Gammarus vallecula 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 : 3-6

Gammarus vallecula Hou & Li sp. n. Figs 2, 3, 4, 5, 6, 7

Material examined.

Holotype: male (IZCAS-I-A1411-1), 8.5 mm, Liuba County (106.92°E, 33.61°N), altitude 1001 m, Hanzhong City, Shaanxi Province, China, October 23, 2013, collected by Yunchun Li and Jincheng Liu. Paratype: female (IZCAS-I-A1411-2), 7.8 mm, same data as holotype.

Etymology.

The specific name alludes to its typical biotope, living in a valley; adjective.

Diagnosis.

Antenna II with setae along peduncle articles and flagellum, calceoli absent; merus to propodus of pereopods III and IV with short straight setae on posterior margins; epimeral plate II with blunt posterodistal corner; epimeral plate III with subacute posterodistal corner; uropod III inner ramus reaching 0.5 times the length of outer ramus, second article of outer ramus subequal to adjacent spines, both rami with a few plumose setae on inner margins.

Description of holotype male

(IZCAS-I-A1411-1). 8.5 mm.

Head (Fig. 2A): eyes reniform, inferior antennal sinus deep, lateral cephalic lobe rounded.

Antenna I (Fig. 2B, C): peduncle articles I–III in length ratio 1.0: 0.7: 0.4, with distal setae; flagellum with 26 articles, articles IV–XX with aesthetascs; accessory flagellum with four articles; both primary and accessory flagella with short distal setae.

Antenna II (Fig. 2D): peduncle articles III–V in length ratio 1.0: 2.5: 2.3, peduncle article III with setae on lateral margin, articles IV and V of peduncle with clusters of lateral and medial setae; flagellum with ten articles, each article with long setae; calceoli absent.

Upper lip (Fig. 2E): ventral margin rounded, bearing short minute setae.

Mandible (Fig. 2G, 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: 3.1: 1.9, second article of palp with 12 marginal setae, article III with four A-setae, four B-setae, 16 D-setae, and five E-setae apically; incisor of right mandible with four teeth, lacinia mobilis bifurcate, with small teeth.

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

Maxilla I (Fig. 2I, J): asymmetrical, left inner plate with nine plumose setae and two simple setae on medial margin; outer plate with 11 robust serrated apical spines, each spine with small teeth; second article of left palp with seven slender spines apically; second article of right palp with five stout spines, one slender spine and one stiff spine.

Maxilla II (Fig. 2K): inner plate with three simple setae and 11 plumose facial setae in an oblique row; inner and outer plates with long setae apically.

Maxilliped (Fig. 2L): inner plate with three stout apical spines and one subapical spine, 21 plumose setae along lateral margin; outer plate bearing a row of 14 blade spines and three plumose setae apically; article IV of palp hooked, with a group of setae at hinge of unguis.

Pereon.Gnathopod I (Fig. 3A, B): coxal plate bearing three setae and two setae on anterior and posterior margins, respectively; basis with setae on anterior and posterior margins, and with three serrated spines accompanied by two setae on posterodistal corner; carpus 1.3 times as long as wide, 0.7 times as long as propodus, ventral margin bearing a cluster of simple setae and three clusters of serrated setae; propodus oval, palm with one medial spine and 12 spines on posterior margin and surface; dactylus with one seta on outer margin.

Gnathopod II (Fig. 3C, D): coxal plate bearing three setae and two setae on anterior and posterior margins, respectively; basis with setae on anterior and posterior margins, and with three serrated spines accompanied by one seta on posterodistal corner; carpus 1.8 times as long as wide, 0.9 times as long as propodus, bearing seven clusters of setae along ventral margin, two clusters of setae on dorsal margin; propodus subrectangular, palm margin with one medial spine and three spines on lateral posterodistal corner; dactylus with one seta on outer margin.

Pereopod III (Fig. 4A, B): coxal plate bearing two setae on anterior margin and three setae on posterior margin; basis elongated, with setae along anterior and posterior margins; merus with long and straight setae on posterior margin and two spines on anterior margin, anterodistal corner with one spine accompanied by setae; carpus with five spines accompanied by setae on posterior margin, anterodistal corner with one spine and one seta; propodus with three 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. 4C, D): coxal plate concave, bearing three setae on anterior margin and seven setae on posterior margin; basis with two setae on anterior margin, with clusters of setae on posterior margin; merus with clusters of long setae on posterior margin and one spine on anterior margin, anterodistal corner with one spine accompanied by setae; carpus with seven spines accompanied by setae on posterior margin, anterodistal corner with two spines accompanied by setae; propodus with two 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 V (Fig. 4E, F): coxal plate bearing one seta on anterior margin and three setae on posterior margin; basis expanded, with four long setae and three spines accompanied by fine setae on anterior margin, anterodistal corner with two spines accompanied by two setae, posterior margin with a row of 12 setae; merus with one spine accompanied by setae on anterior margin and one spine on posterior margin, anterodistal corner with two spines accompanied by setae and posterodistal corner with three spines; carpus with two groups of spines on anterior and posterior margins each; propodus with three groups of spines on anterior margin; dactylus with one plumose seta on posterior margin, and two setae at hinge of unguis.

Pereopod VI (Fig. 4G, H): coxal plate bearing two long setae and two fine setae on anterior and posterior margins, respectively; basis elongated, with two long setae and four spines accompanied by setae on anterior margin, anterodistal corner with three spines and one fine seta, posterior margin with a row of 12 fine setae; merus with three groups of spines and one spine on anterior and posterior margins, respectively, anterodistal and posterodistal corners with four spines each; carpus with three or two groups of spines on anterior and posterior margins, respectively; propodus with four groups of spines on anterior margin; dactylus with one plumose seta on posterior margin, and two setae at hinge of unguis.

Pereopod VII (Fig. 4I, J): coxal plate bearing one seta on anterior margin and five setae on posterior margin; basis with four long setae and four spines accompanied by setae on anterior margin, anterodistal corner with two spines and a fine seta, posterior margin with a row of 11 setae, posterodistal corner with one spine; merus with two groups of spines on anterior margin and one spine on posterior margin, anterodistal and posterodistal corners with four and three spines, respectively; carpus with three groups of spines on anterior margin and one spine on posterior margin, anterodistal and posterodistal corners with three and four spines, respectively; 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 gills of pereopods III–V longer than bases; gill of pereopod VI a little shorter than basis; gill of pereopod VII smallest, half the length of basis.

Pleon.Epimeral plates (Fig. 4 K–M): plate I ventrally rounded, bearing seven long setae on anteroventral margin and three tiny setae on posterior margin; plate II with two spines on ventral margin and six tiny setae on posterior margin, posterodistal corner blunt; plate III with three spines on ventral margin and six tiny setae on posterior margin, posterodistal corner subacute.

Pleopods I–III (Fig. 5 A–C): similar, peduncle with two retinacula accompanied by two setae; outer ramus slightly longer than inner ramus, both inner and outer rami fringed with plumose setae.

Urosome.Urosomites (Fig. 2M): urosomite I with one-one-one-one spines accompanied by setae on dorsal margin; urosomite II with three-one-one-three spines accompanied by setae on dorsal margin; urosomite III with two spines accompanied by two setae on each side and two pairs of setae on dorsal margin.

Uropods I–III (Fig. 5 D–F): uropod I peduncle with one basofacial spine, two spines on inner margin and three spines on outer margin, inner and outer distal corners with one and two spines, respectively; inner and outer rami with two and one spines on inner margins, respectively; both rami with five terminal spines. Uropod II peduncle with one and two spines on inner and outer margins respectively, and with one distal spine on each corner; inner ramus with two spines on inner margin; outer ramus with one spine on inner margin; both rami with five terminal spines. Uropod III peduncle with two spines accompanied by one seta on surface and eight distal spines; inner ramus 1.2 times as long as peduncle, reaching 0.5 times the length of outer ramus, with one spine accompanied by three plumose setae on inner margin and two distal spines accompanied by setae; proximal article of outer ramus with three pairs of spines accompanied by simple setae on outer margin, with four plumose setae and one simple seta on inner margin, terminal article with simple setae, subequal to adjacent spines.

Telson (Fig. 5G): deeply cleft, 0.8 times as long as wide; each lobe with one spine accompanied by one seta and clusters of setae on surface, bearing two distal spines accompanied by three setae.

Description of paratype female

(IZCAS-I-A1411-2). 7.8 mm.

Pereon.Gnathopod I (Fig. 6A, B): coxal plate bearing four and two setae on anterior and posterior margins, respectively; basis with long setae on anterior and posterior margins, posterodistal corner with four serrated spines accompanied by setae; propodus oval, palm with six spines on posterior margin, bearing long setae along anterior and posterior margins; dactylus with one seta on outer margin.

Gnathopod II (Fig. 6C, D): coxal plate bearing five and two fine setae 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.

Pereopods III–VII (Fig. 7 E–I): similar to those of male.

Oostegite (Fig. 6 H–K): oostegite of gnathopod II broad, oostegites of pereopods III and IV elongated, oostegite of pereopod V smallest.

Urosome.Uropods I–III (Figs 5H; 7J, K): 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; outer ramus with two spines on inner margin and one spine on outer margin; inner ramus with two spines on inner margin; both rami with five terminal spines. Uropod II short, peduncle bearing two spines on outer and inner margins each, with one spine on outer and inner distal corners each; outer ramus with one spine on outer margin; inner ramus with two spines on inner margin; both rami with five terminal spines. Uropod III peduncle with two spines accompanied by one seta on surface and five distal spines; inner ramus 1.1 times as long as peduncle, reaching 0.6 times the length of outer ramus, with one spine accompanied by three plumose setae and one simple seta on inner margin and two distal spines accompanied by setae; proximal article of outer ramus with five spines accompanied by one plumose seta and simple setae on outer margin, inner margin with three plumose setae and two simple setae, terminal article subequal to adjacent spines.

Telson (Fig. 7L): cleft, 0.8 times as long as wide; left lobe with one spine accompanied by one seta and a cluster of two setae on surface, bearing two distal spines accompanied by three setae; right lobe with one spine accompanied by one seta and a cluster of three setae on surface, bearing one distal spine accompanied by five setae.

Habitat.

This species was collected from a valley of south part of the Qinling. Individuals inhabit a stream, usually under decomposing leaves.

Remarks.

The new species of Gammarus vallecula Hou & Li, sp. n. is similar to G. craspedotrichus Hou & Li, 2002a in antenna II calceoli absent; pereopods III and IV with straight setae on posterior margins; and both rami of uropod III with plumose setae on inner margins. It differs from G. craspedotrichus ( G. craspedotrichus in parentheses) by peduncle of antenna II with setae along ventral margin, setae as long as article’s diameter (antenna II with long setae along ventral margin, setae as long as three times of article’s diameter); uropod I peduncle with one basofacial spine (without basofacial spine); inner ramus of uropod III 0.5 times the length of outer ramus (as long as first article of outer ramus); terminal article of outer ramus of uropod III subequal to adjacent spines (shorter); and urosomites I–III with four clusters of dorsal spines and setae (with two clusters of dorsal spines and setae).

Gammarus vallecula Hou & Li, sp. n. is also similar to G. emeiensis Hou, Li & Koenemann, 2002 in antenna II calceoli absent; epimeral plate II with blunt posterodistal corner and plate III with subacute posterodistal corner; peduncle of uropod I with one basofacial spine; and terminal article of outer ramus of uropod III approx. as long as adjacent spines of first article. It can be distinguished from G. emeiensis by the following characters ( G. emeiensis in parentheses): second article of left palp of maxilla I with seven slender spines apically (seven slender spines and three stiff setae); pereopod III with short setae on posterior margin (with long setae on posterior margin); and inner ramus of uropod III 0.5 times the length of outer ramus (0.74 times the length of first article of outer ramus).

The new species of Gammarus vallecula Hou & Li, sp. n. can be distinguished from G. martensi Hou & Li, 2004a which was collected on the summit of the Qinling by the following characters ( G. martensi in parentheses): antenna II flagellum with a few setae, calceoli absent (with flag-like brush of setae, calceoli present); merus and carpus of pereopods V–VII with few marginal setae (with marginal setae); and uropod III inner ramus approx. half of outer ramus, both with a few plumose setae on inner margins (inner ramus 0.75 times as long as outer ramus, both rami densely with plumose setae on inner and outer margins).