Gammarus glaber Hou

Zhao, Shuangyan, Meng, Kaibaryer & Hou, Zhonge, 2017, Two new Gammarus species and a new name (Crustacea: Amphipoda: Gammaridae) from Northwest China, Zootaxa 4273 (2), pp. 195-215 : 205-214

Gammarus glaber Hou sp. nov.

Figs 8–13

Material examined. Holotype: male (IZCAS-I-A1394-1), 12.4 mm, Mengda alpine lake (102.68°E, 35.79°N), altitude 2491 m, Xunhua Salar Autonomous County, Haidong City, Qinghai Province, China, October 26, 2013, collected by Z. Zhao and Q. Zhao . Paratype: female (IZCAS-I-A1394-2), 8.1 mm; male (IZCAS-I-A1394-3), 15.3 mm, same data as holotype.

Etymology. The specific name is from Latin glaber (bare), in reference to the uropod III with few setae; adjective.

Diagnosis. Eyes reniform; epimeral plate II with blunt posterodistal corner; epimeral plate III with subacute posterodistal corner; inner ramus of uropod III subequal to peduncle, reaching 0.3 times the length of outer ramus; outer ramus of uropod III with spines accompanied by few simple and plumose setae on inner margin, second article of outer ramus elongate.

Description of male. Holotype (IZCAS-I-A1394-1), male 12.4 mm; paratype (IZCAS-I-A1394-3), male 15.3 mm, used for illustration of uropod II.

Head ( Fig. 8 A): Eyes reniform, inferior antennal sinus deep, lateral cephalic lobe nearly straight.

Antenna I ( Fig. 8 B, C): peduncle articles 1–3 in length ratio 1.0: 0.8: 0.4, with distal setae; flagellum with 27 articles, articles 4–25 with aesthetascs; accessory flagellum with four articles; both primary and accessory flagella with short distal setae.

Antenna II ( Fig. 8 D, E): peduncle articles 3–5 in length ratio 1.0: 2.6: 2.5, article 3 of peduncle with setae on posterior and anterior corners, articles 4–5 of peduncle with clusters of lateral and medial setae; flagellum with 12 articles, with setae along ventral margins; articles 2–4 with calceoli.

Upper lip ( Fig. 8 F): ventral margin rounded, bearing short minute setae.

Mandible ( Fig. 8 H, I): left mandible incisor with five teeth; lacinia mobilis with four teeth; spine row with five pairs of plumose setae; articles 1–3 of palp in length ratio 1.0: 3.1: 2.9, second article of palp with 12 marginal setae, article 3 with six A-setae, three B-setae, 20 D-setae and five E-setae apically; incisor of right mandible with four teeth, lacinia mobilis bifurcate, with small teeth.

Lower lip ( Fig. 8 G): inner lobes lacking, outer lobes covered with thin setae.

Maxilla I ( Fig. 8 J, K): asymmetrical, right inner plate with 14 plumose setae on medial margin; outer plate with 11 robust serrated apical spines; second article of right palp with four stout spines and two slender spines; second article of left palp with six slender spines apically.

Maxilla II ( Fig. 8 L): inner plate with 11 plumose facial setae in an oblique row; inner and outer plates with long setae apically.

Maxilliped ( Fig. 8 M): inner plate with three stout apical spines and one subapical spine, 15 plumose setae along lateral margin; outer plate bearing a row of blade spines and three plumose setae apically; article 4 of palp hooked, with a group of setae at hinge of unguis.

Gnathopod I ( Fig. 9 A, B): coxal plate bearing two setae and one seta on anterior and posterior margins, respectively; basis with setae on anterior and posterior margins; carpus about 1.3 times as long as wide, about 0.6 times as long as propodus, posterior margin bearing short setae; propodus oval, palm with one medial spine and 13 spines on posterior margin and surface; dactylus with one seta on outer margin.

Gnathopod II ( Fig. 9 C, D): coxal plate bearing three fine setae and one seta on anterior and posterior margins; basis with setae on anterior and posterior margins, posterodistal corner with short setae; carpus 1.7 times as long as wide, about 0.7 times as long as propodus, bearing six clusters of setae along ventral margin, two clusters of setae on dorsal margin; propodus subrectangular, palm margin with one medial spine and two spines on posterodistal corner; dactylus with one seta on outer margin.

Pereopod III ( Fig. 10 A, B): coxal plate bearing three setae on anterior margin; basis elongate, with setae along anterior and posterior margins; merus with six clusters of setae on posterior margin and two spines accompanied by setae on anterior margin, anterodistal corner with one spine accompanied by setae; carpus with spines accompanied by setae on posterior margin, anterodistal and posterodistal corners with one and two spines accompanied by setae, respectively; propodus with three groups 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. 10 C, D): coxal plate excavated, bearing three setae on anterior margin and five setae on posterior margin; basis with one spine accompanied by one seta on anterodistal corner, with clusters of setae on posterior margin; merus with clusters of short setae on posterior margin and two spines accompanied by fine setae on anterior margin, anterodistal corner with one spine accompanied by setae; carpus and propodus with groups of spines accompanied by fine setae on posterior margin; dactylus with one plumose seta on anterior margin, and two setae at hinge of unguis.

Pereopod V ( Fig. 10 E, F): coxal plate bearing four setae on posterior margin; basis expanded, with four spines accompanied by fine setae on anterior margin, anterodistal corner with three spines, posterior margin with a row of ten setae; merus with two spines accompanied by fine setae on anterior margin and two spines on posterior margin, anterodistal corner with one spine accompanied by setae and posterodistal corner with three spines; carpus with groups of spines on anterior and posterior margins, respectively; 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. 10 G, H): coxal plate bearing one seta and four setae on anterior and posterior margins, respectively; basis elongate, with two long setae and four spines on anterior margin, anterodistal corner with one spine and two fine setae, posterior margin with a row of 13 setae; merus with three groups of spines and two spines on anterior and posterior margins, respectively, anterodistal corner with two spines accompanied by setae and posterodistal corner with two 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 VII ( Fig. 10 I, J): coxal plate bearing one seta on anterior margin and five setae on posterior margin; basis with two simple setae and five spines on anterior margin, anterodistal corner with two spines and a fine seta, posterior margin with a row of 12 setae; merus with two groups of spines on anterior margin and two spines accompanied by fine setae on posterior margin, anterodistal and posterodistal corners with three and four 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 gill of gnathopod II and gill of pereopod IV a little longer than bases; gills of pereopods III, V and VI a little shorter than bases; gill of pereopod VII smallest, about half of basis.

Epimeral plates ( Fig. 13 A–C): plate I ventrally rounded, bearing four long setae and a tiny seta on anteroventral margin and three setae on posterior margin; plate II with three spines on ventral margin and four setae on posterior margin, posterodistal corner blunt; plate III with three spines on ventral margin and five setae on posterior margin, posterodistal corner subacute.

Pleopods I–III ( Fig. 11 B–D): similar, peduncle with two retinacula accompanied by one or two setae; outer ramus slightly shorter than inner ramus, both inner and outer rami fringed with plumose setae.

Urosomites ( Fig. 11 A): urosomite I with one-one-one-one spines accompanied by setae on dorsal margin; urosomite II with one-one-one-one spines on dorsal margin; urosomite III with two spines accompanied by two setae on each side.

Uropods I–III ( Fig. 11 E–G): uropod I peduncle with one basofacial spine, three spines on outer margin, with one and two spines on inner and outer distal corners, respectively; inner ramus with one spine on inner margin; outer ramus with one spine on inner and outer margins, respectively; both rami with five terminal spines. Uropod II (paratype), holotype damaged and replaced with another larger male; peduncle with one distal spine on each corner; both rami with one spine on inner margins respectively and five terminal spines. Uropod III peduncle with one spine accompanied by one seta and three setae on surface and four distal spines; both rami with few setae; inner ramus subequal to peduncle, reaching 0.3 times the length of outer ramus, with two spines accompanied by three setae on inner margin and one distal spine accompanied by setae; first article of outer ramus with four pairs of spines accompanied by simple setae on outer margin, with five groups of spines accompanied by simple and plumose setae on inner margin, terminal article with simple setae, longer than adjacent spines.

Telson ( Fig. 10 K): deeply cleft, as long as wide; left lobe with a pair of spines accompanied by one seta, a single spine and two setae on surface; right lobe with a pair of spines accompanied by one seta, two single spines and one seta on surface; each lobe bearing three distal spines accompanied by setae.

Description of female. Paratype (IZCAS-I-A1394-2), 8.1 mm.

Gnathopod I ( Fig. 12 A, B): coxal plate bearing two setae and one seta on anterior and posterior margins, respectively; basis with long setae on anterior and posterior margins, posterodistal corner with short setae; propodus oval, palm with three spines on posterior margin, bearing long setae along anterior and posterior margins; dactylus with one seta on outer margin, and two setae at hinge of unguis.

Gnathopod II ( Fig. 12 C, D): coxal plate bearing three setae and one seta on anterior and posterior margins, respectively; basis with setae on anterior and posterior margins; propodus subrectangular, palm margin with two robust spines and three slender spines on posterodistal corner, bearing long setae along anterior and posterior margins; dactylus with one seta on outer margin.

Pereopods III–VII ( Fig. 13 D–H): similar to those of male.

Uropods I–III ( Fig. 11 H–J): uropod I peduncle with one basofacial spine, with two and one spines on outer and inner margins, respectively, with two and one spines on outer and inner distal corners, respectively; both rami with one spine on inner margin respectively and five terminal spines. Uropod II short, peduncle bearing one spine on inner margin, with one spine on outer and inner distal corners, respectively; outer ramus with one spine on outer and inner margins, respectively; inner ramus with one spine on inner margin; both rami with five terminal spines. Uropod III peduncle with one spine on surface and five distal spines; both rami with few setae; inner ramus subequal to peduncle, reaching 0.3 times the length of outer ramus, with one distal spine accompanied by setae; first article of outer ramus with three pairs of spines accompanied by setae on outer margin, inner margin with five spines accompanied by plumose setae and simple setae, terminal article longer than adjacent spines.

Telson ( Fig. 13 I): cleft, sudequal to wide, each lobe with two spines accompanied by setae on surface, with three distal spines accompanied by setae.

Oostegite ( Fig. 12 E–H): oostegite of gnathopod II broad, with marginal setae, oostegites of pereopods III and IV elongate, oostegite of pereopod V smallest.

Habitat. This species was collected from a spring near the Mengda alpine lake.

Remarks. Gammarus glaber sp. nov. is most similar to G. brevipodus Hou et al., 2004 in pereopods III and IV with some short setae on posterior margins, and inner ramus of uropod III about 0.3 times of outer ramus, both rami with spines but few setae. The new species can be distinguished from G. brevipodus Hou et al., 2004 by the following characters ( G. brevipodus in parentheses): eyes reniform (relatively small); calceoli present (lacking); urosomites I and II with 1-1-1-1 spines accompanied by setae on dorsal margins (with three groups of spines accompanied by fine setae); outer ramus of uropod III with the terminal article much longer than adjacent spines (subequal), inner margin of first article of outer ramus with spines accompanied by simple and plumose setae (with spines accompanied by few setae); both lobes of telson with spines and setae on surface (only a seta on the left lobe).

This species differs from G. takesensis Hou et al., 2004 (character states in parentheses) by epimeral plate II with blunt posterodistal corner (slightly pointed); urosomites I and II with 1-1-1-1 spines accompanied by setae on dorsal margin, and urosomite III with two spines accompanied by two setae on each side (urosomites I–III with three groups of robust setae accompanied by fine setae); inner ramus of uropod III about 0.3 times the length of outer ramus (0.74 times of first article of outer ramus); first article of outer ramus of uropod III with spines accompanied by simple and plumose setae on inner margin (only with plumose setae); both lobes of telson with spines and setae on surface (setae).

The new species is similar to G. simplex sp. nov. in the shape of gnathopods I and II. It differs from G. simplex (character states in parentheses) by eyes reniform (oval); pereopods III and IV with setae shorter and fewer than those of G. simplex ; epimeral plate III with subacute posterodistal corner (blunt); urosomite I with spines and setae on dorsal margin (only with setae); urosomite II with 1-1-1-1 spines on dorsal margin (with two groups of spines accompanied by setae); inner ramus of uropod III about 0.3 times the length of outer ramus (0.5 times of outer ramus) and the terminal article of outer ramus longer than adjacent spines (shorter); both rami of uropod III with few setae (densely with simple setae); both lobes of telson with spines and setae on surface (setae).

Figures

FIGURE 8. Gammarus glaber sp. nov., holotype, male 12.4 mm. A, head; B, antenna I; C, aesthetascs of antenna I; D, antenna II; E, calceoli of antenna II; F, upper lip; G, lower lip; H, left mandible; I, incisor of right mandible; J, right maxilla I; K, palp of left maxilla I; L, maxilla II; M, maxilliped.

FIGURE 9. Gammarus glaber sp. nov., holotype, male 12.4 mm. A, gnathopod I; B, propodus of gnathopod I; C, gnathopod II; D, propodus of gnathopod II.

FIGURE 10. Gammarus glaber sp. nov., holotype, male 12.4 mm. A, pereopod III; B, dactylus of pereopod III; C, pereopod IV; D, dactylus of pereopod IV; E, pereopod V; F, dactylus of pereopod V; G, pereopod VI; H, dactylus of pereopod VI; I, pereopod VII; J, dactylus of pereopod VII; K, telson.

FIGURE 11. Gammarus glabrer sp. nov., holotype, male 12.4 mm, A – E, G; paratype, male 15.3 mm, F; paratype, female 8.1 mm, H – J. A, urosomites (dorsal view); B, pleopod I; C, pleopod II; D, pleopod III; E, uropod I; F, uropod II; G, uropod III; H, uropod I; I, uropod II; J, uropod III.

FIGURE 12. Gammarus glaber sp. nov., paratype, female 8.1 mm. A, gnathopod I; B, propodus of gnathopod I; C, gnathopod II; D, propodus of gnathopod II; E, oostegite of gnathopod II; F, oostegite of pereopod III; G, oostegite of pereopod IV; H, oostegite of pereopod V.

FIGURE 13. Gammarus glaber sp. nov., holotype, male 12.4 mm, A – C; paratype, female 8.1 mm, D – I. A, epimeral plate I; B, epimeral plate II; C, epimeral plate III; D, pereopod III; E, pereopod IV; F, pereopod V; G, pereopod VI; H, pereopod VII; I, telson.