Gammarus mosuo Hou & Li

Hou, Zhonge, Zhao, Shuangyan & Li, Shuqiang, 2018, Seven new freshwater species of Gammarus from southern China (Crustacea, Amphipoda, Gammaridae), ZooKeys 749, pp. 1-79 : 23-28

Gammarus mosuo Hou & Li sp. n. Figs 33, 34, 35, 36, 37, 38

Material examined.

Holotype: male (IZCAS-I-A1570-1), 8.0 mm, Yanyuan County (101.53°E, 27.40°N), altitude 2620 m, Xichang City, Sichuan Province, China, March 23, 2014, collected by Yunchun Li and Jincheng Liu. Paratype: female (IZCAS-I-A1570-2), 6.4 mm, same data as holotype.

Etymology.

The name derives from the Mosuo people, living in the type locality; noun in apposition.

Diagnosis.

Antenna II calceoli absent; merus to carpus of pereopod III with clusters of long setae on posterior margins; pereopods V–VII with long setae on anterior margins; epimeral plate II with five plumose setae, two simple setae and one spine on ventral margin, posterodistal corner blunt; urosomites with two clusters of spines accompanied by setae on dorsal margins; inner ramus of uropod III reaching 0.4 times the length of outer ramus, both inner and outer rami armed with simple setae.

Description of holotype male

(IZCAS-I-A1570-1). 8.0 mm.

Head (Fig. 33A): eyes oval, inferior antennal sinus deep.

Antenna I (Fig. 33B, C): peduncle articles I–III in length ratio 1.0: 0.6: 0.4, with distal setae; flagellum with 20 articles, articles III–IX with aesthetascs; accessory flagellum with three articles; both primary and accessory flagella with short distal setae.

Antenna II (Fig. 33D): peduncle articles III–V in length ratio 1.0: 2.9: 2.9, articles IV and V with lateral and medial setae; flagellum with seven articles, each article with numerous setae; calceoli absent.

Upper lip (Fig. 33E): ventral margin rounded, bearing short minute setae.

Mandible (Fig. 33G, H): left mandible incisor with five teeth; lacinia mobilis with four teeth; spine row with five pairs of plumose setae; articles I–III of palp in length ratio 1.0: 2.9: 2.2, second article with 13 marginal setae, article III with three A-setae, three B-setae, a row of D-setae, and six E-setae apically; incisor of right mandible with four teeth, lacinia mobilis bifurcate, with small teeth.

Lower lip (Fig. 33F): inner lobes lacking, outer lobes covered with thin setae.

Maxilla I (Fig. 33I, J): asymmetrical, left inner plate with 11 plumose setae on medial margin; outer plate with 11 robust serrated apical spines; second article of left palp with seven slender spines apically; second article of right palp with four stout spines, one stiff seta and one slender spine.

Maxilla II (Fig. 33K): inner plate with ten plumose facial setae in an oblique row; inner and outer plates with long setae apically.

Maxilliped (Fig. 33L): inner plate with four stout apical spines, one subapical spine, and 15 plumose setae; outer plate bearing a row of 14 blade spines and two plumose setae apically; article IV of palp hooked, with three setae at hinge of unguis.

Pereon.Gnathopod I (Fig. 34A, B): coxal plate bearing two setae and one seta on anterior and posterior margins, respectively; basis with long setae on anterior and posterior margins; merus bearing setae on posterodistal corner; carpus 1.8 times as long as wide, 0.8 times as long as propodus, bearing clusters of setae along ventral margin and two clusters of setae on dorsal margin; propodus oval, palm with one medial spine and 11 spines on posterior margin and surface; dactylus with one seta on outer margin.

Gnathopod II (Fig. 34C, D): coxal plate bearing three setae and one seta on anterior and posterior margins, respectively; basis with setae on anterior and posterior margins; merus bearing setae on posterodistal corner; carpus 1.7 times as long as wide, 0.9 times as long as propodus, bearing five clusters of setae along ventral margin and two clusters of setae on dorsal margin; propodus subrectangular, palm margin with one medial spine and four spines on posterodistal corner; dactylus with one seta on outer margin.

Pereopod III (Fig. 35A, B): coxal plate bearing two setae and one seta on anterior and posterior margins, respectively; basis elongated, with setae along anterior and posterior margins; merus with eight clusters of long setae on posterior margin and one spine accompanied by one seta on anterior margin, anterodistal corner with one spine accompanied by setae; carpus with two spines accompanied by groups of long setae on posterior margin, anterodistal corner with one spine accompanied by setae and posterodistal corner with two spines accompanied by setae; propodus with three pairs of spines accompanied by setae on posterior margin and two spines on posterodistal corner; dactylus with one plumose seta on anterior margin, and two setae at hinge of unguis.

Pereopod IV (Fig. 35C, D): coxal plate concave, bearing two setae on anterior margin and seven setae on posterior margin; basis with setae along anterior and posterior margins; merus with five clusters of setae on posterior margin and one spine accompanied by two setae on anterior margin, anterodistal corner with one spine accompanied by setae; carpus and propodus with spines accompanied by setae on posterior margins; dactylus with one plumose seta on anterior margin, and two setae at hinge of unguis.

Pereopod V (Fig. 35E, F): coxal plate bearing one seta and three setae on anterior and posterior margins, respectively; basis expanded, with two setae and four spines accompanied by setae on anterior margin, anterodistal corner with two spines accompanied by setae, posterior margin with a row of 17 setae; merus with four clusters of setae on anterior margin and one spine accompanied by two setae on posterior margin, anterodistal corner with one spine accompanied by setae and posterodistal corner with two spines accompanied by setae; carpus and propodus with groups of spines accompanied by fine setae on anterior margins; dactylus with one plumose seta on posterior margin, and two setae at hinge of unguis.

Pereopod VI (Fig. 35G, H): coxal plate bearing two setae on posterior margin; basis elongated, with two clusters of long setae and four spines accompanied by short setae on anterior margin, anterodistal corner with two spines accompanied by setae, posterior margin with a row of 14 setae; merus with four clusters of setae on anterior margin and one spine accompanied by two setae on posterior margin, anterodistal and posterodistal corners with two and three spines accompanied by setae respectively; carpus with three groups of spines accompanied by straight setae on anterior margin; propodus with three groups of spines accompanied by fine setae on anterior margin; dactylus with one plumose seta on posterior margin, and two setae at hinge of unguis.

Pereopod VII (Fig. 35I, J): coxal plate with five setae on posterior margin; basis with two clusters of long setae and four spines accompanied by setae on anterior margin, anterodistal corner with one spine accompanied by setae, posterior margin with a row of 13 setae; merus with four clusters of setae on anterior margin and one spine accompanied by two setae on posterior margin, anterodistal and posterodistal corners with three and two spines accompanied by setae, respectively; carpus with four groups of spines accompanied by straight setae on anterior margin; propodus with groups of spines accompanied by fine setae on anterior margin; dactylus with one plumose seta on posterior margin, and two setae at hinge of unguis.

Coxal gills: coxal gill of gnathopod II and gill of pereopod IV a little longer than bases; gills of pereopods III, V and VI shorter than bases; gill of pereopod VII smallest, less than half of the basis.

Pleon.Epimeral plates (Fig. 33 M–O): plate I ventrally rounded, bearing eight long setae on anteroventral margin and five setae on posterior margin; plate II with five sub-plumose setae, two simple setae and one spine on ventral margin and six setae on posterior margin, posterodistal corner blunt; plate III with four setae and one spine on ventral margin and six setae on posterior margin, posterodistal corner subacute.

Pleopods I–III (Fig. 36 A–C): similar, peduncle with two or three retinacula accompanied by one seta; outer ramus slightly shorter than inner ramus, both rami fringed with plumose setae.

Urosome.Urosomites (Fig. 34E): urosomite I with one spine accompanied by six setae on each side and one seta on dorsal margin; urosomite II with one and two spines accompanied by setae on each side; urosomite III with one spine accompanied by three setae on each side.

Uropods I–III (Fig. 36 D–F): uropod I peduncle with one basofacial spine, one and three spines on inner and outer margins, respectively, inner and outer distal corners with one spine each; inner ramus with one spine on inner margin; outer ramus with one spine and two spines on inner and outer margins, respectively; both rami with five terminal spines. Uropod II short, peduncle bearing one seta and one spine on inner and outer margins respectively, one distal spine accompanied by one seta on inner corner and one spine on outer corner; inner ramus with two spines on inner margin and one spine on outer margin; outer ramus with two spines on inner margin; both rami with five terminal spines. Uropod III peduncle with two setae on surface and six distal spines; both inner and outer rami armed with simple setae, inner ramus 0.9 times as long as peduncle, reaching 0.4 times the length of outer ramus, with one spine accompanied by two simple setae on inner margin and two spines accompanied by long setae distally; proximal article of outer ramus with three groups of spines accompanied by simple setae on outer margin, simple setae on inner margin, and four distal spines, terminal article with simple setae, slightly shorter than adjacent spines.

Telson (Fig. 36G): deeply cleft, 0.9 times as long as wide, each lobe with two plumose setae on surface and with one distal spine accompanied by three or four simple setae and a plumose seta.

Description of paratype female

(IZCAS-I-A1570-2). 6.4 mm.

Pereon.Gnathopod I (Fig. 37A, B): coxal plate bearing one seta on anterior and posterior margins each; basis with long setae on anterior and posterior margins; propodus oval, palm with five spines on posterior margin, bearing long setae along anterior and posterior margins; dactylus with one seta on outer margin.

Gnathopod II (Fig. 37C, D): coxal plate bearing two setae and one seta on anterior and posterior margins, respectively; basis with setae on anterior and posterior margins; propodus subrectangular, palm margin with three spines on posterodistal corner, bearing long setae along anterior and posterior margins; dactylus with one seta on outer margin.

Pereopod III (Fig. 38A): similar to that of male.

Pereopod IV (Fig. 38B): merus and carpus with longer setae on posterior margins than that of male.

Pereopod V (Fig. 38C): similar to that of male; basis to carpus with a few plumose setae on anterior or posterior margins.

Pereopods VI–VII (Fig. 38D, E): similar to those of male, but with more setae on anterior margins.

Oostegite (Fig. 37 E–H): oostegite of gnathopod II broad, with marginal setae, oostegites of pereopods III and IV elongated, oostegite of pereopod V smallest.

Urosome.Uropods I–III (Figs 36H, I; 38F): uropod I peduncle with one basofacial spine, one and two spines on inner and outer margins, respectively, inner distal corner with one spine and outer distal corner with two spines; inner ramus with one spine on inner margin; outer ramus with one spine on inner and outer margins each; both rami with five terminal spines. Uropod II short, peduncle bearing one spine on outer margin, each corner with one distal spine; both rami with one spine on inner margin and five terminal spines. Uropod III peduncle with three setae on surface and six distal spines accompanied by setae; both inner and outer rami with simple setae, inner ramus approx. as long as peduncle, reaching 0.6 times the length of outer ramus, with one spine accompanied by one seta on inner margin and one spine accompanied by long setae distally; proximal article of outer ramus with three spines accompanied by simple setae on outer margin and simple setae on inner margin, terminal article slightly shorter than adjacent spines.

Telson (Fig. 36J): cleft, 1.2 times as long as wide, each lobe with two simple setae on surface and with two distal spines accompanied by one simple seta and one plumose seta.

Habitat.

This species was collected under decomposing leaves alongside a pool.

Remarks.

The new species of Gammarus mosuo Hou & Li, sp. n. is most similar to G. sinuolatus Hou & Li, 2004b in propodus of gnathopod II with long straight setae on anterior margin; pereopods III and IV with long setae on posterior margins; epimeral plates with long setae on ventral margins; and uropod III inner ramus approx. one-third of outer ramus, both rami armed with simple setae. Gammarus mosuo Hou & Li, sp. n. can be distinguished from G. sinuolatus in the following characters ( G. sinuolatus in parentheses): antenna II calceoli absent (present); pereopods V–VII with long setae on anterior margin (with few setae on anterior margin); urosomites with two clusters of spines accompanied by setae (four groups of spines accompanied by long setae); and telson with a pair of short facial setae on each lobe (with long setae on dorsal surface).

The new species of Gammarus mosuo Hou & Li, sp. n. is similar to G. curvativus Hou & Li, 2003b in pereopods III and IV with long straight setae on posterior margins; uropod I with one basofacial spine; and uropod III inner ramus less than half of outer ramus, both rami densely with simple setae. Gammarus mosuo Hou & Li, sp. n. differs from G. curvativus Hou & Li, 2003b ( G. curvativus in parentheses) by eyes oval and small (reniform, and relatively large); antenna II calceoli absent (present); gnathopod II propodus with groups of long setae on anterior margin (with long curled setae on anterior margin); pereopods V–VII with long setae along anterior margin (with no long setae); and urosomites with two clusters of spines and setae on dorsal margins (with four groups of spines and setae).

The new species is similar to G. paucispinus Hou & Li, 2002b in eyes oval; antenna II calceoli absent; merus and carpus of pereopod III with clusters of long setae on posterior margins; and both rami of uropod III with simple setae. It differs from G. paucispinus Hou & Li, 2002b ( G. paucispinus in parentheses) by urosomite I with two clusters of spines and setae on dorsal margin (with a few short setae); telson 0.9 times as long as wide (0.8 times as long as wide); and each lobe with a pair of setae on surface (with two groups of long setae).