Figs 4A, 42–47

Material examined. Holotype: male (IZCAS-I-A1081-1), 10.5 mm, from the protected areas of black-necked cranes (103.34°E, 26.68°N), altitude 2,502 m, Daqiao Village, Huize County, Qujing City, Yunnan Province, China, February 21, 2010, collected by L. Lin. Paratype: 1 female (IZCAS-I-A1081-2), 11.3 mm, same data as holotype.

Etymology. The specific name is from Latin margcomosus (spiny), in reference to coxal plates and epimeral plates with more small setae; adjective.

Diagnosis. Propodus of gnathopod I larger than that of gnathopod II; coxal plates of gnathopods I and II and pereopods III–VII apparently with more setae on anterior and posterior margins; inner ramus reaching about 0.7 times the length of outer ramus, both margins with plumose and simple setae; armature on urosome segments I and II non-existing or weak, urosome segment I dorsally bare, urosome segment II bare or with fewer tiny setae; epimeral plates I–III with a row of more than 10 setae on posterior margins.

Description of male. Holotype (IZCAS-I-A1081-1), male 10.5 mm (Fig. 4A).

Head (Fig. 42A): eyes reniform, 1.7 times as long as wide, inferior antennal sinus deep, lateral cephalic lobe nearly straight.

Antenna I (Fig. 42B, C): 1 st to 3 rd article of peduncle in length ratio 1.0: 0.9: 0.5, with setae on distal corner; flagellum with 25 articles, 2 nd to 23 rd article with aesthetascs; accessory flagellum with 4 articles; both primary and accessory flagella with short distal setae.

Antenna II (Fig. 42D): about 0.9 times as long as antenna I, 3 rd to 5 th article of peduncle in length ratio 1.0: 3.2: 3.4, 4 th and 5 th article of peduncle with 6–8 clusters of lateral and medial setae; flagellum with 10 articles and 1 tiny distal article, with setae along dorsal and ventral margins; calceoli absent.

Upper lip (Fig. 42E): ventral margin rounded, bearing minute setae.

Mandible (Fig. 42G, H): left mandible incisor with 5 teeth; lacinia mobilis with 4 teeth, spine row with 5 pairs of plumose setae along ventral margin; 1 st to 3 rd article of palp in length ratio 1.0: 3.6: 2.5, 2 nd article of palp armed with 18 marginal setae, 3 rd article with a row of 5 A-setae, 2 clusters of B-setae, 23 D-setae and 5 E-setae apically; incisor of right mandible with 4 teeth, lacinia mobilis bifurcate, with small teeth.

Lower lip (Fig. 42F): inner lobes lacking, outer lobes covered with thin setae.

Maxilla I (Fig. 42I–K): asymmetrical, left inner plate with 16 plumose setae on medial margin; outer plate with 11 robust serrated apical spines, each spine with small teeth; 2 nd article of palp with 10 slender spines and 3 stiff setae apically; 2 nd article of right palp with 6 stout spines and 1 slender spine, another type with 5 stout spines, 1 stiff seta and 1 slender spine.

Maxilla II (Fig. 42L): inner plate with 15 plumose facial setae in an oblique row; inner and outer plates with long setae apically.

Maxilliped (Fig. 42M): inner plate with 1 subapical and 3 stout apical spines, some plumose setae along lateral margin; outer plate bearing a row of blade spines and 3 plumose setae apically; 4 th article of palp hooked, with a group of setae at hinge of unguis.

Gnathopod I (Fig. 43A, C): coxal plate bearing 8 setae on anterior margin; basis with setae on anterior and posterior margins; carpus 1.3 times as long as wide, about 0.6 times as long as propodus, posterior margin bearing short setae; propodus oval, palm with 1 medial spine and 15 spines on posterior margin and surface; dactylus with 1 seta on outer margin.

Gnathopod II (Fig. 43B, D): coxal plate bearing 7 setae and 2 setae on anterior and posterior margins; basis with setae on anterior and posterior margins, posterodistal corner with short setae; carpus 2.0 times as long as wide, about 0.7 times as long as propodus, with parallel margins, bearing 6 clusters of setae along ventral margin, 2 clusters of setae on dorsal margin; propodus subrectangular, palm margin with 1 medial spine and 6 spines on lateral posterodistal corner; dactylus with 1 seta on outer margin.

Pereopod III (Fig. 44A, F): coxal plate bearing 6 setae and 1 seta on anteroventral and posterior margins; basis elongate, with setae along anterior and posterior margins; merus with 6 clusters of setae on posterior margin and 1 spine on anterior margin, anterodistal corner with 1 spine accompanied by setae; carpus and propodus with groups of spines accompanied by setae on posterior margin; dactylus with 1 plumose seta on posterior margin, and 2 setae at hinge of unguis.

Pereopod IV (Fig. 44B, G): coxal plate excavated, bearing 5 setae on anterior margin and 10 setae on posterior margin; basis with setae along anterior and posterior margins; merus with 4 clusters of setae on posterior margin and 1 spine on anterior margin, anterodistal with 1 spine accompanied by some setae; carpus and propodus with groups of spines accompanied by setae on posterior margin; dactylus with 1 plumose seta on anterior margin, and 2 setae at hinge of unguis.

Pereopod V (Fig. 44C, H): coxal plate bearing 3 setae on anterior margin and 11 setae on posterior margin; basis with 7 spines on anterior margin, anterodistal corner with 2 spines accompanied by some setae, posterior margin with a row of 19 setae; merus with 4 clusters of setae on anterior margin, anterodistal and posterodistal corners with 1 spine accompanied by setae respectively; carpus and propodus with groups of spines accompanied by setae on anterior margin, propodus with 2 clusters of setae on posterior margin; dactylus with 1 plumose seta on posterior margin, and 2 setae at hinge of unguis.

Pereopod VI (Fig. 44D, I): coxal plate bearing 7 setae on posterior margin; basis elongate, with 4 spines on anterior margin, anterodistal corner with 1 spine, posterior margin dwindling distally, with a row of 19 setae; merus with 2 clusters of single spine accompanied by setae along anterior margin and 1 spine on posterior margin, anterodistal and posterodistal corners with 2 and 1 spine accompanied by setae, respectively; carpus and propodus with groups of spines on anterior margin, propodus with 2 clusters of setae on posterior margin; dactylus with 1 plumose seta on posterior margin, and 2 setae at hinge of unguis.

Pereopod VII (Fig. 44E, J): coxal plate bearing 6 setae on posterior margin; basis expanded, posterior margin weakly narrowed distally, anterior with 2 clusters of setae and 5 spines, posterior with a row of 23 setae; merus to propodus with groups of spines accompanied by setae on anterior margins, propodus with 2 clusters of setae on posterior margin; dactylus with 1 plumose seta on posterior margin, and 2 setae at hinge of unguis.

Coxal gills: coxal gill of gnathopod II and gills of pereopods III–V nearly same as the length of bases; gill of pereopod VI more than half length of basis; gill of pereopod VII smallest, less than half of basis.

Epimeral plates (Fig. 43E–G): plate I ventrally rounded, bearing 10 long setae and 3 short setae on anteroventral margin and 8 setae on posterior margin; plate II with 2 spines on ventral margin and 14 setae on posterior margin, posterodistal corner blunt; plate III with 3 spines on ventral margin, and 14 setae on posterior margin, posterodistal corner blunt.

Pleopods I–III (Fig. 45B–D): similar, peduncle with 2 retinacula accompanied by 1–2 setae; outer ramus slightly longer than inner ramus, both rami fringed with plumose setae.

Urosome (Fig. 45A): dorsally flat, armature on doral margin non-existing or weak. Urosome segment I dorsally bare, urosome segment II bare or with few tiny setae on dorsal margin. Urosome segment III with 1 spine accompanied by 1 seta and 5 clusters of setae on dorsal margin.

Uropods I–III (Fig. 45E–G): uropod I peduncle without basofacial spine, with 2 spines on outer margin, 2 and 1 spine on outer and inner corners; outer ramus with 2 spines on outer margin and 1 spine on inner margin; inner ramus with 2 spines on inner margin; both rami with 5 terminal spines. Uropod II short, peduncle bearing 1 spine on outer and inner margins, with 2 and 1 distal spine on outer and inner corners; inner ramus with 1 and 2 spines on outer and inner margins, outer ramus shorter than inner ramus, with 1 spine on inner margin; both rami with 5 terminal spines. Uropod III peduncle with 3 distal spines accompanied by some setae; inner ramus about 1.5 times as long as peduncle, 0.7 times as long as outer ramus, with plumose setae on outer and inner margins, bearing 3 apical spines accompanied by simple setae; 1 st article of outer ramus with 3 spines accompanied by simple setae on outer margin, inner margin with 5 single plumose setae and 5 clusters of 1 simple seta accompanied by 1 plumose seta; terminal article obviously longer than adjacent spines.

Telson (Fig. 45H): deeply cleft, 0.8 times as long as wide, each lobe with 2 simple setae accompanied by 1 plumose seta on dorsolateral margin, with 1 apical spine accompanied by 5 setae.

Description of female. Paratype (IZCAS-I-A1081-2), 11.3 mm. Coxal plates and bases of gnathopods I and II and pereopods III–VII with more setae on posterior margins than those of male.

Gnathopod I (Fig. 46A, C): coxal plate bearing 13 fine setae and 2 setae on anterior and posterior margins, respectively; basis with setae on posterior margins; propodus oval, palm with 10 spines on posterior margin.

Gnathopod II (Fig. 46B, D): coxal plate bearing 8 fine setae and 2 setae on anterior and posterior margins; basis with setae on anterior and posterior margins, posterodistal corner with short setae; propodus subrectangular, palm margin with 4 spines on posterodistal corner, bearing simple setae along anterior and posterior margins; dactylus with 1 seta on outer margin.

Pereopods III and IV (Fig. 47A–B): with fewer straight setae on posterior margin than those of male.

Pereopods V–VII (Fig. 47C–E): bases with fewer setae on posterior margin than those of male.

Epimeral plates (Fig. 47F–H): similar to those of male, with more setae on posterior margins.

Uropods I–III (Fig. 45I–K): uropod I peduncle without basofacial spine, with 2 spines on outer and inner margins, with 2 and 1 spine on outer and inner corners; both rami with 2 spines on inner margins and 5 terminal spines. Uropod II similar to that of male. Uropod III peduncle with 4 distal spines; inner ramus 1.2 times as long as peduncle, reaching 0.7 times the length of outer ramus, with 2 spines and some plumose setae on lateral margin; 1 st article of outer ramus with 2 single spines and 1 pair of spines accompanied by setae on outer margin, inner margin with 3 single plumose setae and 2 clusters of 1 simple seta accompanied by 1 plumose seta; terminal article slightly longer than adjacent spines.

Telson (Fig. 46I): cleft, similar to those of male.

Oostegite (Fig. 46E–H): oostegite of gnathopod II broad, with marginal setae, oostegites of pereopods III and IV elongate, oostegite of pereopod V smallest.

Variability. Urosome segment II bare or with fewer tiny setae; 2 nd article of right palp with 6 stout spines and 1 slender spine, or with 5 stout spines, 1 stiff seta and 1 slender spine.

Habitat. This species was collected along the bank of a lake in protected areas of black-necked cranes.

Remarks. Gammarus margcomosus sp. nov. is similar to G. platvoeti Hou & Li, 2003 in: calceoli absent; armature on urosome segments I and II non-existing or weak; both margins of inner ramus and inner margin of uropod III outer ramus with plumose setae. The new species can be distinguished from G. platvoeti by the following characters (G. platvoeti in parentheses): coxal plates of gnathopods I and II and pereopods III–VII with more setae on anterior and posterior margins (with fewer setae); bases of pereopods III–VII with more setae on posterior margins (with fewer setae); inner ramus reaching about 0.7 times the length of outer ramus, terminal article longer than adjacent spines (inner ramus about 0.8 times the length of outer ramus, terminal article shorter than adjacent spines); epimeral plates I–III with more setae on posterior margins, posterodistal corners of plates II and III subacute (with fewer setae on posterior margins, posterodistal corners of plates II and III acute); urosome segments I and II without or with few tiny setae on dorsal margin, urosome segment III with 1 spine accompanied by 1 seta and 5 clusters setae on dorsal margin (urosome segments I and II with 2 setae on medial-dorsal margins; urosome segment III with 2 clusters of single spine and some setae on medial-dorsal margin).