Gammarus jidutanxian 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 : 15-20

Gammarus jidutanxian Hou & Li sp. n. Figs 21, 22, 23, 24, 25, 26

Material examined.

Holotype: male (IZCAS-I-A1439-1), 8.2 mm, Langao County (108.91°E, 32.29°N), altitude 529 m, Ankang City, Shaanxi Province, China, October 28, 2013, collected by Yunchun Li and Jincheng Liu. Paratype: female (IZCAS-I-A1439-2), 9.8 mm, same data as holotype. Paratype: male (IZCAS-I-A1804), 8.5 mm, Huiwan Town (109.84°E, 32.15°N), Zhuxi County, Shiyan City, Hubei Province, August 28, 2015, collected by Chunjiang Sang.

Etymology.

The species name is a Chinese phrase, " jidutanxian ", meaning "adventure exploration", in honour of Mr. Chunjiang Sang extensively exploring karst biota in southern China; noun in apposition.

Diagnosis.

Antenna II peduncle with long setae, calceoli absent; epimeral plate III with subacute posterodistal corner; uropod III inner ramus reaching 0.6 times the length of outer ramus, outer ramus with no plumose setae on outer margin, terminal article of outer ramus shorter than adjacent spines; each lobe of telson with plumose setae on surface.

Description of holotype male

(IZCAS-I-A1439-1). 8.2 mm.

Head (Fig. 21A): eyes oval, inferior antennal sinus deep, lateral cephalic lobe rounded.

Antenna I (Fig. 21B, C): peduncle articles I–III in length ratio 1.0: 0.7: 0.4, with distal setae; flagellum with 30 articles, articles VII–XXV with aesthetascs; accessory flagellum with four articles; both primary and accessory flagella with short distal setae.

Antenna II (Fig. 21D): peduncle articles III–V in length ratio 1.0: 2.7: 2.3, articles IV–V with long setae along anterior and posterior margins; flagellum with 11 articles, each article with long setae; calceoli absent.

Upper lip (Fig. 21E): ventral margin rounded, bearing short minute setae.

Mandible (Fig. 21G, 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: 3.9: 2.5, second article with nine marginal setae, article III with four A-setae, eight B-setae, a row of D-setae, and five E-setae apically; incisor of right mandible with four teeth, lacinia mobilis bifurcate, with small teeth.

Lower lip (Fig. 21F): inner lobes lacking, outer lobes covered with thin setae.

Maxilla I (Figs 21I, J): asymmetrical, left inner plate with 13 plumose 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 four stout spines, one stiff seta and one slender spine.

Maxilla II (Fig. 21K): inner plate with 12 plumose setae in an oblique row; inner and outer plates with long setae apically.

Maxilliped (Fig. 21L): inner plate with three stout apical spines and one subapical spine, 15 plumose setae along lateral margin; outer plate bearing a row of 14 blade spines and four plumose setae apically; article IV of palp hooked, with three setae at hinge of unguis.

Pereon.Gnathopod I (Fig. 22A, B): coxal plate bearing four setae and two setae on anterior and posterior margins, respectively; basis with setae on anterior and posterior margins; carpus 1.4 times as long as wide, 0.8 times as long as propodus, posterior margin bearing four clusters of short setae; propodus oval, palm with one medial spine and 11 spines and clusters of simple setae on posterior margin and surface; dactylus with one seta on outer margin.

Gnathopod II (Fig. 22C, D): coxal plate bearing four setae and one seta on anterior and posterior margins, respectively; basis with setae on anterior and posterior margins; carpus 2.0 times as long as wide, approx. as long as propodus, bearing seven clusters of long setae along ventral margin, three clusters of setae on dorsal margin; propodus subrectangular, palm margin with one medial spine and four spines on posterodistal corner; dactylus with one seta on outer margin.

Pereopod III (Fig. 23A, B): coxal plate bearing three setae on anterior margin and one seta on posterior margin; basis elongated, with setae along anterior and posterior margins; merus with long straight setae on posterior margin and two spines accompanied by two setae on anterior margin, anterodistal corner with one spine accompanied by three setae; carpus with four clusters of spines accompanied by straight setae on posterior margin; propodus with three clusters 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. 23C, D): coxal plate concave, bearing four setae on anterior margin and six setae on posterior margin; basis with long setae along anterior and posterior margins; merus with clusters of setae on posterior margin and one spine accompanied by one seta on anterior margin, anterodistal corner with one spine accompanied by four setae; carpus and propodus with three groups of spines accompanied by setae on posterior margins; dactylus with one plumose seta on anterior margin, and two setae at hinge of unguis.

Pereopod V (Fig. 23E, F): coxal plate bearing one seta on anterior margin and two setae on posterior margin; basis with five setae and seven spines accompanied by fine setae on anterior margin, anterodistal corner with two spines accompanied by setae, posterior margin with a row of 14 setae; merus with two spines accompanied by setae on anterior margin and one spine accompanied by seta on posterior margin, anterodistal and posterodistal corners with one and two spines accompanied by setae respectively; carpus and propodus with groups of spines on anterior margins; dactylus with one plumose seta on posterior margin, and two setae at hinge of unguis.

Pereopod VI (Fig. 23G, H): coxal plate bearing one seta on posterior margin; basis with two setae and five spines accompanied by one seta on anterior margin, anterodistal corner with one spine and three fine setae, posterior margin with a row of 14 fine setae; merus to propodus with groups of spines accompanied by short setae on anterior margins; dactylus with one plumose seta on posterior margin, and two setae at hinge of unguis.

Pereopod VII (Fig. 23I, J): coxal plate bearing three setae on posterior margin; basis with two simple setae and five spines on anterior margin, anterodistal corner with two spines accompanied by fine setae, posterior margin with a row of 15 setae, and with one spine on inner surface; merus to propodus with groups of spines accompanied by short setae on anterior margins; dactylus with one plumose seta on posterior margin, and two setae at hinge of unguis.

Coxal gills: coxal gills of gnathopod II and pereopod III a little shorter than bases; gill of pereopod IV longer than basis; gills of pereopods V and VI shorter than bases; gill of pereopod VII smallest, less than half the length of basis.

Pleon.Epimeral plates (Fig. 22 E–G): plate I ventrally rounded, bearing three setae and one spine on anteroventral margin and four setae on posterior margin; plate II with one seta and two spines on ventral margin and six setae on posterior margin, posterodistal corner blunt; plate III with two spines on ventral margin and five setae on posterior margin, posterodistal corner subacute.

Pleopods I–III (Fig. 24 A–C): similar, peduncle with two retinacula accompanied by one seta; outer ramus as long as inner ramus, both rami fringed with plumose setae.

Urosome.Urosomites (Fig. 21M): urosomites I and II with one-one-one-one spines accompanied by setae on dorsal margins; urosomite III with one spine accompanied by two setae on each side and two setae on dorsal margin.

Uropods I–III (Figs 24 D–F): uropod I peduncle with one basofacial spine, three and two spines on inner and outer margins, respectively, inner and outer distal corners with one and two spines, respectively; inner ramus with two spines on inner margin; outer ramus with two spines on inner and outer margins each; both rami with five terminal spines. Uropod II peduncle with two spines on inner margin and one spine on outer margin, and with one distal spine on each corner; inner ramus with two spines on inner margin; outer ramus with two spines on outer margin; both rami with five terminal spines. Uropod III peduncle with three setae on surface and six distal spines; inner ramus 1.2 times as long as peduncle, reaching 0.6 times the length of outer ramus, with two spines accompanied by seven plumose setae on inner margin, five plumose setae on outer 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 ten plumose setae on inner margin, terminal article with simple setae, shorter than adjacent spines.

Telson (Fig. 24G): deeply cleft, approx. as long as wide; each lobe with three simple setae and two plumose setae on surface, bearing two distal spines accompanied by setae.

Description of paratype female

(IZCAS-I-A1439-2). 9.8 mm.

Pereon.Gnathopod I (Fig. 25A, B): coxal plate bearing four and two setae on anterior and posterior margins, respectively; basis with setae on anterior and posterior margins; propodus oval, palm with seven spines on posterior margin, bearing long setae along anterior and posterior margins; dactylus with one seta on outer margin.

Gnathopod II (Fig. 25C, D): coxal plate bearing four and one seta on anterior and posterior margins, respectively; basis with setae on anterior and posterior margins; propodus subrectangular, palm margin with four spines on posterodistal corner, bearing long setae along anterior and posterior margins; dactylus with one seta on outer margin.

Pereopods III and IV (Fig. 26A, B): with fewer setae on posterior margins than those of male.

Pereopods V–VII (Fig. 26 C–E): similar to those of male.

Oostegite (Fig. 25 E–G): oostegite of gnathopod II broad, oostegites of pereopods III and IV elongated, oostegite of pereopod V smallest.

Urosome.Uropods I–III (Fig. 26 F–H): uropod I peduncle with one basofacial spine, with one and three spines on inner and outer margins, respectively, with one and two spines on inner and outer corners; inner ramus with two spines on inner margin; outer ramus with one and two spines on inner and outer margins, respectively; both rami with five terminal spines. Uropod II peduncle with one spine on inner and outer margins each, with one distal spine on each corner; inner ramus with two spines on inner margin; outer ramus with two spines on outer margin; both rami with five terminal spines. Uropod III peduncle with setae on surface and six distal spines; inner ramus 1.4 times as long as peduncle, reaching 0.8 times the length of outer ramus, with one spine accompanied by four plumose setae and one simple seta on inner margin and two plumose setae accompanied by one simple setae on outer margin; proximal article of outer ramus with a single spine and two pairs of spines accompanied by simple setae on outer margin, with five plumose setae and four simple setae on inner margin, terminal article shorter than adjacent spines.

Telson (Fig. 24H): cleft, approx. as long as wide; each lobe with three or two simple setae and two plumose setae on surface, bearing two distal spines accompanied by setae.

Habitat.

This species was collected along the shore of a brook, usually in gravel and decomposing leaves. The type locality is located in a valley of north part of Daba Mountain.

Remarks.

The new species of Gammarus jidutanxian Hou & Li, sp. n. is most similar to G. craspedotrichus Hou & Li, 2002 in antenna II with long setae along peduncular articles and calceoli absent; and outer margin of outer ramus in uropod III with simple setae. It differs from G. craspedotrichus ( G. craspedotrichus in parentheses) in peduncle of uropod I with one basofacial spine (without basofacial spine); inner ramus reaching 0.6 times of outer ramus in uropod III (inner ramus approx. as long as outer ramus); and urosomites with four groups of spines and setae (with two clusters of spines and setae).

The new species of Gammarus jidutanxian Hou & Li, sp. n. is most similar to G. vallecula Hou & Li, sp. n. in antenna II with long setae on peduncle margin and calceoli absent; pereopods III and IV with straight setae on posterior margin; and urosomites with four groups of spines and setae on dorsal margin. Gammarus jidutanxian Hou & Li, sp. n. can be distinguished from G. vallecula Hou & Li, sp. n. ( G. vallecula in parentheses) in uropod III inner ramus reaching 0.6 times the length of outer ramus, terminal article shorter than adjacent spines (inner ramus approx. half the length of outer ramus, terminal article subequal or longer than adjacent spines); and telson as long as wide, with no spines on surface (telson 0.8 times as long as wide, each lobe with one spine accompanied by setae on surface).

Gammarus jidutanxian Hou & Li, sp. n. differs from Gammarus accretus Hou & Li, 2002a ( G. accretus in parentheses) by urosomites I and II with one-one-one-one spines accompanied by setae on dorsal margins (with only one group of setae); uropod I peduncle with one basofacial spine (without basofacial spine); and inner ramus of uropod III 0.6 times the length of outer ramus (approx. the same length).