Melita nitidaformis, Labay, 2003

Labay, Vjacheslav S., 2003, A new species of Melita Leach (Amphipoda: Melitidae) from oligosaline waters of Russian Far East, Zootaxa 356 (1), pp. 1-8 : 1-8

Melita nitidaformis sp. n.

Type material. All specimens were collected in Lake Tunaycha by V. S. Labay & D. S. Zavarzin. Holotype: male, 6,9 mm long, 22.08.200 1 in the Collection of Zoological Museum of Far East State University, Vladivostok: N X 19102 /Cr­933. Paratypes: 3 specimens, 16.08.200 1 in the Collection of Zoological Museum of Far East State University, Vladivostok : N X 19101 /Cr­932. 24 specimens, 16.08.200 1 in the Collection of Zoological Museum of Far East State University, Vladivostok: N X 19100 /Cr­931.

Diagnosis. Body without teeth, urosome 2 with 2 short spines on each side of middorsal line. Hind corner of epimeral plates slightly obtuse. Article 3 of maxilliped bilobed. Propodus of pereopod 2 (gnathopod 2) in male fully elongate with very oblique palm.

Description.

Largest male 8 mm, largest female 6,8 mm. Colour when alive grey.

Body slender, laterally compressed; abdominal segments without dorsal teeth or carinations ( Fig. 1a ). Urosome 2 with 2 short spines on each side of middorsal line ( Fig. 1b ). Head without rostrum and without inferior antennal sinus. Eyes small, round, black.

Antennula about 4/5 as long as body ( Fig. 2a ). Peduncle articles elongate; article 3 about 4/7 as long as article 1 and about 3/7 as long as article 2. Peduncle article 1 with a few short setae near ventral distal corner; article 2 with 10 transverse rows of short setae (3–5 setae per row) along dorsal and ventral margins and with a spine near ventral distal corner; article 3 with 6 transverse rows of short setae along dorsal margin and with 10­11 transverse rows of short setae along ventral margin. Flagellum 25­articulate; articles with a tuft of setae on dorsal and ventral distal angles; proximal and middle articles bearing additional 1–2 setae tufts along ventral margin. Accessory flagellum typical, 2­articulate; article 1 long, about 2/3 as long as article 1 of flagellum ( Fig. 2b ).

Antenna short, about ½ as long as antennula ( Fig. 2c ). Peduncle 5­articulate; articles 4 and 5 elongate, article 5 slightly shorter than article 4; both articles bearing 6–7 groups of short setae along ventral margin and distal setae tufts. Flagellum 7­articulate; each article with a middle tuft of setae and with distal setae.

Upper lip large, trapezoid to rounded, apex armed with numerous short setae ( Fig. 2d ).

Mandibles subquadrate, identical; pars molaris well developed, triturative; corpus mandibulae with a row of 6 curved scull­shaped plumose setae; lacinia mobilis with 5 teeth; palp 3­articulate, articles as long as 10: 26: 23, article 2 with few medial setae on posterior margin, article 3, medial and distal parts of posterior margin with long plumose setae ( Fig. 2f ).

Lower lip with distinct inner and outer lobes, setulose ( Fig. 2e ).

Maxilla 1 ( Fig. 2g ): outer lobe about 1,5 as long as inner lobe, with 4 terminal pairs of spines, anterior comb­like spine and posterior turn­pike­like spine, inner lobe with a distal row of 7 plumose setae; pulp 2­articulate, article 2 about twice as long as article 1, with a distal row of spines and a distal row of setae.

Maxilla 2 ( Fig. 2h ): inner lobe slightly shorter than outer one, with a row of 7 strong setae; both lobes with distal twin rows of setae.

Maxilliped ( Fig. 2i ): inner lobe with a spine on inner corner, bearing long setae along inner margin and a distal row of short setae; outer lobe with a row of club­shaped spines and 3 longitudinal rows of short setae along distal part of inner margin; palp 4­articulate, articles long as 10: 26: 18: 19, article 2 with a row of setae, article 3 bilobed, posterior lobe about 2/3 as long as anterior lobe, inner margin of both lobes with setae, outer lobe with setae in a group near outer corner, distally covered by short setae, article 4 claw­like, bifid, connected to inner lobe of article 3.

Coxal gills 2–6, simple, without additional lobes.

Pereopods 1–2 (gnatopods 1–2) of melitid form, pereopod 1 <pereopod 2.

Pereopod 1 (gnatopod 1) ( Fig. 3a ). Coxal plate with numerous short setae along rounded ventral margin. Basis elongate, anterior margin with long setae, posterior distal corner covered by numerous small spines. Ishium about 0,3 as long as basis, posterior distal corner trimmed with fur by short setae. Merus 1,5 as long as ishium, with few long setae along ventral margin of posterior quadrate lobe, distal part of posterior margin setulose. Carpus as long as total length of ishium and merus, about twice as long as propodus, with 6 groups of setae along posterior margin, anterior distal corner covered by short setae and bearing a transverse row of long setae. Propodus subrectangle, palm transverse, lined with 7 spines on posterior part, posterior margin with 3 bundles of setae, inner side with 2 transverse rows of short setae near posterior margin and 6 transverse groups of long setae along anterior margin including distal group. Dactylus very small, shorter than palm, curved.

Pereopod 2 (gnathopod 2) ( Fig 3b, c ). Coxal plate elongate, with rounded corners, bearing 13–14 short setae along ventral margin. Basis elongate, posterior margin with 2–3 long setae. Merus with a distinct lobe, posterodistal angle produced into a prominent acute tooth. Carpus short, triangular, posterior margin rounded, with 9 transverse tufts of setae. Propodus strong, fully elongate, much longer than merus and carpus together, palm very oblique, lined with double rows of numerous short spines and few boundles of long setae, undefined by a distinct angle, posterior margin with 9 transverse groups of setae, with length of setae increasing distally, inner side bearing 6­7 transverse tufts of setae along anterior and posterior margin. Dactylus strong, slightly longer than palm.

Pereopods 3–4 ( Fig. 4a, b ). Coxal plate 3 with parallel anterior and posterior margin, bearing numerous short setae along rounded ventral margin. Coxal plate 4 with distinct posteroventral lobe, ventral margin broad, rounded; ventral part of anterior margin, ventral margin and ventral part of posterior margin with numerous short setae. Basis elongate, narrow, with long setae along proximal half of hind margin and with 2 spines in distal half. Merus with convex anterior margin bearing 3 spines and distal group of spines, posterior margin with 3–4 tufts of short setae. Carpus about 0,4 times as long as merus, with 3–4 groups of setae along anterior and posterior margin and with a long spine on posterodistal angle. Propodus linear, slightly longer than carpus, armed with 4 tufts of short setae along posterior margin. Dactylus short, about ¼ as long as propodus.

Pereopod 5 ( Fig. 4c, d ): basis rectangle, with a distinct hind lobe, ventral margin of which rounded, anterior margin lined with numerous small spines, posterior margin crenulated with short setae. Merus broad­oviform, produced distally inot anterior and posterior rounded lobes, anterior margin lined with 7 groups of spines, posterior margin bearing 5 single spines and 1 distal group of spines. Carpus sublinear, about 0,7 as long as merus, with 3 groups of spines along anterior margin and with 2 groups of spines along posterior margin. Propodus linear, 1,2 times as long as carpus, armed with 3 groups of spines, posterodistal angle produced a specific tooth with 2 spines near base. Dactylus short, about 0,3 as long as propodus.

Pereopod 6 similar to pereopod 5, but more strongly and longer; propodus linear, 1,6 times as long as carpus, lined with 4 groups of spines ( Fig. 4e ).

Pereopod 7 similar to pereopod 6; propodus 1,4 times as long as carpus, with 4 pairs of spines (without distal) along anterior margin and with 2 pairs along posterior margin ( Fig. 4f ).

Epimeral plates 1–3 ( Fig. 3 : d–f): hind corner slightly obtuse; posterior margin of epimeral plate 3 wavy with short thin spines.

Pleopods normal; peduncle with few long plumose setae on outer margin and with one thin long coupling spine and one massive comb­like coupling spine on inner corner ( Fig. 4g ).

Uropods 1–3 ( Fig. 4h, i, j ). Apexes of uropod 1 and 2 ramous reaching end of uropod 3 peduncle. Uropod 1: peduncle 1,6 times as long as subequal ramous, with 3 spines along hind margin, each ramous bearing 2 groups of spines on posterior margin and 4 various spines terminally. Uropod 2 about 0,6 as long as uropod 1; length of peduncle and outer ramie subequal; outer ramie with 3 spines along hind margin; inner ramie slightly shorter than outer ramie, with 2 spines along hind margin; both ramous with 4 spines terminally. Uropod 3: peduncle more 3 times shorter than outer ramie, with 3 spines on anterior­distal corner; article 1 of outer ramie elongate with rare simple setae and 6 groups of spines along each margin, central group including 1 simple spine and 1 oat­like spine; article 2 of outer ramie small, short, concealed in terminal group of spines; inner ramie small, about 11 times shorter than outer ramie, with 1 spine preterminally.

Telson cleft nearly base, each lobe rather narrow, apex tooth­shaped with 2 short setae and 5 various spines, inner margin with 1 spine ( Fig 4k, l ).

Female differing from male in pereopods 1, 2 (gnathopods 1, 2). Pereopod 1 in female: ishium and merus covered by numerous small spines in distal part of posterior margin, but not short setae as in male; carpus in female more shorter than that in male, about 1,5 times as long as propodus ( Fig. 5a, b ). Pereopod 2 in female: ishium with numerous small spines in distal part of hind margin, but not bare as in male; propodus shorter than that in male, 1,5 times as long as carpus, palm oblique and subequal hind margin, with 7 pairs of spines ( Fig. 5c ).

Remarks. Melita nitidaformis sp. n. belongs to the species group of Melita with weakly armed dorsal abdominal segments. Melita koreana Stephensen, 1944 (= Melita rylovae Bulycheva, 1955 ) and Melita laevidorsum Stephensen, 1944 ( Stephensen, 1944: p. 39­46, figs. 6­9) are members of this group in Asia Far East.

Melita nitidaformis differs from M. koreana by the absence of teeth on the dorsal surface of urosome 2 and by a fully elongate propodus of pereopod 2 with very oblique palm, without felt of setae.

Melita nitidaformis differs from M. laevidorsum by the absence of a felt on the propodus of pereopod 2, a distinct posterior lobe on the base of pereopods 5–7 and a hind corner of epimeral plates 1–3 slightly obtuse, but not acute.

Melita nitidaformis differs from both M. koreana and M. laevidorsum by ecology: M. nitidaformis prefer the oligohaline waters of Tunaycha Lake, but not marine.

Melita nitidaformis differs from the ecologically and morphologically similar Melita nitida Smith, 1874 ( Smith, 1874: p. 560 ­561) by a bilobed article 3 of maxilliped and a fully elongate propodus of pereopod 2 (gnathopod 2) with very oblique palm.

Etymology. The specific name, nitidaformis , refers the morphological and ecological similarity to Melita nitida Smith, 1874 ( Bousfield, 1973) .

Distribution. Type locality only: Tunaycha Lake of southern Sakhalin Island, Russian Far East.

Ecology. Gravel, pebble and sandy bottom areas, on plants, from littoral to 10 m, oligohaline waters, in salinities 1,2–4,9%o.

Figures

FIGURE 1. Melita nitidaformis sp. n., a, entire animal, male, 8 mm (scale A); b, dorsal side of urosome 2.

FIGURE 2. Melita nitidaformis sp. n., holotype, male, 6,9 mm, a, antennula (B); b, accessory flagellum of antennula; c, antenna (B); d, upper lip (C); e, lower lip (C); f, left mandible (D); g, maxilla 1 (D); h, maxilla 2 (D); i, maxilliped (D).

FIGURE 3. Melita nitidaformis sp. n., holotype, male, 6,9 mm, a, pereopod 1 (E); b, pereopod 2 (F); c, propodus of pereopod 2, inner side; d­f, epimeral plates 1­3 (F).

FIGURE 4. Melita nitidaformis sp. n., holotype, male, 6,9 mm, a, pereopod 3 (G); b, pereopod 4 (G); c, pereopod 5 (G); d, apex of pereopod 5 propodus; e, pereopod 6 (G); f, pereopod 7 (G); g, pleopod 1 (G); h, uropod 1 (H); i, uropod 2 (H); j, uropod 3 (H); k, telson (H); l, apex of telson lobe.

FIGURE 5. Melita nitidaformis sp. n., female, 6 mm, a, pereopod 1 (I); b, propodus of pereopod 2; c, pereopod 2 (I).