female; scale— 1 mm.