Gammarus hoboksar Tong & Wang & Liu & Li & Hou 2022, sp. nov.

Gammarus hoboksar Hou, sp. nov.

( Figs 2–6)

Material examined. Holotype: male (IZCAS-I-A1354-1), 9.0 mm, a reservoir (85.806°E, 46.799°N), altitude 1320 m, Hoboksar Mongol Autonomous County, Xinjiang, China, July 29, 2013, collected by K. Meng, Z. Yao, Z. Zhao and J. Liu. Paratypes: two males (IZCAS-I-A1354-2, 3), same date as the holotype. One male specimen was used for molecular analysis, and the sequences were submitted to GenBank (OM 720083 for 28S and OM 679216 for COI, respectively).

Etymology. The species name is a noun in apposition, derived from the type locality “Hoboksar” from Mongolian language.

Diagnosis. Calceoli of antenna II absent; merus and carpus of pereopods III–IV with short setae; bases of pereopods V–VII each with setae on anterior margin; epimeral plates II–III each with subacute posterodistal corner; inner ramus of uropod III about 0.79 times the length of outer ramus, terminal article of outer ramus about 0.24 times the length of first article, both rami with simple setae and plumose setae; telson cleft, with spines and setae on surface and three spines on distal end.

Description of male. Based on holotype (IZCAS-I-A1354-1), 9.0 mm (Fig. 2).

Head (Fig. 3A): Eyes oval. Antenna I (Fig. 6A): longer than antenna II, peduncle articles 1–3 in length ratio 1.0: 0.5: 0.3, with distal setae; flagellum with 22 articles; accessory flagellum with four articles; both primary and accessory flagella with short distal setae. Antenna II (Fig. 6B): peduncle articles 3–5 in length ratio 1.0: 3.1: 3.0; flagellum with 11 articles, last article tiny, each article with distal setae, calceoli lacking. Upper lip (Fig. 3B): ventral margin rounded, bearing minute setae. Mandible (Fig. 3D, E): asymmetrical. Left mandible incisor with five teeth; lacinia mobilis with four teeth; molar well developed and with a plumose seta; palp composed of three articles, second article with nine setae on inner margin, third article with four A-setae on outer margin, four E-setae on apical margin. Right mandible incisor with three teeth and one small spine, lacinia mobilis bifurcate. Lower lip (Fig. 3C): inner lobes indistinct, outer lobes covered with fine setae. Maxilla I (Fig. 3F): inner plate with 17 plumose setae on medial margin; outer plate with 11 serrate spines; palp biarticulate, distal article with seven stiff spines and two slender setae. Maxilla II (Fig. 3G): inner plate narrower and shorter than outer plate, with a row of plumose setae on medial margin; outer plate with long apical setae and a tiny spine. Maxilliped (Fig. 3H): inner plate with three stout apical spines and one subapical spine; outer plate with a row of blade spines and five plumose apical setae; palp with four articles, terminal article hooked.

Pereon. Gnathopod I (Fig. 4A, B): coxal plate with two setae and one seta on anterior and posterior margins, respectively; basis anterior and posterior margins with long setae; merus with setae on posterodistal corner; carpus about 1.3 times as long as wide, about 0.6 times as long as propodus, anterior and posterior margins with setae; 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. 4C, D): coxal plate with two setae and one seta on anterior and posterior margins, respectively; basis anterior and posterior margins with long setae; merus with setae on posterodistal corner; carpus about 1.5 times as long as wide, about 0.9 times as long as propodus, with clusters of setae along ventral margin; propodus subrectangular, palm with one medial spine and four spines on posterodistal corner; dactylus with one seta on outer margin.

Pereopods III–VII (Fig. 5A, C, E, G, I), pereopod III (Fig. 5A, B): coxal plate with two setae and one seta on anterior and posterior margins, respectively; basis elongate, with two spines and setae on anterior margin, with clusters of setae on posterior margin; merus with one spine accompanied by one seta on anterior margin and three spines on anterodistal corner, posterior margin with groups of setae; carpus with groups of spines accompanied by setae on posterior margin and one spine on anterodistal corner; 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. 5C, D): shorter than pereopod III; coxal plate with one seta and two setae on anterior and posterior margins, respectively; basis with clusters of setae on posterior margin; merus with one spine on anterior margin and two spines on anterodistal corner, posterior margin with groups of setae; carpus and propodus with groups of spines accompanied by setae on posterior margin; dactylus with one plumose seta on anterior margin, and two setae at hinge of unguis. Pereopod V (Fig. 5E, F): coxal plate with one seta and two setae on anterior and posterior margins, respectively; basis expanded, with setae and five spines on anterior margin, anterodistal corner with one spine and one fine seta, posterior margin with a row of 11 setae; merus with three spines accompanied by fine setae on anterior margin and one spine on posterior margin, anterodistal and posterodistal corners with spines; carpus and propodus with groups of spines on anterior margin; dactylus with one plumose seta on posterior margin, and two setae at hinge of unguis. Pereopod VI (Fig. 5G, H): coxal plate with two setae on posterior margin; basis elongate, with three long setae and four spines on anterior margin, anterodistal corner with two spines and one fine seta, posterior margin with a row of 11 setae; merus with three spines accompanied by fine setae on anterior margin and a group of spines on posterior margin, anterodistal and posterodistal corners with three and four spines accompanied by setae, respectively; carpus and propodus with groups of spines on anterior margin; dactylus with one plumose seta on posterior margin, and two setae at hinge of unguis. Pereopod VII (Fig. 5I, J): coxal plate with four setae on posterior margin; basis elongate, with three long setae and two spines on anterior margin, anterodistal corner with two spines, posterior margin with a row of 13 setae; merus with two groups of spines on anterior margin and a pair of spines on posterior margin, anterodistal and posterodistal corners with four and six spines respectively; carpus and propodus with groups of spines on anterior margin; dactylus with one plumose seta on posterior margin, and two setae at hinge of unguis.

Coxal gills: coxal gills of pereopods III and IV about as long as bases; gills of gnathopod II and pereopod V longer than bases; gills of pereopods VI and VII much shorter than bases.

Pleon. Epimeral plates (Fig. 6H–J): plate I ventrally rounded, with three setae on anteroventral margin and two setae on posterior margin; plate II with four spines on ventral submargin and four setae on posterior margin, posterodistal corner subacute; plate III with two setae on anteroventral margin and three spines on ventral margin, posterior margin with four setae, posterodistal corner subacute.

Pleopods I–III (Fig. 6C): similar, outer ramus subequal to inner ramus, both rami fringed with plumose setae.

Urosome. Urosomites (Fig. 3I): urosomites I–II with four groups of one or three spines accompanied by fine setae on dorsal margins; urosomite III with two pairs of spines accompanied by fine setae and two fine setae on dorsal margin.

Uropods I–III (Fig. 6D–F): uropod I peduncle with one basofacial spine, with two spines on inner and outer margins, respectively, and with one and two spines on inner and outer distal corners; inner ramus with two marginal and four terminal spines; outer ramus with one marginal and five terminal spines. Uropod II short, peduncle with two spines on inner and outer margins, respectively, and one distal spine on each corner; inner ramus with two marginal and five terminal spines; outer ramus shorter than inner ramus, with one marginal and four terminal spines. Uropod III peduncle with two spines on surface and seven distal spines; inner ramus about 1.8 times as long as peduncle, reaching about 0.79 times the length of outer ramus, with three clusters of simple and plumose setae on inner margin, five groups of spines accompanied by plumose setae on outer margin; first article of outer ramus with plumose and simple setae on inner margin, three groups of spines accompanied by simple setae on outer margin, terminal article about 0.24 times as long as first article, with simple setae, longer than adjacent spines.

Telson (Fig. 6G): cleft, 1.1 times as long as wide; left lobe with two spines accompanied by one seta on surface; right lobe with one spine accompanied by one seta and three setae on surface; each lobe with three distal spines accompanied by setae.

Female unknown.

Variations. Right mandible incisor with four teeth or three normal teeth and one small spine. Uropod III inner ramus with three to five clusters of simple and plumose setae on inner margin, two to five groups of spines accompanied by plumose setae on outer margin; first article of outer ramus with three or four groups of spines accompanied by simple setae on outer margin; Urosomite III with two or four groups of spines accompanied by fine setae on dorsal margin.

Remarks: Gammarus hoboksar Hou, sp. nov. is closely related to G. takesensis in accessory flagellum with four articles, pereopods III and IV each with short setae on posterior margin, and epimeral plates II–III with subacute corner. The new species can be distinguished from G. takesensis by the following characters (G. takesensis in parentheses): (1) calceoli lacking (present); (2) inner ramus of uropod III about 0.79 times the length of outer ramus (0.65 times the length of outer ramus); terminal article of the outer ramus of uropod 3 about 0.24 times the length of first article (0.13 times the length of first article); and (3) both lobes of telson with spines and setae on surface (only with setae).

Gammarus hoboksar Hou, sp. nov. is similar to G. tastiensis in the shape of gnathopods I–II, merus and carpus of pereopods III–IV with short setae, and uropod III both rumi with long plusome setae. It can be distinguished from G. tastiensis by the following characters (G. tastiensis in parentheses): (1) calceoli lacking (present); peduncle of antenna II with long setae (relatively short); (2) inner ramus of uropod III about 0.79 times the length of outer ramus (0.66 times); terminal article about 0.24 times the length of first article (0.16 times); and (3) right lobe of telson with one spine and setae on surface (only with setae) and three distal spines (two).

Distinguishing features of all the nine species of genus Gammarus from Xinjiang can be found in the key below.