Gammarus altus, 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 : 3-5

Gammarus altus sp. n. Figs 2, 3, 4, 5, 6

Material examined.

Holotype: male (IZCAS-I-A0061-1), 11.6 mm, Maniganggo Town (31.9°N, 99.2°E), Dege County, Sichuan Province, altitude 4000 m, August 12, 2001, collected by Xianjin Peng. Paratype: female (IZCAS-I-A0061-2), 10.1 mm; paratypes: five males and five females (IZCAS-I-A0061-3), same data as holotype.

Etymology.

The specific name alludes to its typical biotope, living in high altitude; adjective.

Diagnosis.

Pereopods III and IV with a few setae on posterior margins; pereopods V–VII slender, bases elongated, carpus and propodus with spines on anterior margins but few setae; epimeral plates with blunt posterodistal corners; uropod III inner ramus length approx. one-third of outer ramus length, both rami with marginal spines but with few marginal setae.

Description of male holotype.

(IZCAS-I-A0061-1), 11.6 mm.

Head. (Fig. 4D): cephalic lateral lobe truncated, inferior antennal sinus deep, eyes ovate.

Antenna I (Fig. 4A): peduncle articles I–III in length ratio 1.0: 0.7: 0.4, with some setae on posterior margin; primary flagellum with 28 articles, most with aesthetascs, accessory flagellum with three articles.

Antenna II (Fig. 4B): gland cone reaching peduncle article III, article IV a little shorter than article V, bearing one to three clusters of setae on lateral and medial margins; flagellum with ten articles, proximal seven articles with calceoli.

Upper lip (Fig. 2C): convex, with minute setae.

Mandible (Fig. 2A, B, H): incisor of left mandible with five teeth; lacinia mobilis with four teeth; spine row with six plumose setae; second article of palp with 15 marginal setae and four medial setae, third article 83% length of second article, with six A-setae on outer face, two groups of B-setae on inner face, approx. 17 D-setae and four E-setae apically. Incisor of right mandible with four teeth; lacinia mobilis bifurcate, with small teeth.

Lower lip (Fig. 2D): inner lobes lacking, outer lobes covered with thin setae.

Maxilla I (Fig. 2F, G): asymmetrical, left inner plate with 18 plumose setae; outer plate with eleven serrated apical spines; second article of left palp with seven slender spines and two stiff setae; second article of right palp with five blunt spines and one stiff seta.

Maxilla II (Fig. 2E): inner plate with 16 plumose setae in an oblique row; inner and outer plates with long setae apically.

Maxilliped (Fig. 2I): inner plate with three apical spines and 12 plumose marginal setae; outer plate with a row of 14 blade spines on medial margin and four plumose setae apically; third article of palp with long setae, terminal article hooked, with a group of setae at hinge of unguis.

Pereon. Gnathopod I (Fig. 3A, B): coxal plate bearing a seta on anterior and posterior corners each; basis with long setae on anterior and posterior margins; carpus sub-parallel, 71% length of propodus, posterior margin with groups of setae; propodus pyriform, palm oblique, with one medial spine, seven spines on posterior margin and six spines on inner face; dactylus more than half of posterior margin in length, with one seta on outer margin.

Gnathopod II (Fig. 3C, D): coxal plate with two setae on anterior corner and one seta on posterior corner; basis with setae on anterior and posterior margins; carpus almost as long as propodus, with subparallel margins, bearing seven clusters of setae along ventral margin, a group of setae on dorsal margin; propodus subrectangular, palm transverse, with one medial spine and four spines on posterior corner; dactylus beyond the palm margin, with one seta on outer margin.

Pereopod III (Fig. 4F, G): coxal plate with two setae and one seta on anterior and posterior margins, respectively; basis with setae along anterior and posterior margins; merus with two spines on anterior margin and four clusters of setae on posterior margin, anterodistal corner with one spine accompanied by setae; carpus with three groups of spines accompanied by setae on posterior margin, anterodistal corner with one spine and posterodistal corner with two spines accompanied by setae; propodus with four groups of spines accompanied by setae on posterior margin, and two spines on posterodistal corner; dactylus stout, with one plumose seta on anterior margin and one seta at joint of unguis.

Pereopod IV (Fig. 4E, H): coxal plate concave posteriorly, with two setae on anterior corner and six setae on posterior margin; basis with one spine on anterodistal corner, and clusters of setae on posterior margin; merus with a spine on anterior margin, a spine accompanied with setae on anterodistal corner, three clusters of short setae on posterior margin; carpus and propodus with groups of spines accompanied by a few setae on posterior margins; dactylus with one plumose seta on anterior margin, and two setae at hinge of unguis.

Pereopod V (Fig. 5A): coxal plate with one seta on anterior lobe and four setae on posterior margin; basis posterior margin nearly straight, with four spines on anterior margin and one spine on anterodistal corner, and a row of 13 setae on posterior margin; merus with two spines on anterior margin and two spines on posterior margin, anterodistal and posterodistal corners with two spines each; carpus and propodus with groups of spines accompanied by fine setae on anterior margin, posterior margin of carpus with three groups of spines accompanied with setae; dactylus with two setae at hinge of unguis.

Pereopod VI (Fig. 5C, G): coxal plate with one seta and three setae on anterior and posterior margins, respectively; basis elongated, with one long seta and four spines on anterior margin, anterodistal corner with one spine accompanied by setae; posterior margin narrowing distally, with a row of 14 fine setae; merus with two groups of spines on anterior margin and two spines on posterior margin, anterodistal and posterodistal corners with two spines each; carpus and propodus with groups of spines on anterior margin, posterior margin of carpus with two pairs of spines accompanied by setae; dactylus with one seta at hinge of unguis.

Pereopod VII (Fig. 5B, H): coxal plate with five setae on posterior margin; basis expanded, with two long setae and four spines on anterior margin, anterodistal corner with two spines accompanied by setae, posterior margin with a row of 15 setae, and a spine on inner surface; merus with two pairs of spines on anterior margin and two single spines on posterior margin, anterodistal and posterodistal corners with two spines each; carpus and propodus with three or four pairs of spines on anterior margins, posterior margin of carpus with two pairs of spines, and posterior margin of propodus with two clusters of setae; dactylus with one plumose seta on posterior margin and two setae at hinge of unguis.

Coxal gills (Figs 3D, 4E, F, 5 A–C): present on gnathopod II and pereopods III–VII, sac-like.

Pleon. Epimeral plates (Fig. 4C): plates I–III truncated to weakly acute, bearing two short setae on posterior margins. Plate I ventrally rounded, with nine setae on ventral margin; plate II with one spine on ventral margin; plate III with two spines on ventral margin.

Pleopods (Fig. 5 D–F): subequal in length, peduncle with some marginal setae and two retinacula accompanied by two setae; inner and outer rami with approximately 20 segments, armed with plumose setae.

Urosome. Urosomites (Fig. 6E): non-humped, urosomites I–II bearing two-one-one-two spines on dorsal margin; urosomite III with two-one spines on lateral margins and two setae on dorsal margin.

Uropod I (Fig. 6C): peduncle longer than rami, with one basofacial spine, one spine on outer margin and two spines on inner margin, two spines and one spine on outer and inner distal corners respectively; 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 (Fig. 6A): peduncle with one spine on outer margin and one spine on outer distal corner; inner ramus with one spine on inner margin; outer ramus with one spine on outer margin, both rami with five terminal spines.

Uropod III (Fig. 6D): peduncle with one marginal spine and some setae; inner ramus length nearly one-third of outer ramus length, with three spines accompanied by setae on inner margin, outer margin bare; proximal article of outer ramus slender, with four pairs of spines on outer margin, six groups of spines and setae on inner margin, and four distal spines, terminal article cone-shaped, with simple setae distally; both rami with few short setae.

Telson (Fig. 6B): cleft, each lobe with three distal spines, one basolateral spine and some facial setae.

Description of paratype female.

(IZCAS-I-A0061-2), 10.1mm.

Pereon. Gnathopod I (Fig. 6F): propodus of gnathopod I ovate, palm slant, with seven spines on posterior corner, dactylus with one seta on outer margin.

Gnathopod II (Fig. 6G): propodus subrectangular, with two spines on posterior corner.

Oostegite: present on gnathopod II and pereopods III–V.

Urosome. Uropod III (Fig. 6H): inner ramus less than 30% length of outer ramus, with two spines on inner ramus and one distal spine accompanied by setae; outer ramus with four or five groups of spines accompanied by setae on inner and outer margins; both rami armed with few marginal setae.

Habitat.

This species was collected from a stream with altitude 4000 m, water clear and cold. There are a few water plants in the locality.

Remarks.

Gammarus altus sp. n. is most similar to G. glaber Hou, 2017 in having some setae on posterior margins of pereopods III and IV, and uropod III inner ramus length around one-third of outer ramus length, both rami with spines but few setae. The new species can be distinguished from G. glaber by the following characters ( G. glaber in parentheses): second article of palp with two groups of B-setae (a group of B-setae); bases of pereopods V–VII elongated (broad), narrowing distally (posterior margin of pereopods V and VI nearly straight); uropod III with spines accompanied by simple setae on inner margin (uropod III with spines accompanied by plumose setae); and telson with no medial spines on surface (with one or two spines on medial surface).

This species is similar to G. sichuanensis Hou, Li & Zheng, 2002 in peduncle of antenna I and II with two or three groups of setae along anterior and posterior margins, and pereopod IV with a few setae on posterior margin. It differs from G. sichuanensis ( G. sichuanensis in parentheses) by pereopod III with short setae on posterior margins of merus and carpus (with long setae on posterior margins of merus and carpus); bases of pereopods V–VII elongated (broad in G. sichuanensis ); uropod III with no plumose setae (both rami with plumose setae on inner and outer margins).