Gammarus limosus, Hou, Zhonge & Li, Shuqiang, 2018

Hou, Zhonge & Li, Shuqiang, 2018, Four new Gammarus species from Tibetan Plateau with a key to Tibetan freshwater gammarids (Crustacea, Amphipoda, Gammaridae), ZooKeys 747, pp. 1-40 : 12-16

Gammarus limosus sp. n. Figs 17, 18, 19, 20, 21, 22

Material examined.

Holotype: male (IZCAS-I-A0063-1), 8.6 mm, Baxoi County (30.2°N, 97.2°E), Tibet, altitude 4400 m, August 21, 2001, collected by Xianjin Peng. Paratype: female (IZCAS-I-A0063-2), 5.5 mm; paratypes: five males and five females (IZCAS-I-A0063-3), same data as holotype.

Etymology.

This specific name alludes to its living environment, living silt beside a polluted river; adjective.

Diagnosis. Antenna I accessory flagellum with three articles; antenna II calceoli present; pereopods III and IV with few setae on posterior margin; inner ramus of uropod III reaching 0.6 times the length of outer ramus, terminal article of outer ramus longer than adjacent spines, both inner and outer rami with few marginal setae.

Description of holotype male.

(IZCAS-I-A0063-1), 8.6 mm.

Head. (Fig. 17A): cephalic lateral lobe truncated, inferior antennal sinus deep, eyes ovate.

Antenna I (Fig. 18A): peduncle articles I–III in length ratio 1.0: 0.7: 0.4, each article with distal setae, article II with two groups of setae on inner face; primary flagellum with 21 articles, most with aesthetascs; accessory flagellum with three articles, the distal article tiny.

Antenna II (Fig. 19A): gland cone shorter than peduncle article III, article IV approximately as long as article V, both with two or three groups of short setae along anterior and posterior margins; flagellum with 12 articles, proximal six articles with calceoli.

Upper lip (Fig. 17E): convex, with minute setae.

Mandible (Fig. 17G, H, K): asymmetrical, left incisor with five teeth; lacinia mobilis with four teeth; spine row with nine plumose setae; second article of palp with ten setae on medial margin, third article 0.7 times the length of second article, with four A-setae on outer face, five B-setae on inner face, a row of 22 D-setae and four E-setae. Incisor of right mandible with four teeth; lacinia molibis bifurcate, with small teeth; molar with one long seta.

Lower lip (Fig. 17D): inner lobes lacking, outer lobes covered with thin setae.

Maxilla I (Fig. 17I, J): asymmetrical, left inner plate with 15 plumose setae on medial margin; outer plate with eleven serrated spines; second article of palp with seven slender spines. Second article of right palp broad, with five blunt spines and one stiff seta.

Maxilla II (Fig. 17L): inner plate with 14 plumose setae on inner face; inner and outer plates with apical setae.

Maxilliped (Fig. 17F): inner plate with three apical and one subapical spines, and 17 plumose setae; outer plate with 13 blade spines on medial margin and five apical plumose setae; palp with four articles, terminal article unguis-form.

Pereon. Gnathopod I (Fig. 18C, D): coxal plate weakly dilated distally, lower margin with short setae; basis with long setae on anterior and posterior margins; carpus triangular, posterior margin with setae; propodus oval, palm oblique, with one median spine, seven spines on posterior margin and seven spines on inner face; dactylus longer than half of posterior margin, with one seta on outer margin.

Gnathopod II (Fig. 18B, E): coxal plate slightly narrowing distally, with short setae on lower margin; basis with long setae on anterior and posterior margins; carpus a little shorter than propodus, with sub-parallel margins, bearing setae on posterior margin; propodus subrectangular, palm transverse, with one median spine and four spines on posterior corner; dactylus beyond the palm margin, with one seta on outer margin.

Pereopod III (Fig. 19B, G): coxal plate with one seta on anterodistal and posterodistal corners each; basis with long setae on anterior and posterior margins; merus to propodus with few setae on posterior margin; merus with two spines on anterior margin and three clusters of setae on posterior margins; carpus and propodus with three groups of spines accompanied by setae on posterior margins; dactylus with one plumose seta on anterior margin and one simple and one stiff setae at hinge of unguis.

Pereopod IV (Fig. 19C, H): coxal plate concave, with one seta on anterior corner and five setae on posterior margin; basis with long setae on posterior margin; merus with one spine on anterior margin, posterior margin with two pairs of setae; carpus and propodus with two to four groups of spines accompanied by setae on posterior margins; dactylus with one plumose seta on anterior margin and a seta at hinge of unguis.

Pereopod V (Fig. 19D, I): coxal plate with one seta on anterior lobe and three setae on posterior lobe; basis nearly straight on posterior margin, with three setae and four spines on anterior margin, anterodistal corner with two spines accompanied by setae; posterior margin with a row of nine setae; merus and carpus with two groups of spines accompanied with few setae on anterior margins and one group of spines on posterior margins; propo dus with three groups of spines on anterior margin and a pair of setae on posterior margin; dactylus with one plumose seta on posterior margin and two setae at hinge of unguis.

Pereopod VI (Fig. 19E, J): coxal plate with two setae on posterior margin; basis elongated, anterior margin with four setae and four spines on anterior margin, anterodistal corner with one spine, posterior margin with a row of eight setae; merus and carpus with two groups of spines on anterior margins and a group of spines on posterior margins; propodus with three groups of spines on anterior margin and a seta on posterior margin; dactylus with two setae at hinge of unguis.

Pereopod VII (Fig. 19F, K): coxal plate with four setae on posterior margin; basis elongated, with five setae and four spines on anterior margin, anterodistal corner with two spines; posterior margin with a row of ten setae; merus and carpus with one or two groups of spines on anterior margins, and two or one spine on posterior margins; propodus with three groups of spines on anterior margin and a seta on posterior margin; dactylus with one seta at hinge of unguis.

Coxal gills (Figs 18B, 19B, C, E, F): present on gnathopod II and pereopods III–VII, sac-like.

Pleon. Epimeral plates (Fig. 17B): plate I ventrally rounded, with six setae on anteroventral margin and two setae on posterior margin; plate II with two spines on ventral margin, posterior margin blunt, with one seta; plate III with two spines on ventral margin, posterior margin acute, with two setae.

Pleopods (Fig. 18 F–H): subequal, peduncle with some long setae, bearing two retinacula accompanied by two setae; rami with approximately 18 segments, fringed with plumose setae.

Urosome. Urosomites (Fig. 17C): non-humped, urosomite I with two-one-one-two spines on dorsal margin; urosomite II with three-one-one-two spines on dorsal margin; urosomite III with two and one spine on lateral margins respectively, and two setae on dorsal margin.

Uropod I (Fig. 20D): peduncle with one basofacial spine, outer margin with one spine on outer margin, two spines on outer distal corner, one spine on inner margin, and one spine on inner distal corner; outer ramus with one spine on inner and outer margins each; inner ramus with one mid-lateral spine, both inner and outer rami with five distal spines.

Uropod II (Fig. 20E): peduncle with one spine on outer margin, and one spine on outer and inner corners each; outer ramus with one spine on outer margin; inner ramus with one spine on inner margin, both rami with five distal spines.

Uropod III (Fig. 20G): peduncle with one marginal spine and three distal spines; inner ramus 0.6 times the length of outer ramus, with two marginal and two distal spines; proximal article of outer ramus with three pairs of spines on outer margin, one spine on inner margin and four distal spines; terminal article of outer ramus longer than adjacent spines; both rami with few marginal setae.

Telson (Fig. 20F): cleft, each with three or four distal spines accompanied by few short setae.

Description of paratype female.

(IZCAS-I-A0063-2), 5.5 mm.

Pereon. Gnathopod I (Fig. 21A, C): palm of propodus not oblique as that of male, with eight spines on posterior corner.

Gnathopod II (Fig. 21B, D): carpus approx. as long as propodus, propodus subrectangular, palm truncated, with four spines on posterior corner.

Pereopods III–VII (Fig. 22 A–J): similar to those of male. Pereopods III and IV with more setae on posterior margins; pereopods V–VII stouter, basis broader than those of male.

Oostegites (Figs 20A, B, 22B, C): progressively decreasing in size, with long marginal setae.

Urosome. Uropod III (Fig. 20C): stouter than that of male, inner ramus less than half the length of outer ramus; both rami with few setae.

Habitat.

This species was collected along a riverside with altitude 4400 m, water polluted.

Remarks.

Gammarus limosus sp. n. is similar to G. altus sp. n. in antenna II having calceoli; pereopod V having few setae on posterior margin; and bases of pereopods V–VII elongated. Gammarus limosus sp. n. can be distinguished from G. altus ( G. altus in parentheses) by pereopod III with few setae on posterior margin (merus with four groups of setae on posterior margin); epimeral plate III acute on posterodistal corner (blunt); and uropod III inner ramus longer than half of outer ramus length (inner ramus 0.3 times the length of outer ramus).

Gammarus limosus sp. n. is very similar to G. balcanicus Schäferna, 1922 (widespread in Europe). It differs from the latter by pereopods III–IV and uropod III having few setae; bases of pereopods VI and VII slender.

The species of the genus Gammarus recorded from the Tibetan Plateau can be classified into four groups based on morphological comparison: (1) G. lacustris group, is characterized by uropod III inner ramus longer than half of outer ramus length, both rami fringed with plumose setae, and includes five species: G. lacustris Sars, 1863, G. lasaensis Barnard & Dai, 1988, G. hongyuanensis Barnard & Dai, 1988, G. frigidus Hou & Li, 2004, and G. jaspidus Hou & Li, 2004; (2) cave species with no eyes, including G. abstrusus Hou, Platvoet & Li, 2006, and G. praecipuus Li, Hou & An, 2013; (3) G. sinuolatus Hou & Li, 2004 with long simple setae on uropod III; and (4) G. kangdingensis group is characterized by uropod III having a few simple or plumose setae, and includes G. emeiensis Hou, Li & Koenemann, 2002, G. sichuanensis Hou, Li & Zheng, 2002, G. glaber Hou, 2017, Gammarus altus sp. n., G. kangdingensis sp. n., G. gonggaensis sp. n., and G. limosus sp. n. A key to these species is presented as follows.