Gammarus longdong 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 : 20-23

Gammarus longdong Hou & Li sp. n. Figs 27, 28, 29, 30, 31, 32

Material examined.

Holotype: male (IZCAS-I-A1566-1), 10.1 mm, Qinglong Cave (103.75°E, 27.69°N), altitude 1289 m, Mohan Town, Daguan County, Zhaotong City, Yunnan Province, China, March 18, 2014, collected by Yunchun Li and Jincheng Liu. Paratype: female (IZCAS-I-A1566-2), 7.3 mm, same data as holotype.

Etymology.

The species name is taken from the Chinese word, " longdong " meaning "Dragon Cave", referring to a cave filled with water; noun in apposition.

Diagnosis.

Peduncle of antenna II with long setae, calceoli absent; merus and carpus of pereopod III with clusters of long setae on posterior margins; epimeral plates II and III with subacute posterodistal corners; uropod I peduncle with no basofacial spine; inner ramus of uropod III reaching 0.9 times the length of outer ramus, terminal article vestigial.

Description of holotype male

(IZCAS-I-A1566-1). 10.1 mm.

Head (Fig. 27A): eyes reniform, inferior antennal sinus deep.

Antenna I (Fig. 27B, C): peduncle articles I–III in length ratio 1.0: 0.8: 0.4, with distal setae; flagellum with 31 articles, articles V–XXX with aesthetascs; accessory flagellum with four articles; both primary and accessory flagella with short distal setae.

Antenna II (Fig. 27D): peduncle articles III–V in length ratio 1.0: 2.9: 2.7, articles IV–V of peduncle with lateral and medial setae; flagellum with 11 articles, each article with long setae; calceoli absent.

Upper lip (Fig. 27E): ventral margin rounded, bearing short minute setae.

Mandible (Fig. 27G, H): left mandible incisor with five teeth; lacinia mobilis with four teeth; spine row with six pairs of plumose setae; articles I–III of palp in length ratio 1.0: 2.7: 2.0, second article with 15 marginal setae, article III with four A-setae, four 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. 27F): inner lobes lacking, outer lobes covered with thin setae.

Maxilla I (Fig. 27I, J): asymmetrical, left inner plate with 15 plumose setae on medial margin; outer plate with 11 robust serrated apical spines; second article of left palp with nine slender spines apically; second article of right palp with four stout spines, one stiff seta and one slender spine.

Maxilla II (Fig. 27K): inner plate with 12 plumose setae in an oblique row; inner and outer plates with long setae apically.

Maxilliped (Fig. 27L): inner plate with three stout apical spines, one subapical spine, and 20 plumose setae; outer plate bearing a row of 17 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. 28A, B): coxal plate bearing two setae and four setae on anterior and posterior margins, respectively; basis with setae on anterior and posterior margins; merus bearing setae on posterodistal corner; carpus 1.7 times as long as wide, 0.75 times as long as propodus, bearing four clusters of setae along ventral margin and two clusters of setae on dorsal margin; 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. 28C, D): coxal plate bearing two setae and three setae on anterior and posterior margins, respectively; basis with setae on anterior and posterior margins; merus bearing setae on posterodistal corner; carpus 1.9 times as long as wide, 0.8 times as long as propodus, bearing six clusters of setae along ventral margin and two 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. 29A, B): coxal plate bearing three setae and two setae on anterior and posterior margins, respectively; basis elongated, with setae along anterior and posterior margins; 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 two groups of long setae on posterior margin, anterodistal corner with one spine accompanied by setae and posterodistal corner with two spines accompanied by setae; 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. 29C, D): coxal plate concave, bearing two fine setae on anterior margin and five setae on posterior margin; basis with setae along anterior and posterior margins; merus with four clusters of setae on posterior margin and one spine accompanied by one seta on anterior margin, anterodistal corner with one spine accompanied by setae; carpus and propodus with three or four 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. 29E, F): coxal plate bearing one seta on anterior and posterior margins, respectively; basis expanded, with two setae and six spines on anterior margin, anterodistal corner with two spines accompanied by setae, posterior margin with a row of 13 setae; merus with two clusters of short setae on anterior margin and one spine accompanied by one seta on posterior margin, anterodistal corner with one spine accompanied by setae and posterodistal corner with two spines accompanied by setae; carpus and propodus with groups of spines accompanied by fine setae on anterior margins; dactylus with one plumose seta on posterior margin, and two setae at hinge of unguis.

Pereopod VI (Fig. 29G, H): coxal plate bearing one seta on posterior margin; basis elongated, with two setae and three spines on anterior margin, anterodistal corner with two spines accompanied by setae, posterior margin with a row of nine setae; merus with two spines accompanied by setae on anterior margin and one spine accompanied by one seta on posterior margin, anterodistal and posterodistal corners with two and three spines accompanied by setae respectively; carpus and propodus with three groups of spines accompanied by setae on anterior margins; dactylus with one plumose seta on posterior margin, and two setae at hinge of unguis.

Pereopod VII (Figs 29I, J): coxal plate with three setae on posterior margin; basis with two setae and four spines on anterior margin, anterodistal corner with two spines accompanied by setae, posterior margin with a row of 12 setae and one spine; merus with two groups of spines accompanied by setae on anterior margin and one spine accompanied by one seta on posterior margin, anterodistal and posterodistal corners with three and two spines accompanied by one seta, respectively; carpus and propodus with two or three groups of spines on anterior margins; dactylus with one plumose seta on posterior margin, and two setae at hinge of unguis.

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

Pleon.Epimeral plates (Fig. 30 A–C): plate I ventrally rounded, bearing eight long setae on anteroventral margin and five setae on posterior margin; plate II with one seta and one spine on ventral margin and seven setae on posterior margin, posterodistal corner subacute; plate III with one seta and two spines on ventral margin and six setae on posterior margin, posterodistal corner subacute.

Pleopods I–III (Fig. 30 D–F): similar, peduncle with two or three retinacula accompanied by one or two setae; outer ramus slightly shorter than inner ramus, both rami fringed with plumose setae.

Urosome.Urosomites (Fig. 28E): urosomite I with one-one-one-one spines accompanied by setae on dorsal margin; urosomite II with one-one-one spines accompanied by setae on dorsal margin; urosomite III with one spine accompanied by two setae on each side.

Uropods I–III (Fig. 30 G–I): uropod I peduncle with no basofacial spine and outer margin with one spine, 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 short, peduncle bearing one distal spine on each corner; inner ramus with two spines on inner margin; outer ramus with one spine and two spines on inner and outer margins, respectively; both rami with five terminal spines. Uropod III peduncle with three setae on surface and six distal spines; inner ramus 2.2 times as long as peduncle, reaching 0.9 times the length of outer ramus, with one spine accompanied by ten plumose setae and three simple setae on inner margin, with six plumose setae on outer margin and one spine accompanied by long setae distally; proximal article of outer ramus with three clusters of spines accompanied by simple setae on outer margin, with eight plumose setae on inner margin, and four distal spines, terminal article vestigial, with simple setae.

Telson (Fig. 29K): deeply cleft, approx. as long as wide, left lobe with two simple setae and two plumose setae on surface and with one distal spine accompanied by three setae; right lobe with one simple seta and two plumose setae on surface and with two distal spines accompanied by two setae.

Description of paratype female

(IZCAS-I-A1566-2). 7.3 mm.

Pereon.Gnathopod I (Fig. 31A, B): coxal plate bearing two setae on anterior margin and three setae on posterior margin; basis with long setae on anterior and posterior margins; propodus oval, palm with ten spines on posterior margin, bearing long setae along anterior and posterior margins; dactylus with one seta on outer margin.

Gnathopod II (Fig. 31C, D): coxal plate bearing three setae on anterior and posterior margins each; 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.

Pereopod III (Fig. 32A): merus and carpus with shorter setae on posterior margins than that of male.

Pereopods IV–VII (Fig. 32 B–E): similar to those of male.

Oostegite (Fig. 32 I–L): oostegite of gnathopod II broad, with marginal setae, oostegites of pereopods III and IV elongated, oostegite of pereopod V smallest.

Urosome.Uropods I–III (Figs 30J; 32F, G): uropod I peduncle with no basofacial spine and outer margin with three spines, 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 margin and one spine on outer margin; both rami with five terminal spines. Uropod II short, peduncle bearing one spine on inner margin, each corner with one distal spine; outer ramus with one spine on outer and inner margins each; inner ramus with two spines on inner margin; both rami with five terminal spines. Uropod III peduncle with three setae on surface and five distal spines accompanied by setae; inner ramus 1.5 times as long as peduncle, reaching 0.9 times the length of proximal article of outer ramus, with one spine and plumose setae on inner margin, two plumose setae and one simple seta on outer margin; proximal article of outer ramus with three pairs of spines accompanied by simple setae on outer margin and five plumose setae on inner margin, terminal article much shorter than adjacent spines.

Telson (Fig. 32H): cleft, 0.9 times as long as wide, each lobe with simple setae on surface and with one distal spine accompanied by setae.

Habitat.

The species was collected in Qinglong Cave Park. The park has a limestone karst mountain landscape. There is an underground river winding through the cave before flowing into a pool. Individuals are found along the bank of river, with no vegetation.

Remarks.

The new species of Gammarus longdong Hou & Li, sp. n. is similar to G. craspedotrichus Hou & Li, 2002 in antenna II with long setae along peduncle margin, calceoli absent; pereopod III merus and carpus with long setae on posterior margins; and uropod I with no basofacial spine. Gammarus longdong Hou & Li, sp. n. can be distinguished from G. craspedotrichus Hou & Li, 2002 by the following characters ( G. craspedotrichus in parentheses): urosomites I and II with four groups of spines and setae (with two clusters of spines and setae); and uropod III terminal article vestigial (short but distinct).

The new species of Gammarus longdong Hou & Li, sp. n. is similar to jidutanxian Hou & Li, sp. n. in antenna II peduncle with long setae, calceoli absent; and uropod III outer ramus with no plumose setae on outer margin. It can be distinguished from G. jidutanxian Hou & Li, sp. n. ( G. jidutanxian in parentheses) in uropod I without basofacial spine (with one basofacial spine); and uropod III inner ramus reaching 0.9 times the length of outer ramus (inner ramus 0.6 times the length of outer ramus).

The new species is similar to G. egregius Hou, Li & Li, 2013 in accessory flagellum of antenna I with four articles; antenna II calceoli absent; and uropod I peduncle without basofacial spine. The new species can be distinguished from G. egregius Hou, Li & Li, 2013 by the following characters ( G. egregius in parentheses): urosomite I with one-one-one-one spines accompanied by setae on dorsal margin (bare); urosomite II with one-one-one spines accompanied by setae on dorsal margin (with two single spines); inner ramus of uropod III 0.9 times the length of proximal article of outer ramus (0.6 times the length of outer ramus); and both rami of uropod III with plumose setae on inner margins (simple setae).

The new species is similar to G. platvoeti Hou & Li, 2003a in accessory flagellum of antenna I with four articles; antenna II calceoli absent; epimeral plates II and III with subacute posterodistal corners; and uropod I peduncle without basofacial spine. It differs from G. platvoeti Hou & Li, 2003a ( G. platvoeti in parentheses) by merus and carpus of pereopod III with long setae on posterior margins (with a few short setae); urosomites I and II with spines accompanied by setae on dorsal margin (only with setae); inner ramus of uropod III 0.9 times the length of proximal article of outer ramus (0.85 times the length of outer ramus); and both lobes of telson with simple and plumose setae on surface (bare).