Gammarus frigidus, Hou & Li, 2004

Hou, Zhong-E & Li, Shuqiang, 2004, Gammarus Species From Tibet Plateau, China (Crustacea: Amphipoda: Gammaridae), Raffles Bulletin of Zoology 52 (1), pp. 147-170 : 148-154

Gammarus frigidus , new species

( Figs. 1-5 )

Material examined. – Holotype - male, 13.1 mm (IZCAS-I-A0069), altitude 4500 m, living in a swamp of Nagqu County (31.4 oN, 92.0 oE), Tibet, China, 9 Sep.2001.

Paratypes - 15 males, 7 females, 2 juveniles ( IZCAS) , 8 males, 3 females ( ZRC), same data as holotype .

Diagnosis. – Gnathopod 1: propodus ovate, palm not deeply oblique, similar to that of female in shape. Uropod 3: inner ramus about 90% of article 1 of outer ramus, article 2 distinct, both rami fringed with plumose setae. Telson: with distal spines, but no dorsal spines. Maxilla 1: inner plate with about 19 plumose setae. Maxilla 2: inner plate densely setose, with a row of 32 plumose setae on inner face.

Description. – Holotype, 13.1 mm. Head ( Fig. 3A ): cephalic lateral lobe truncate, inferior antennal sinus deep, eyes ovate and medium in size. Antenna 1 ( Fig. 4A ): peduncular articles 1-3 in length ratio 1: 0.55: 0.3, with some distal setae; primary flagellum with 21 articles, most with aesthetascs; accessory flagellum with 3 articles. Antenna 2 ( Fig. 4B ): gland cone attaining peduncular article 3, article 4 about as long as article 5, both with 3 groups of setae on posterior margins; flagellum with 12 articles, some articles with calceoli.

Upper lip ( Fig. 1G ): subrounded, bearing minute setae. Mandibles ( Figs. 1A, C ), left incisor 5-dentate, lacinia mobilis with 4 teeth, molar triturative, article 2 of palp with 15 stiff setae, article 3 about 75% of article 2 in length, with 3 Asetae on outer face, 3 B-setae on inner face, about 15 D-setae and 5 E-setae; right incisor 4-dentate, lacinia mobilis bifurcate. Lower lip ( Fig. 1B ): inner lobe lacking. Maxilla 1 ( Figs. 1E, F ): inner plate with 19 plumose setae, article 2 of left palp with 7 slender spines and 2 stiff setae; article 2 of right palp with 5 blunt spines and 1 stiff seta. Maxilla 2 ( Fig. 1D ): inner plate densely setose, with 32 plumose setae, which are subparallel to inner margin; outer plate broad, bearing apical setae. Maxilliped ( Fig. 1H ): inner plate with 3 apical spines, outer plate with 11 spines on medial margin and 5 apical pectinate setae, palp with 4 articles.

Coxal plates: coxal plates 1-3 subrectangular ( Figs. 2A, C , 3C ), with 1-3 setae on anterior corner and 1 seta on posterior corner; coxal plate 4 excavated ( Fig. 3D ), as wide as long, with 2 and 5 setae on anterior corner and posterior margin, respectively; anterior lobe of coxal plates 5 and 6 small ( Figs. 5A, B ), posterior margin with 1-2 short setae; coxal plate 7 ( Fig. 5C ) with 6 setae on posterior corner.

Gnathopod 1 ( Figs. 2C, D ): basis short, with long setae on anterior and posterior margins; carpus about 75% of length of propodus; propodus pyriform, palm not very oblique, bearing 1 medial spine, and 9 spines on posterior margin; dactylus about half of posterior margin of propodus, with 1 seta on outer margin. Gnathopod 2 ( Figs. 2A, B ): carpus and propodus longer than those of gnathopod 1, carpus a little shorter than propodus, with subparallel margins; propodus subrectangular, palm transverse, bearing 1 medial spine and 4 spines on posterior corner; dactylus fitting the palm, with 1 seta on outer margin.

Pereopods 3 and 4 ( Figs. 3C, D, H, I ): pereopods 3 and 4 with long straight setae on posterior margins, articles 5 and 6 accompanied by several spines on posterior margin, dactylus slender, with 1 seta on anterior margin and 1-2 setae at joint of nail.

Pereopods 5-7 ( Figs. 5 A-F): subequal in length, anterior margin of bases weakly convex, with 5 short spines and several long setae proximally, posterior margin nearly straight in pereopod 5, weakly concave distally in pereopod 6, processed in pereopod 7, with a row of 13 short setae, inner face of pereopod 7 with a small seta; articles 4 and 5 mainly with 2-3 groups of spines along anterior and posterior margins; article 6 with 4-5 clusters of spines on anterior margin and some short setae on posterior margins; dactylus slender, with 1 seta on posterior margin and 2 setae at joint of nail.

Coxal gills ( Figs. 2A , 3C, D , 5 A-C): coxal gills of pereopods 2-7 flat.

Epimeral plates ( Fig. 4E ): epimeral plates 1-3 progressively acuminate on posterior corner, with 2-4 short setae on posterior margins; epimeral plate 1 ventrally rounded, with 10 setae on anterior corner; epimeral plate 2 with 5 spines on ventral margin and 1 subventral spine; epimeral plate 3 with 5 ventral spines. Pleopods ( Figs. 3 E-G): subequal in length, peduncle with some dorsal setae, bearing 2 retinacula accompanied by 1-3 setae; rami with about 22 articles, fringed with plumose setae.

Urosomites ( Figs. 1I , 3B ): urosomites 1 and 2 slightly elevated. Urosomite 1 with 3-2-1-3 spines on dorsal margin from left to right, urosomite 2 with 3-2-3 spines on dorsal margin, urosomite 3 with 2 spines-2 setae-2 spines on dorsal margin. Uropod 1 ( Fig. 4G ): peduncle longer than rami, with 1-1-2 and 1-1 spines on outer and inner margins, respectively; outer ramus with 1 and 2 spines on outer and inner margins, respectively; inner ramus with 3 spines on outer margin. Uropod 2 ( Fig. 4C ): peduncle with 2 spines on each side; outer ramus shorter than inner ramus, with 1 spine on each side; inner ramus with 2 spines on outer margin. Uropod 3 ( Fig. 4D ): peduncle with distal spines; length of inner ramus about 90% of article 1 of outer ramus, with 2 lateral spines; article 1 of outer ramus with 1-2-2 spines on outer margin and 3 distal spines, article 2 about 17% of length of article 1, both rami armed with plumose setae.

Telson cleft ( Fig. 4F ), each lobe with 3-4 distal spines accompanied by 3 setae and 2-3 dorsal short setae.

Female. – Body length 10.05 mm. Gnathopod 1 ( Fig. 5G ): similar to that of male in shape, with 2 spines on posterior margin and 5 spines on posterior corner. Gnathopod 2 ( Fig. 5H ): carpus and propodus elongate, propodus subrectangular, length about two times width, palm truncate, with 6 slender spines on posterior corner. Oostegites: present on pereopods 2-5.

Etymology. – The specific name comes from its biotope, the high altitude and frigid climate.

Remarks. – Gammarus frigidus belongs to the G. pulex -group (Karaman & Pinkster, 1977). Gammarus frigidus is closely related to G. lasaensis Barnard & Dai, 1988 in that maxilla 2 of both species have more than 30 plumose setae on the inner plate and their telsons are with few setae. Gammarus frigidus is separated from G. lasaensis by having an ovate propodus in the gnathopod 1 and an elongate inner ramus of the uropod 3, with nearly reaching the end of article 1 of outer ramus.

Gammarus frigidus is also similar to G. stagnarius Hou, Li & Morino, 2002 , in pereopods 3 and 4 with long straight setae on posterior margins, and the shape of epimeral plates 1-3. Gammarus frigidus is distinguished from G. stagnarius by antenna 2 with calcoli, propodus of gnathopod 1 ovate, and inner ramus of uropod 3 reaching about 90% of article 1 of outer ramus.

Distribution. – Nagqu, Tibet, China (present study).

Figures

Fig. 1. Gammarus frigidus, new species, male, holotype. A. left mandible, B. lower lip, C. incisor of right mandible, D. maxilla 2, E. palp of right maxilla 1, F. left maxilla 1, G. upper lip, H. maxilliped, I. urosomites 1-3 (dorsal view).

Fig. 2. Gammarus frigidus, new species, male, holotype. A. gnathopod 2, B. propodus of gnathopod 2, C. gnathopod 1, D. propodus of gnathopod 1.

Fig. 3. Gammarus frigidus, new species, male, holotype. A. head, B. urosomites 1-3 (lateral view), C. pereopod 3, D. pereopod 4, E. pleopod 1, F. pleopod 2, G. pleopod 3, H. dactylus of pereopod 3, I. dactylus of pereopod 4.

Fig. 4. Gammarus frigidus, new species, male, holotype. A. antenna 1, B. antenna 2, C. uropod 2, D. uropod 3, E. epimeral plates 1-3, F. telson, G. uropod 1.

Fig. 5. Gammarus frigidus, new species, male: A - F; female: G, H. A. pereopod 5, B. pereopod 6, C. pereopod 7, D. dactylus of pereopod 5, E. dactylus of pereopod 6, F. dactylus of pereopod 7, G. propodus of gnathopod 1, H. propodus of gnathopod 2.