Gammarus montaniformis, Sidorov, Dmitry A., 2012

Sidorov, Dmitry A., 2012, Two new species of freshwater amphipods (Crustacea: Gammaridae) from Central Asia, with comments on the unusual upper lip morphology, Zootaxa 3317, pp. 1-24 : 2-12

Gammarus montaniformis sp. nov.

Figures 1–44

Diagnosis. G. montaniformis sp. nov. belongs to the pulex species group with numerous long setae on pereopods 3 and 4 and uropod 3. Body stout, robust ( Fig. 1 ), dorsal surface of body segments smooth. Inferior antennal sinus shallow, sub-rounded ( Fig. 4 ). Antenna 1 25–35 % longer than antenna 2. Antenna 2 bearing calceoli in male. Coxal plate of gnathopod 1 ( Figs 17 , 34 ) has a broadly dilated ventral margin. Dorsal surface of urosomites 1–3 ( Fig. 5 ) armed with robust notched setae on the following manner: 1 (0-0-0-0), 2 (1-1-1-1), 3 (2-0-0-2). Uropod 3 bearing simple and plumose setae on both rami. Body length 11.5 mm (female), 9.0– 9.5 mm (males).

Material examined. Holotype: male, 9.5 mm, X31193 /Cr-1367- FESU, Kazakhstan, Dzungarian Alatau, Kojandytau Mountains, Sarlytan Canyon, Borohudzyr River (44º 45.115 N; 79º 54.646 E), 14 Oct. 2010, 2193 m above sea level, coll. D.I. Berman, T.N. Dujsebaeva. Paratypes: 16/1sd-IBSS, 2 female (7.0 mm, 7.8 mm), 1 male, (9.0 mm, 11.5 mm), with same data as holotype.

Description. Male (9.5 mm, holotype). Head. Antenna 1 ( Fig. 2 ): 55–60% length of body, about 25% longer than antenna 2; peduncular articles 1–3 have a length ratio of 1:0.70:0.35; primary flagellum with 23 articles, almost all flagellar articles bearing lanceolate aesthetascs accompanied by setae; accessory flagellum 3–articulate, terminal article small, bearing 3 simple setae. Antenna 2 ( Fig. 3 ): gland cone acute without setae; peduncular article 4 as long as article 5, both articles setose with short stiff setae; flagellum non flattened with 11+1 articles, calceoli present. Mandibles subequal: left mandible ( Fig. 6 ) with incisor 5–dentate, lacinia mobilis 5–dentate, setal row with 5 serrate setae, triturative molar with plumose seta; palp article 2 ( Fig. 8 ) 0.25 × longer than article 3 with 3 long and 9 short setae, article 3 bearing 4 A-setae, 4 B-setae, 22 D-setae and 5 E-setae; incisor of right mandible ( Fig. 7 ) 5–dentate, lacinia mobilis bifurcate, setal row with 5 serrate setae. Maxilla 1, right ( Fig. 12 ): inner plate with 12 plumose setae, outer plate with 11 pectinate robust setae; right palp massive, palp articles 1–2 have a length ratio of 0.25:1, article 2 bearing 4 strong pointed peg setae, 1 serrate and 1 plumose setae on apex; left palp feeble ( Fig. 13 ), articles 1–2 have a length ratio of 0.25:1, article 2 bearing 5 short strong and 3 stiff setae on apex. Maxilla 2 ( Fig. 11 ): inner plate with oblique row of 8–10 plumose setae on inner margin; outer plate slightly broader than inner plate with 4 stiff serrate and 8–12 slender setae on apex. Upper lip ( Fig. 10 ): subrhomboid, with minute setae at apex. Lower lip ( Fig. 9 ): inner lobes absent. Maxilliped ( Fig. 14 ): peduncle trapeziform with sets of long setae on inner face; inner plate ( Fig. 16 ) with 3 simple strong peg setae on apex and with 1 same setae sub-apically, 5 long simple setae on apex and 14 plumose setae extending from inner margin to apex; outer plate ( Fig. 15 ) with a row of 10 medial robust serrate setae and with parallel row of 16 small stiff setae, 5 plumose setae on apex; palp four articulate, article 2 weak with 2 serrate setae at outer margin.

Pereon. Gnathopod 1 ( Fig. 17 ): coxal plate deep, ventral margin dilated with 2 short setae on anterior and posterior corners; basis stout with long plumose setae on anterior and posterior margins; carpus 0.65 × as long as propodus; propodus of gnathopod 1 ( Fig. 18 ) as long as propodus of gnathopod 2 or slightly longer; propodus subtriangular, ovate, palm concave with cutting margin developed and armed with 1 distally notched robust setae on medial face, 2 long distally notched robust setae near defining angle; posterior margin as long as palm bearing four groups of peg notched setae; dactylus with 1 seta on outer face, nail long. Gnathopod 2 ( Fig. 19 ) some larger than gnathopod 1; coxal plate deep ventral margin narrowed with 4 short setae on anterior and posterior corners; basis stout with long plumose paired setae on anterior and posterior margins; carpus 0.70 × as long as propodus; propodus sub-rectangular ( Fig. 20 ), palm deeply concave with cutting margin developed and armed with 1 distally notched robust setae on medial face, two pairs of distally notched robust setae near defining angle one of them long; posterior margin 2 × longer than palm with 8 sets of plumose setae; dactylus similar to that of gnathopod 1. Pereopod 3 ( Fig. 26 ): shorter than pereopods 5–7; coxal plate deep with 6 short setae on ventral margin; basis sublinear with sets of long setae on posterior margin; merus densely setose with 9 sets of long uncurved setae on posterior margin and armed with 3 strong notched setae at disto-anterior corner; carpus setose with 6 sets of long setae accompanied by 5 short robust setae on posterior margin; propodus setose with long setae accompanied by 5 short robust setae; dactylus about 50% length of corresponding propodus, bearing 1 plumose seta on outer margin and 2 setae in base of nail. Pereopod 4 ( Fig. 27 ): sub-similar to pereopod 3 but slightly shorter; coxal plate sub-quadrate bearing 5 short setae along ventral margin. Pereopods 5–7 ( Figs 28–30 ): stout, sub-similar but pereopod 5 shortest; pereopods 6 and 7 equal in length or 7 slightly shorter; coxal plates 5 and 6 bilobate, posterior lobes broader than anterior ones and armed with 3 short setae on posterior margin; bases with slightly serrate posterior margins, distoposterior lobes rounded, disto-posterior margins almost straight or scarcely sinuate; carpi 6 and 7 1.2 × as long as corresponding meri; posterior margins of propodi 5 and 6 bearing robust setae accompanied by simple thin setae; dactyli about 30–35% length of corresponding propodi, bearing 1 plumose seta on outer margin and 2 setae in base of nail. Coxal gills 2–7 ( Figs 19 , 26 , 30 ) stalked and saccular.

Pleon. Epimera 1–3 ( Fig. 21 ): epimeron 1 with 5 long and 1 robust notched setae on anteroventral corner, posterior margin with 2 setae; epimeron 2 posterior margin convex, bearing 3 robust notched setae on subventral margin and 3 setae on posterior margin; epimeron 3 disto-posterior corner weakly produced, bearing 3 robust notched setae on sub-ventral margin and 4 setae on posterior margin. Pleopods 1–3 ( Figs 31–33 ): subequal, peduncle with 2 or 3 retinacula each accompanied by 1 plumose seta on anterior corner; 2 or 3 bifurcate setae on outer margin of first article of inner ramus; rami sub-equal in length and fringed with plumose setae. Urosome ( Figs 1 , 5 ): urosomites 1–3 dorsally flat with 4 groups of robust notched and sparse fine setae. Uropod 1 ( Fig. 22 ): peduncle with 1 basofacial notched seta, outer margin with 5 and inner margin with 1 setae; inner ramus 0.8 × as long as outer ramus, 50% length of peduncle; inner ramus with 1 seta on inner margin; outer ramus with 1 and 2 setae on inner and outer margins correspondingly; both rami with 4 distal simple setae. Uropod 2 ( Fig. 23 ): peduncle 0.25 × longer than both rami, with 3 and 2 notched setae on inner and outer margins correspondingly; both rami equal in length, outer ramus with 1 notched seta on inner and outer margins; inner ramus with 1 notched setae on inner margin; both rami with 2 sub-distal and 3 distal notched setae. Uropod 3 ( Fig. 24 ): biramous; peduncle with 2 setae on lateral surface and two groups of robust setae at distal margin; inner ramus as long as peduncle and about 0.4 × as long as outer ramus, inner and outer margins with simple and plumose setae; proximal article of outer ramus with 3 robust setae and 9 sets of long simple setae on outer margin, inner margin densely setose with long simple and plumose setae, terminal article shorter than 4 adjacent notched setae. Telson ( Fig. 25 ): as long as uropod 3 peduncle; as long as broad, cleft about 90% of its length; each lobe with 2 sub-apical notched setae accompanied by long thin setae.

Female (7.8 mm). Similar to male but with smaller body size and differing in the following characteristics. Head. Antenna 1 ( Fig. 40 ): 70% length of body, about 35% longer than antenna 2; peduncular articles 1–3 have a length ratio of 1:0.60:0.35; primary flagellum with 18 articles, almost all flagellar articles bearing small lanceolate aesthetascs accompanied by setae; accessory flagellum 3–articulate, terminal article small, bearing 3 simple setae. Antenna 2 ( Fig. 41 ): gland cone acute without setae; peduncular article 4 slightly longer than article 5, both articles setose with long setae; flagellum with 7+1 articles, calceoli absent.

Pereon. Propodus of gnathopod 1 ( Fig. 34 ) longer than propodus of gnathopod 2, ovate, palm convex with cutting margin developed and armed with 3 distally notched robust setae near defining angle; posterior margin as long as palm bearing 4 distally notched robust setae; dactylus with 1 seta on outer face, nail long. Gnathopod 2 ( Fig. 35 ) some longer but feeble than gnathopod 1; carpus as long as propodus or slightly longer; propodus subrectangular, palm slightly convex with cutting margin developed and armed with two pairs of distally notched robust setae near defining angle; posterior margin about 1.5 × longer than palm with 4 sets of plumose setae; dactylus similar to that of gnathopod 1. Pereopods 5–7 ( Figs 42–44 ) similar to that of male but differs by more extended bases. Oostegites on gnathopod 2 ( Fig. 35 ) and pereopods 3–5 unmatured without marginal setae.

Pleon. Uropod 1 ( Fig. 36 ): peduncle without basofacial seta, outer margin with 4 and inner margin with 1 setae; inner ramus as long as outer ramus, 55% length of peduncle bearing 1 seta; outer ramus with 2 setae; both rami with 4 distal notched setae. Uropod 2 ( Fig. 37 ): peduncle 0.25 × longer than both rami, with 4 notched setae on margins; both rami sub-equal in length, outer ramus with 2 notched setae one of them long; inner ramus bearing 1 seta; both rami with 2 long sub-distal and 3 distal setae. Uropod 3 ( Fig. 38 ): inner ramus as long as peduncle and 0.5 × as long as outer ramus, bearing 2 long setae apically; proximal article of outer ramus with 4 robust setae on outer margin, both margins densely setose with long simple setae, terminal article longer than 5 adjacent notched setae. Telson ( Fig. 39 ): similar to that of male; as long as uropod 3 peduncle; slightly broader than long, cleft about 90% of its length; each lobe with 2 or 3 sub-apical notched setae accompanied by long thin setae.

Variability. The species is not extremely variable. The examined paratypes have variations in setation pattern of both plates of second maxilla and number of sub-apical notched setae of telson.

Taxonomic comments. G. montaniformis sp. nov. most resembles G. montanus Hou, Li & Platvoet, 2004 but can be distinguished from the latter by the presence of calceoli in male, more elongate propodi of the male gnathopod 2, mix of simple and plumose setae on both rami of uropod 3, by the different character of urosome armament and by the furnishing with long setae of uropod 3 as well as the different character of telson armament in female.

Gammarus montaniformis sp. nov. reveals minute similarities with some of the well known congeners from adjacent regions. Comparison with these species are presented below:

Because of the shape of gnathopod 1 and 2 propodi and coxal plate 1 (which has a broadly dilated ventral margin) the species could possibly be confused with G. laticoxalis Karaman & Pinkster, 1977 described from Syria and G. sirvannus Hekmatara, Sari & Heidary Baladehi, 2011 reported from Iran, but the armament of gnathopod 1 and 2 propodi, structure of uropod 3, epimera and telson are different. However, a number of described Gammarus species possess somewhat distally dilated coxal plate 1, e.g., G. montanus , G. brevipodus Hou, Li & Platvoet, 2004 , G. takesensis Hou, Li & Platvoet, 2004 has previously been reported from a close part of the Ili River in China, and G. topkarai Özbek & Balik, 2009 from South Anatolia, but G. montaniformis sp. nov. differs from above species in the shape and armament of uropod 3.

Type locality. Eastern Tien-Shan, Dzungarian Alatau, Kojandytau mountains, Borohudzyr River 44º 45.115 N; 79º 54.646 E.

Ecology. The amphipod G. montaniformis sp. nov. inhabits running freshwaters in the Ili River basin, Balkhash Lake basin. The coxal gills of some specimens were parasitized by the suctorial infusoria Dendrocometes ( Fig. 26 ).

Etymology. Species epithet montaniformis (lat.) adjective refers to the morphological and ecological similarity to G. montanus Hou, Li & Platvoet, 2004 .

Figures

FIGURE 1. Gammarus montaniformis, sp. nov., from left side, male, 9.0 mm, paratype.

FIGURES 2 – 10. Gammarus montaniformis, sp. nov., male, 9.5 mm, holotype: (2) antenna 1; (3) antenna 2, lateral view; (4) head; (5) urosome; (6) mandible, left; (7) mandible, right; (8) mandibular palp; (9) lower lip; (10) upper lip. Scale bars 0.2 mm, if not indicated otherwise.

FIGURES 11 – 16. Gammarus montaniformis, sp. nov., male, 9.5 mm, holotype: (11) maxilla 2; (12) maxilla 1, right; (13) palp of maxilla 1, left; (14) maxilliped; (15) outer plate of maxilliped; (16) inner plate of maxilliped. Scale bars 0.2 mm.

FIGURES 17 – 20. Gammarus montaniformis, sp. nov., male, 9.5 mm, holotype: (17) gnathopod 1; (18) propodus of gnathopod 1; (19) gnathopod 2; (20) propodus of gnathopod 2. Scale bars 0.2 mm.

FIGURES 21 – 27. Gammarus montaniformis, sp. nov., male, 9.5 mm, holotype: (21) epimera 1 – 3; (22) uropod 1; (23) uropod 2; (24) uropod 3; (25) telson; (26) pereopod 3; (27) pereopod 4. Scale bars 0.2 mm.

FIGURES 28 – 33. Gammarus montaniformis, sp. nov., male, 9.5 mm, holotype: (28) pereopod 5; (29) pereopod 6; (30) pereopod 7; (31) pleopod 1; (32) pleopod 2; (33) pleopod 3. Scale bars 0.2 mm.

FIGURES 34 – 35. Gammarus montaniformis, sp. nov., female, 7.8 mm, paratype: (34) gnathopod 1; (35) gnathopod 2. Scale bars 0.2 mm.

FIGURES 36 – 44. Gammarus montaniformis, sp. nov., female, 7.8 mm, paratype: (36) uropod 1; (37) uropod 2; (38) uropod 3; (39) telson; (40) antenna 1; (41) antenna 2; (42) pereopod 5, in part; (43) pereopod 6, in part; (44) pereopod 7, in part. Scale bars 0.2 mm.