Quasimelita jarettii, Labay, Vjacheslav S., 2014

Labay, Vjacheslav S., 2014, Review of amphipods of the Melita group (Amphipoda: Melitidae) from the coastal waters of Sakhalin Island (Far East of Russia). II. Genera Quasimelita Jarrett & Bousfield, 1996 and Melitoides Gurjanova, 1934, Zootaxa 3869 (3), pp. 237-280 : 250-259

Quasimelita jarettii sp. nov.

Figures 1 , 9–15 , 30 b

Diagnosis. Pleon segments without dorsal armament. Urosome segment 1 with central large tooth; urosome 2 with 2 short teeth and 2 cuspidate seta. Anterior head lobe large, rounded, lower margin smooth. Eye small, round. Coxa 1 with rounded anterior corner; margins of all coxae without distinct serrations. Lower edges of coxal plates 1–4 in a straight line. Propodus of pereopod 1 (male) relatively small, shorter than carpus, not broad distally, palm slightly oblique, smooth palm that is armed distally with numerous closely set small cuspidate setae. Pereopod 2 (male), anterior margin of dactyl strongly setose; palm oblique, stepwise, with stout simple setae on ledges and along the palmar margin. Maxilla 1, inner plate with 6–8 marginal setae; palp segment 1 with 6–10 lateral setae. Maxilla 2, facial setae of inner plate very reduced (4–5 setae), distally medial, closely submarginal. Uropod 3 very long, proximal segment of outer ramous slender, tapering distally, with 4–6 clusters of marginal stout simple setae; terminal segment distinct, length as 0.1–0.12 of proximal segment. Telson lobes with rounded or obtuse tips.

Type material. Holotype male, 12 mm, 41802/Cr-1507, Chikhacheva Bay, Tatar Strait, Japan Sea, Far East of Russia (51°27'80''N 140°54'28''E, 26 m), silt, M.G. Rogotnev & P.V. Polupanov, 19 August 2009. Paratypes: 1 female, 10 mm, 41803/Cr-1508; 4 males and 7 female 41804/Cr-1509 with same data as holotype.

Type locality. Chikhacheva Bay, the northern part of Tatar Strait, Japan Sea, Far East of Russia (51°27'N 140°54'E, 17–30 m).

Description. Male (12 mm). Vital body color is grey-olive. Thoracic segments smooth dorsally ( Fig. 9 a, b). Pleon segments without teeth. Urosome segment 1 with large central tooth; urosome 2 with pair of short teeth and two simple cuspidate seta. Body surface with rare specific sensible setae: ( Fig. 12 e) from the top of the stalk tillering diverge few simple long branches.

Head: ( Fig. 9 c) slightly shorter than pereonites 1 and 2 together, with an indistinct rostrum; eyes small round; anterior head lobe large rounded; lower margin with a short notch.

Antenna 1: ( Fig. 9 d) nearly 40% of body length, slender; flagellum exceeding 1.1 times the length of the peduncle, bearing 20 articles, few very thin and short setae scattered along flagellum; peduncle article 1 double width but slightly shorter length to article 2, with 2 stout simple setae along distal half of posterior margin, article 3 0.29 times the length of article 2; accessory flagellum 3–4-articulate.

Antenna 2: ( Fig. 9 e) flagellum almost 0.33 times as long as peduncle, 9 articles, with few thin setae on each article; peduncle articles 5 slightly shorter than article 4, articles 1, 2, 3 together shorter than article 4 or article 5 each; article 1 with protruding lobe reaching the middle of the article 3; articles 4 and 5 with numerous evenly spaced tufts of thin setae.

Mouthparts.

Labrum: ( Fig. 9 f) frontal margin slightly concave medially, densely covered by minute setae.

Mandible: ( Fig. 10 a–f) incisor crenulate and stretching in a rounded tip; raker setae stout subplumose, numerous (8+), equal to incisor in length; molar flattened triturative; palp 3-articulate, palp segment 2 distally rarely setose, palp segment 3 setose, 1-st article with protruding lobe, the percentage of total length of the articles of the palp 16% (article 1), 45% (article 2) and 39% (article 3).

Labium: ( Fig. 10 g) inner lobes small but well defined, rounded; outer lobes semi-square / rounded at distal margin.

Maxilla 1: ( Fig. 10 h) inner plate suboval, lined with a row of simple setae (5–6 setae), with two plumose setae apically; outer plate elongate, 1.7–1.8 times as long as inner plate, apically with 2 rows of 9 bifurcate and comblike strong setae; palp 2-articulate, article 2 1.6 times as long as article 1, article 2 apical margin with two rows of 9–10 simple setae each.

Maxilla 2: ( Fig. 10 i) inner plate slightly shorter than outer plate, facial setae of inner plate reduced (4–5), distal, closely submarginal, tip covered with numerous simple setae; outer plate with numerous simple setae on the tip, subapically with a rare row of 9–10 setae.

Maxilliped: ( Fig. 11 a) compact; inner plates large, fully cleft, distal margin with a row of 3 teeth, inner margin with long plumose setae (8–10 setae); outer plates almost reaching distal margin 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 plumose setae, with several transverse bundles of short setae; palp 4-articulate, the percentage of total length of the articles of the palp are 17% (article 1), 45% (article 2), 21% (article 3), 17 (article 4), article 2 with numerouse setae along distal part of inner margine; tip of article 3 bilobed with a row of long simple setae; article 4 inner margin with a line of serrate setae (Watling type IV.1) ( Watling 1989).

Pereopod 1 (gnathopod 1): ( Fig. 11 b) coxa extended distally, with rounded anterior corner; basis straight with a tuft of simple setae at the proximal part of anterior margin and with rare long setae along posterior margin; merus subrectangular, with a row of simple setae along distal margin and with a spot of short setae at the posterior margin; carpus long, 1.25 times as long as propodus, 9–10 oblique rows of long serrate 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, slightly broadest distally, with numerous groups of long serrate setae along outer posterior margin, with 5 rare tufts of long simple setae along anterior margin and with a dense bunch of long simple setae at the anterior distal corner, palm slightly oblique and minutely serrate with a dense row of numerous short stout simple setae, outer surface with two transverse rows of long setae distally; dactylus as long as palm, with nail and with tooth-like protrusion as long as nail above it.

Pereopod 2 (gnathopod 2): ( Fig. 11 c, d) coxa rounded, slightly narrowing distally, gills with indistinct peduncle; basis slightly expands medially, longer than coxa, with a few long simple setae along posterior margin and with numerous long setae along distal part of anterior margin; merus subrectangular with small acute protrusion at the posterior distal corner, with a few long setae along posterior margin; carpus triangular, 2.3 times shorter than propodus; propodus suboval, palm oblique, stepwise, with stout simple setae and a tuft of long setae on ledges and along the palmar margin, anterior margin lined with several groups of setae, posterior margin with numerous tufts of serrate setae; dactylus as long as oblique part of palm, slightly curved to the inside of propodus, inner margin with a rare row of short simple setae, outer margin strongly setose, tip of dactylus with acute nail.

Pereopod 3: ( Fig. 11 e) coxa similar size as coxa 2, rounded distally; basis linear with few minute setae along anterior margin and with rare long simple setae along posterior margin; merus long with 2 strong simple setae along anterior margin and with a single cluster from one strong simple seta and few small setae at the anterior distal corner, posterior margin with few thin setae; carpus 0.75 as long as merus, with 5 bunches of strong simple setae along posterior margin; propodus linear, more narrow and as long as carpus, with 4 bunches of strong simple setae along posterior margin; dactylus medium (0.4 times length of propodus), with nail.

Pereopod 4: ( Fig. 12 a) coxa subequal in size to coxa 3, subquadrate, anterior and posterior corners rounded, posteriorly slightly excavated; segements 2–7 similar to that of pereopod 3.

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

Pereopod 5: ( Fig. 12 b) coxa with slightly rounded front margin, with quadrate hind margin and with subqadrate anterior lobe pulled back and down; basis regular, with posterior wing, width 0.66 times as long, posterior distal corner rounded, hind margin crenulated, anterior margin with small stout setae; ischium subquadratic; merus slightly broaded medially, with two short stout setae at the middle of posterior margin, with two strong stout setae at the posterior distal corner; carpus 0.73 times as long as merus, with 2 groups of 2 strong 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 1.3 times as long as carpus, with 5–6 bunches of strong simple setae along anterior margin; dactylus small (0.3 times length of propodus), with nail.

Pereopod 6: ( Fig. 12 c) coxa with quadrate hind margin and with anterior lobe pulled back and down, front margin with few stout cuspidate setae; basis regular, with posterior wing, slightly narrowed distally, width 0.66 times as long, posterior distal corner slightly rounded, hind margin crenulated, anterior margin with small stout setae; ischium subquadratic; merus long, with 2 short stout simple setae along posterior margin and with few thin simple setae along anterior margin, and with clusters of 2–3 strong stout setae at anterior and posterior distal corners each; carpus 0.77 times as long as merus, with 3 groups of 1–3 strong stout setae at the anterior margin and with a single clusters of strong stout setae at the anterior and posterior distal corners each; propodus linear, more narrow and 1.2 times as long as carpus, with 4 clusters of strong simple setae along anterior margin; dactylus small (0.3 times length of propodus), with nail.

Pereopod 7: ( Fig. 12 d) coxa small, without distinct anterior lobe and with rounded posterior lobe; basis regular, with posterior wing, narrowed distally, width 0.62 times length, posterior distal corner acute, hind margin crenulated, anterior margin with small setae; ischium subquadratic; merus long, with 3 stout simple setae along anterior and posterior margins, and with single clusters of 2–3 strong stout 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 smaller than gill 5.

Epimeral plates: ( Fig. 13 a, b, c) hind corner acuminate; plate 1 subquadrate, posterior margin with 2–3 indistinct notches, lower margin with 3 strong simple setae, hind corner slightly produced with small tooth; plate 2 posterior and ventral margins convex, with oblique crest, posterior margin with 2–3 indistinct notches, ventral margin with a row 5–6 strong simple setae; plate 3 hind corner produced, acute, posterior margin concave, ventral margin with a row of 10 strong simple setae.

Pleopods: ( Fig. 13 d–h) normal, no sexual dimorphism; peduncle with two specific toothed coupling setae on the inner corner; inner ramus longer than outer ramus, coupling basis of inner ramus with 3–7 of specific stout twopointed plumose setae along inner margin: pleopod 1 (7), pleopod 2 (5), pleopod 3 (3).

Uropod 1: ( Fig. 13 i) peduncle with strong and curved interramal spur; rami subequal in length, 0.8–0.85 as long as peduncle; peduncle and rami with tiny simple setae along outer edge, both rami with few tiny simple setae at tip.

Uropod 2: ( Fig. 13 j) peduncle shorter than outer ramus (0.8 ramus length); inner ramus shorter than outer, with numerous simple cuspidate setae along outer margin; uropod 2 shorter than uropod 1.

Uropod 3: ( Fig. 13 k) very long, being bent back reaches the middle of the second pleon segment, 1.4 times as long as uropod 1; peduncle shorter than peduncle of uropod 1, with two cuspidate setae along anterior margin, with two clusters of simple cuspidate setae at the apex; elongate 2-articulate outer ramus (8 times length of inner ramus) 3.3 times as long as peduncle, with 7 tufts of small simple stout setae along the anterior margin and with 5 tufts of small simple stout setae along the posterior margin of article 1, article 2 minute, more than 10 times shorter than article 1; inner ramous short and ovoid with two various cuspidate setae at the tip.

Telson: ( Fig. 13 l) fully cleft; lobes diverging distally, with rounded tips; proximal notch positioned laterally; apical and subapical simple cuspidate setae long.

Female (10 mm). Similar to male. Vital body color grey-olive. Thoracic and pleon segments smooth dorsally, without teeth and humps ( Fig. 14 a). Urosome segment 1 with large central tooth; urosome 2 dorsally with 2 teeth and single cuspidate seta each.

Antenna 1: similar to as in male, 49% of body length, slender; flagellum exceeding 1.2 times the length of the peduncle, 21 articles, few very thin and short setae scattered along flagellum; peduncle article 1 twice as wide but slightly shorter than article 2; article 3 0.29 times as long as article 2; accessory flagellum 4-articulate.

Pereopod 2 (gnathopod 2): ( Fig. 14 d, e) with sexual dimorphism; coxa rounded subquadrate; basis straight, longer than coxa, with a few long simple setae along posterior margin and with numerous long setae along distal part of anterior margin; merus subrectangular, with acute protrusion at the posterior distal corner, with a row of setae along distal margin; carpus broadened distally, 1.7 times shorter than propodus, posterior lobe slightly produced with 7 clusters of serrate setae; propodus suboval, slightly narrowed distally, width 0.6 times length, palm oblique, convex, with two ledges in the anterior part, with rare stout simple setae along the palmar margin, posterior margin with numerous tufts of serrate setae, outer surface with numerous clustaers of short setae along posterior margin and with 4 rows of long setae along palmar margin; dactylus longer than oblique part of palm, slightly curved to the inside of propodus, outer margin strongly setose, tip of dactylus with acute nail.

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

Uropod 3: ( Fig. 15 d) long, but much shorter than the male, being bent back reaches the middle of the third pleon segment, 1.4 times as long as uropod 1; peduncle with two cuspidate setae along anterior margin, with two clusters of simple cuspidate setae at the apex; elongate 2-articulate outer ramus (8.5 times length of inner ramus) 2.9 times as long as peduncle, with 5 tufts of small simple stout setae along the anterior margin and with 3 tufts of small simple stout setae along the posterior margin of article 1, article 2 minute, almost 10 times shorter than article 1; inner ramous short and ovoid with two various cuspidate setae at the tip.

Sexual dimorphism: Only in structure of pereopod 2 and in the length of uropod 3. Pereopod 2 in male bigger than in female, carpus in male more shorter than in female. Uropod 3 in male more longer than in female.

Variations: Telson lobes may be with rounded or obtuse tips.

Etymology. Named in honor of Canadian scientist Norma E. Jarrett who contributed very broadly to the knowledge of melitid amphopods.

Ecology. Q. jarettii was found between 15–30 m on silt-sand and silt bottoms. Females with the beginnings of oostegites were detected in the type locality in August.

Distribution. The northern part of Japan Sea, Chikhacheva Bay ( Fig. 1 ).

Remarks. Quasimelita jarettii sp. nov. is most similar to Q. quadrispinosa in description of Vosseler (Vosseler, 1889). Q. jarettii differs from Q. quadrispinosa in the structure of uropod 3. Q. quadrispinosa have a long peduncle of uropod 3 (slightly shorter than outer ramous); peduncle of uropod 3 in Q. jarettii very short.

Q. jarettii differs from Q. quadrispinosa ( Amphipoda from the West Spitsbergen fjords) in the shape of pereopod 7 basis also. In Q. quadrispinosa the basal segment of pereopod 7 expanded medial-distally; in Q. jarettii the basal segment of pereopod 7 expanded proximally.

Figures

FIGURE 1. Distribution of Quasimelita species on the shelf of Sakhalin Island and nearest area.

FIGURE 9. Quasimelita jarettii sp. nov., holotype, male: a—lateral view, b—carination of abdominal segments, c—cephalon, d—antenna 1, e—antenna 2, f—upper lip; scale: a, d, e— 1 mm; b— 0.5 mm, c— 0.2 mm.

FIGURE 10. Quasimelita jarettii sp. nov., holotype, male: a, b, c—left mandible, d, e, f—right mandible, g—lower lips, h — maxilla 1, i—maxilla 2; scale: a, d— 0.2 mm; g, h, i— 0.1 mm.

FIGURE 11. Quasimelita jarettii sp. nov., holotype, male: a—maxilliped, b—pereopod 1, c—pereopod 2, d—dactylus and palmar margin of pereopod 2, inner side, e—pereopod 3; scale: a— 0.1 mm; b, c, e— 1 mm.

FIGURE 12. Quasimelita jarettii sp. nov., holotype, male: a—pereopod 4, b—pereopod 5, c—pereopod 6, d—pereopod 7, e—sensible seta from body surface; scale: a, b, c, d— 1 mm.

FIGURE 13. Quasimelita jarettii sp. nov., holotype, male: a—epimer 1, b—epimer 2, с—epimer 3, d—pleopod 2, e—coupling spines of pleopod 2, f, g, h—coupling setae of pleopods 1, 2 and 3, i—uropod 1, j—uropod 2, k—uropod 3, l—telson; scale: a, b, c— 0.2 mm; d, i, j, k, l— 1 mm; e – h— 0.1 mm.

FIGURE 14. Quasimelita jarettii sp. nov., paratype, female: a—carination of abdominal segments, b—pereopod 1, c—dactylus and propodus of pereopod 1, outer side, d—pereopod 2, e—dactylus and palmar margin of pereopod 2; scale: a, b, d— 1 mm.

FIGURE 15. Quasimelita jarettii sp. nov., paratype, female: a—epimer 1, b—epimer 2, с—epimer 3, d—uropod 3, e—telson; scale: a – d— 1 mm; e— 0.1 mm.

FIGURE 30. Dorsal carination of new species of genera Quasimelita and Melitoides: a— Quasimelita tolyza sp. nov., male, shelf of north-eastern Sakhalin, b— Quasimelita jarettii sp. nov., male, Chikhacheva Bay, Japan Sea, c— Quasimelita serraticoxae sp. nov., male, shelf of north-eastern Sakhalin, d— Quasimelita serraticoxae sp. nov., male, Kashevarova shoal, e— Melitoides kawaii sp. nov., male, shelf of north-eastern Sakhalin; scale: 1 mm.