Melita shimizui sakhalinensis, 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 : 51-60

Melita shimizui sakhalinensis ssp. nov.

Figures 22–27 , 28 e

Diagnosis. Head with minute rostrum, lateral cephalic lobes rounded, with noth; eyes medium in size, suboval.

Dorsal surface of pleon segments 1–3 smooth, without medial dorsal teeth. Urosome segment 1 smooth dorsally; urosome 2 with two short stout setae on each side of middorsal line. Telson lobes with subapical notches. Antenna 1: accessory flagellum very short, 1+ articulated. Maxilla 2, inner plate, facial setae row absent. Propodus of pereopod 1 (male) excavated at basal part of palmar margin, with a distinct protuberance at the middle; distal palmar margin is short, convex roundly. Dactylus of pereopod 1 (male) short, with a tri-lobed process on inner margin. Propodus of pereopod 2 (male) oval elongated, without clear palmar corner; palm oblique, serrate, slightly tuberculate. Anterior lobe of coxa 6 (female) very long, hooked, apical part distorted. Uropod 3: outer ramus 1- segmented, elongated, with 3–4 groups of stout setae along both lateral and median margins.

Type material. Holotype: male, 5.1 mm, X 44094 /Cr-1669, low part of estuary of Tzunay river (basin of Aniva Bay , Sea of Okhotsk) (46°45'32" N, 142°40'27" E), sands and silt, E.S. Korneev & P.V. Polupanov, August 2014 . Paratypes: 5 males, X 44095 /Cr-1670; 6 females, X 44096 /Cr-1671 with same data as holotype . Paratype: female, 4.5 mm, X 44097 /Cr-1672, low part of estuary of Susuja river (basin of Aniva Bay , Sea of Okhotsk) (46°45'07" N, 142°43'10" E), sands and silt, E.S. Korneev & P.V. Polupanov, August 2014 . Paratypes: 2 males, X 44098 /Cr-1673 with same data . Paratype: female, 4.8 mm, X 44099 /Cr-1674, the channel of the lagoon lake Ptichje , south-east Sakhalin, Far East of Russia (54T 697139, 5143045, plankton nets), V.S. Labay, 17 July 2012 .

Type locality. Estuary of Tzunay river (basin of Aniva Bay , Sea of Okhotsk) (46°45'32" N, 142°40'27" E).

Description. Male (5.1 mm). Small size species. Vital body color light-grey. Pereon segments 1–7 smooth dorsally, without teeth and humps. Dorsal surface of pleon segments 1–3 smooth, without medial dorsal teeth. Urosome segments 1 and 3 smooth dorsally; urosome 2 with two short stout setae on each side of middorsal line ( Fig. 22 a).

Head: ( Fig. 22 b) slightly longer than pereonite 1, with minute rostrum; eyes medium oval, anterior head lobe rounded, with notch.

Antenna 1: ( Fig. 22 c) slender; flagellum subequal to peduncle in length, 21–22 articles, with a bunch of thin setae along distal margin of each article; peduncle article 1 double width, but 1.1 times shorter than article 2, article 3 0.53 times as long as article 2; accessory flagellum small, 2-articulate.

Antenna 2: ( Fig. 22 d) flagellum almost 0.39 times as long as peduncle, 7+ articles, with rare groups of thin setae on each article; peduncle articles 5 0.87 times as long as article 4, articles 1 + 2 + 3 are 0.77 times as long as article 5 and 0.67 times as long as article 4, articles 2 with protruding lobe almost reaching the distal end of next article, articles 3 without protruding lobe, with stout cuspidate seta at the distal posterior corner, article 5 with numerous tufts of thin setae on the surface.

Mouthparts. Labrum: ( Fig. 22 e) short and rounded, frontal margin densely covered by minute setae.

Mandible: ( Fig. 22 f) incisor crenulate and stretching in a rounded tip; few raker setae (4+) stout subplumose, slightly shorter then incisor; molar cylindrical triturative, chewing plate striate; palp short, slightly longer than basis from proximal margin to a tip of incisor, 3-articulate, 1-st article without protruding lobe, the percentage of total length of the articles of the palp are 15% (article 1), 47% (article 2), 38% (article 3), article 2 with 5 thin setae, article 3 with 9–10 setae.

Labium: ( Fig. 22 g) inner lobes small, but well defined, rounded, with dense minute setae; outer lobes rounded at distal margin, with dense minute setae at the tip.

Maxilla 1: ( Fig. 22 h) inner plate with truncate distal end, lined with a row of 6 plumose setae; outer plate elongate , reaching the ½ of palp article 2 length, apically with 2 rows of 9 strong toothed setae; palp 2-articulate, article 2 3.4 times as long as article 1, article 2 apically with two rows of 8–10 cuspidate setae each.

Maxilla 2: ( Fig. 22 i) inner plate slightly shorter than outer plate, facial row of setae of inner plate absent, apical margin covered with numerous simple setae; outer plate with same numerous of simple setae on the tip.

Maxilliped: ( Fig. 23 a) compact; inner plates large, fully cleft, inner and distal margins with long plumose setae; outer plates almost reaching the end of palp article 2, inner margin lined with a row of short stout teeth-like setae longer toward the apex, smoothly into the apical row of long setae, and with 3 submarginal dense rows of simple setae; palp 4-articulate, the percentage of total length of the articles of the palp are 13% (article 1), 40% (article 2), 27% (article 3), 20 (article 4), article 2 with numerous setae along distal half of inner margin; article 3 bilobed, with a crown of setae at the distal margin; article 4 inner margin with a line of setae, inner surface with a dense row of tiny setae.

Pereopod 1: ( Fig. 23 b, c) coxa medium long, rounded distally; basis with a row of long simple setae along anterior margin, some long setae along middle part of posterior margin; ischium with a group of few simple setae at the posterior distal corner, without a cushion of tiny setae; merus subrectangular, with rounded posterior distal corner, with cushion of short setae along posterior margin, distal margin with a row of long setae; carpus long, 1.5 times as long as propodus, 5 oblique rows of long setae along outer posterior margin, with a row of long setae along anterior and posterior parts of distal margin and tomentose at the anterior distal corner; propodus elongate , with 3 groups of long setae along outer posterior margin, with 5 tufts of long simple setae at the anterior margin, excavated at basal part of palmar margin, with a distinct protuberance at the middle; distal palmar margin is short, convex roundly, with two rows of bifurcated short stout setae; dactylus short, bulged basally, with a tri-lobed process on inner margin, with apical nail.

Pereopod 2: ( Fig. 23 d) coxa rectangular, subrounded distally; basis longer than coxa, with a few long simple setae along middle part of posterior margin and with rare setae along distal part of anterior margin; ischium tomentose near the posterior distal corner; merus subrectangular with short subacute protrusion at the posterior distal corner; carpus short, cup-shaped, almost 2.3 times shorter than propodus, with 6 tufts of long setae along posterior margin; propodus oval elongated, without clear palmar corner; palm oblique, serrate, slightly tuberculate, palmar margin with rare setae and with two rows of short spine-like setae, and a stout corner setae; tip of dactylus with nail, inner margin with few weak protuberances.

Pereopod 3: ( Fig. 24 a) coxa similar size as coxa 2, medium length, rounded distally; basis not extended, recurved, with long setae along anterior and posterior margins; merus slightly extended medially, with 3 strong cuspidate setae along anterior margin and with a stout simple seta at the anterior distal corner, posterior margin with few simple setae; carpus 0.69 times as long as merus, with 4 tufts of thin setae along posterior margin; propodus linear, more narrow and 1.2 times as long as carpus, with 4 tufts of thin setae along posterior margin; dactylus medium size (0.4 of propodus length).

Pereopod 4: ( Fig. 24 b) coxa as long as coxa 3, subquadrate, with rounded anterior and posterior distal corners, posteriorly excavated; leg is similar to that of the pereopod 3.

Pereopod 5 subequal to pereopod 6, pereopods 6–7 elongated from pereopod 6 to pereopod 7.

Pereopod 5: ( Fig. 24 c, d) coxa with rounded front margin and with anterior lobe pulled down, hind margin with rounded lower corner; basis regular, with posterior wing, width 0.71 as long, posterior distal corner rounded, hind margin crenulated, anterior margin with cuspidate setae; ischium subquadratic, with strong setae at thr anterior distal corner; merus broaden medially, with 6 strong cuspidate setae along posterior margin, with 4 strong cuspidate setae along anterior margin and with a cluster of 2–3 cuspidate setae at the posterior distal and anterior distal corners each; carpus 0.7 as long as merus, with single stout cuspidate seta at the anterior and posterior margins each, and with single clusters of cuspidate setae at the anterior and posterior distal corners each; propodus linear, more narrow and 1.1 times as long as carpus; dactylus small (1/3 of propodus), with nail.

Pereopod 6: ( Fig. 24 e, f) coxa with slightly rounded hind margin and with anterior lobe rounded down; basis regular, with posterior wing, width 0.7 as long, posterior distal corner rounded, hind margin crenulated, anterior margin with cuspidate setae; ischium subquadratic, with a group of cuspidate setae at the anterior distal corner; merus broaden medially, with 4 strong cuspidate setae along posterior margin, with 3 strong cuspidate setae along anterior margin and with a cluster of 2–3 cuspidate setae at the posterior distal and anterior distal corners each; carpus 0.82 as long as merus, with single clusters of cuspidate setae at the anterior and posterior distal corners each; propodus linear, more narrow and 1.3 times as long as carpus; dactylus small (1/3 of propodus), with nail.

Pereopod 7: ( Fig. 24 g, h) coxa small, without distinct anterior lobe and with rounded posterior lobe; basis regular, with rounded posterior wing, width 3/4 as length, hind margin crenulated, anterior margin with cuspidate setae; ischium subquadratic, with a group of cuspidate setae at the anterior distal corner; merus broaden medially, with 4 strong cuspidate setae along posterior margin, with 3 strong cuspidate setae along anterior margin and with a cluster of 2–3 cuspidate setae at the posterior distal and anterior distal corners each; carpus 0.84 times as long as merus, with 2 groups of 2 cuspidate setae at the anterior margin, and with a single clusters of cuspidate setae at the anterior and posterior distal corners each; propodus linear, 1.5 times as long as carpus, with 3 clusters of strong cuspidate setae along anterior and posterior margins each, with dense tuft of strong cuspidate setae near the base of dactylus; dactylus small (1/4 of propodus), with nail.

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

Epimeral plates 1–3 ( Fig. 25 a, b, c) produced ventroposteriorly, posterior margin slightly convex, distinctly serrated; plates 2 with two short stout setae along ventral margin; plates 3 with 5 short stout setae along ventral margin.

Pleopods: ( Fig. 25 d–h) normal, no sexual dimorphism; each peduncle with two coupling spines on the inner corner; coupling basis of inner ramus with 3 specific stout two-pointed plumose setae along inner margin.

Uropod 1: ( Fig. 25 i) peduncle with strong and curved interramal spur, with numerous tiny stout setae along inner and outer margins; rami subequal in length, 0.7 times as long as peduncle; rami with two groups of tiny stout setae along outer edge each, both rami with few tiny simple setae at the tip.

Uropod 2: ( Fig. 25 j) peduncle subequal to rami; inner ramus as long as outer ramus, both with 1–2 tiny stout setae along outer margin; uropod 2 1.6 times shorter than uropod 1.

Uropod 3: ( Fig. 25 k) peduncle 2 times shorter than outer ramus, with few small stout setae at the distal outer corner; inner ramus small, 0.17 times as long as outer ramus, scale-like, pointed apically, with one stout simple seta subapically; outer ramus elongate , uni-articulate, with 3 groups of small stout cuspidate setae along anterior and posterior margins each, with a group of small stout cuspidate setae at the apex.

Telson: ( Fig. 25 l) fully cleft; lobes diverging distally, pointed apically, medial and lateral notches are equidistant from the base; apical and subapical simple cuspidate setae long, lobes with single short cuspidate seta at the medial margin each.

Female (4.5 mm). Smaller than male. Vital body color is light-grey. Dorsal armament as in male ( Fig. 26 a).

Head: similar to that in male.

Antenna 1: ( Fig. 26 b) slender; flagellum 1.6 times as long as peduncle, 17–18 articles; peduncle article 1 subequal to article 2 in length, article 3 0.58 times as long as article 2; accessory flagellum small, 1+-articulate.

Antenna 2: ( Fig. 26 c) flagellum almost 0.39 times as long as peduncle, 6+ articles; peduncle articles 5 0.94 times as long as article 4, articles 1–3 together are 0.77 times as long as article 5 and 0.82 as long as article 4, articles 2 with protruding lobe almost reaching the distal end of next article.

Mouthparts: similar to those in male.

Labrum: ( Fig. 26 d) with rounded tip, frontal margin densely covered by minute setae.

Maxilla 1: ( Fig. 26 e) inner plate with truncate distal end, lined with a row of 8 plumose setae.

Pereopod 1: ( Fig. 27 a) coxa longer than in male; articles 2–5 as in male; rounded distally; palmar margin of propodus excavated at basal part of palmar margin, without a distinct protuberance at the middle; dactylus not bulged basally, without a tri-lobed process on inner margin.

Pereopod 2: ( Fig. 27 b, c) much smaller than in male, with sexual dimorphism; coxa longer than in male; basis with numerous long simple setae along posterior margin; ischium pubescent with specific fan-shaped small setae near the posterior distal corner; carpus more elongate than in male; propodus ovoid, palm oblique, serrate, palmar margin with two rows of short spine-like setae, and a stout corner setae; tip of dactylus with nail.

Pereopods 3 and 4 as in male.

Pereopods 5–7 ( Fig. 27 d–g): coxal 5 higher than the male; coxa 6 with distinct sexual dimorphism, anterior lobe elongate , hooked, apical part distorted; legs as in male; merus not extremely robust.

Coxal gills 2–6 large, oval. Coxal gill 6 distinctly smaller than gills 2–5.

Oostegits linear, with numerous long setae.

Epimeral plates 1–3 as in male.

Pleopods ( Fig. 27 h–j): similar to that in male; coupling basis of inner ramus of pleopods 1 and 2 with 4 specific stout two-pointed plumose setae along inner margin, of pleopods 1 with 3 specific stout two-pointed plumose setae.

Uropods 1–3 as in male.

Telson: ( Fig. 27 l) similar to that in male.

Sexual dimorphism: Coxal plates in female is longer than in male. Pereopod 2 in male bigger than in female; carpus of pereopod 2 in female more elongate than in male. Coxa 6 of female, anterior lobe forming a strong, “hooked” process.

Variations: In armament of uropod 3. In exemplars from estuaries of Aniva Bay basin the outer ramus with 3 groups of small stout cuspidate setae along anterior and posterior margins each. In the exemplar from lagoon lake Ptichje the outer ramus with 4 groups of small stout cuspidate setae along anterior and posterior margins each. Etymology. Named after the type locality in Sakhalin Island.

Ecology: Melita shimizui sakhalinensis was found in low part of estuaries and in marine lagoons at pebbles, sand and silt bottoms, from littoral to 6 m, saline waters, in salinities of 24 psu and more. Females with eggs in marsupium was found in August.

Distribution: Estuaries and lagoons of southern part of Sakhalin Island.

Remarks. Melita shimizui sakhalinensis ssp. nov. is morphologically identical to the nominant subspecies Melita shimizui ( Uéno, 1940) ( Uéno 1940; Yamato 1988). M. shimizui sakhalinensis differs from M. shimizui only by the structure of coxa 6 of females. Anterior lobe of coxa 6 (female of M. shimizui sakhalinensis ) more elongate than in nominant subspecies ( Figs. 27 e, m).

Figures

FIGURE 22. Melita shimizui sakhalinensis ssp. n., holotype, male: a—dorsal armament of urosome, b—cephalon, c—antenna 1, d—antenna 2, e—upper lip, f—left mandible, g—low lips, h—maxilla 1, i—maxilla 2; scale: b, c, d— 1 mm; e, f, g, h, i— 0.1 mm.

FIGURE 23. Melita shimizui sakhalinensis ssp. n., holotype, male: a—maxilliped, b, c—pereopod 1, d—pereopod 2 without coxall gill; scale: a, b, c— 0.1 mm; d— 1 mm.

FIGURE 24. Melita shimizui sakhalinensis ssp. 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: a, b, d, f, h— 1 mm; c, e, g— 0.1 mm.

FIGURE 25. Melita shimizui sakhalinensis ssp. n., holotype, male: a—epimer 1, b—epimer 2, c—epimer 3, d—pleopod 1, e—coupling 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—uropod 3, l—telson; scale: a – d— 1 mm; e – l— 0.1 mm.

FIGURE 26. Melita shimizui sakhalinensis ssp. n., paratype, female: a—lateral view, b—antenna 1, c—antenna 2, d—upper lip, e—maxilla 1; scale: a, b, c— 1 mm; d, e— 0.1 mm; а—female from Ptychje lake, b – e—female from estuary of Susuja river.

FIGURE 27. Melita shimizui sakhalinensis ssp. n., paratype, female: a – pereopod 1, b—pereopod 2, c—specifically setae from a cushion of posterior margin of ischium, d—coxa 5, e—coxa 6 without coxal gill, f—coxa 7, g—pereopod 5, h—pleopod 2, i—coupling setae of pleopod 2, j—coupling setae of pleopod 3, k—uropod 3, l—telson; scale: a, d, e, f, i, j, k, l— 1 mm; b, g, h— 0.1 mm; а – j—female from estuary of Susuja river, k, l—female from Ptychje lake; Melita shimizui (Uéno, 1940): m—coxa 6 of female (from Yamato 1988).

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.