Gammarus pisinnus, Hou & Li & Li, 2014

Hou, Zhonge, Li, Junbo & Li, Shuqiang, 2014, Diversification of low dispersal crustaceans through mountain uplift: a case study of Gammarus (Amphipoda: Gammaridae) with descriptions of four novel species, Zoological Journal of the Linnean Society 170 (4), pp. 591-633 : 623-631

GAMMARUS PISINNUS SP. NOV. ( FIGS 22–27)

Material examined

Holotype (IZCAS-I-A1254-1), male, 8.6 mm, Huo Spring (36°18′N, 111°48′E), altitude 580 m, Hongdong County, Linfen City , Shanxi Province, China, 31.v.2012, collected by J. Li and Z. Chen. Paratypes (from IZCAS-I-A1254-2 to IZCAS-I-A1254-12), six males and five females, same data as holotype .

Other material

Six males and six females (from IZCAS-I-A1227-1 to IZCAS-I-A1227-12, voucher number 1227), Queen Spring (36°41′N, 112°32′E), altitude 1034 m, Qinxian County, Shanxi Province, China, 7.v.2012, collected by J. Li and Z. Chen. Five males and five females (from IZCAS-I-A1229-1 to IZCAS-I-A1229-10, voucher number 1229), Nianziguan Spring (37°58′N, 113°52′E), altitude 370 m, Yangquan City, Shanxi Province, China, 9.v.2012, collected by J. Li and Z. Chen. Ten males and six females (from IZCAS- I-A1216-1 to IZCAS-I-A1216-16, voucher number 1216), Chitougou Spring (35°28′N, 112°32′E), altitude 581 m, Beiliu Town, Yangcheng County, Shanxi Province, China, 2.v.2012, collected by J. Li and Z. Chen. Seven males and five females (from IZCAS-I-A1221-1 to IZCAS-I-A1221-12, voucher number 1221), Xin’an Spring (36°22′N, 113°23′E), altitude 919 m, Lucheng County, Shanxi Province, China, 5.v.2012, collected by J. Li and Z. Chen.

Etymology

The specific name is from the Latin pisinnus (little), indicating the small size of this species; adjective.

Diagnosis

Eyes reniform; merus to carpus of pereopod 3 with long, straight setae on posterior margin; epimeral plates 2, 3 with few seta on posterior margin; inner ramus of uropod 3 reaching about 0.6 times length of outer ramus.

Description

Holotype: male

Body length: 8.6 mm.

Head ( Fig. 22A): eyes reniform, inferior antennal sinus deep, lateral cephalic lobe nearly straight.

Antenna 1 ( Fig. 22B, C): peduncular articles 1–3 in length ratio 1.0:0.9:0.4, with distal setae; flagellum with 28 articles, most with aesthetascs; accessory flagellum with four articles; both primary and accessory flagella with short distal setae.

Antenna 2 ( Fig. 22D, E): peduncular articles 3–5 in length ratio 1.0:2.8:2.6, peduncular articles 4, 5 with clusters of lateral and medial setae; flagellum with 12 articles; calceoli present in articles 1–7.

Upper lip ( Fig. 22F): ventral margin rounded, bearing minute setae.

Mandible ( Fig. 22H, I): left mandible incisor with five teeth; lacinia mobilis with four teeth, spine row with six pairs of plumose setae along ventral margin; palp articles 1–3 in length ratio 1.0:2.0:1.8; article 2 armed with 12 marginal setae; article 3 with six A-setae and four B-setae, plus 16 D-setae and five E-setae apically; incisor of right mandible with four teeth, lacinia mobilis bifurcate, with small teeth.

Lower lip ( Fig. 22G): inner lobes lacking, outer lobes covered with thin setae.

Maxilla 1 asymmetrical ( Fig. 22J, K), left inner plate with 18 plumose setae on medial margin; outer plate with 11 robust, serrated apical spines, each spines with small teeth; article 2 of palp with nine slender spines and one seta apically; article 2 of right palp with five stout spines, one stiff seta, and one slender spine.

Maxilla 2 ( Fig. 22L): inner plate with 15 plumose setae in an oblique row; inner and outer plates with long setae apically.

Maxilliped ( Fig. 22M): inner plate with three stout apical spines and one subapical spine, some plumose setae along ventral margin; outer plate bearing a row of blade-like spines and four plumose setae apically; palp article 4 hooked, with a group of setae at hinge of unguis.

Gnathopod 1 ( Fig. 23A, C ): coxal plate bearing four setae on anterior margin and one seta on posterior margin; 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 11 spines on posterior margin and facial surface; dactylus with one seta on outer margin.

Gnathopod 2 ( Fig. 23B, D ): coxal plate bearing three setae on anterior margin and one seta on posterior margin; basis with long setae on anterior and posterior margins, posterodistal corner with short setae; carpus about 1.5 times as long as wide, about 0.6 times as long as propodus, bearing six clusters of setae along ventral margin, two clusters of setae on dorsal margin; propodus palm ovate, palm margin with one medial spine and five spines on lateral posterodistal corner; dactylus with one seta on outer margin.

Pereopod 3 ( Fig. 24A, F ): coxal plate bearing two setae on anteroventral margin and one seta on posterior margin; basis elongate, with setae along posterior margins; merus with long, straight setae on posterior margin; carpus to propodus with groups of spines accompanied by long setae on posterior margin; dactylus with one plumose seta on posterior margin, and two setae at hinge of unguis.

Pereopod 4 ( Fig. 24B, G ): coxal plate excavated, bearing two setae on anterior margin and three setae on posterior margin; basis with setae on posterior margin; merus with straight setae on posterior margin; carpus to propodus with groups of spines accompanied by setae on posterior margin; dactylus with one plumose seta on posterior margin and two setae at hinge of unguis.

Pereopod 5 ( Fig. 24C, H ): coxal plate bearing one seta on anterior margin and two setae on posterior margin; basis with four spines on anterior margin, anterodistal corner with one spine, posterior margin with a row of eight setae; merus to propodus with groups of spines on anterior margin; dactylus with one plumose seta on posterior margin and two setae at hinge of unguis.

Pereopod 6 ( Fig. 24D, I ): coxal plate bearing one seta on posterior margin; basis elongate, with three setae and four spines on anterior margin, anterodistal corner with two spines, posterior margin dwindling distally, with a row of eight setae; merus to propodus with groups of spines on anterior margin, propodus with two groups of setae on posterior margin; dactylus with one plumose seta on posterior margin and two setae at hinge of unguis.

Pereopod 7 ( Fig. 24E, J ): coxal plate bearing one seta on anterior margin and three setae on posterior margin; basis with three setae and three spines on anterior margin, anterodistal corner with one spine, posterior margin with a row of eight setae; merus to propodus with groups of spines on anterior margin, propodus with two groups of setae on posterior margin; dactylus with one plumose seta on posterior margin and two setae at hinge of unguis.

Coxal gills: coxal gill of gnathopod 2 and gills of pereopods 3–5 a little shorter than bases; gill of pereopod 6 more than half length of basis; gill of pereopod 7 smallest, less than half of basis.

Epimeral plates ( Fig. 25A–C): plate 1 ventrally rounded, bearing three setae on anteroventral margin, two setae on posterior margin; plate 2 with two spines on ventral margin, one seta on posterior margin, posterodistal corner subacute; plate 3 with three spines on ventral margin, one seta on posterior margin, posterodistal corner acute.

Pleopods 1–3 similar ( Fig. 25E–G), peduncles with two retinacula accompanied by one or two setae; outer ramus slightly shorter than inner ramus, both rami fringed with plumose setae.

Urosomites 1–3 ( Fig. 25D): urosomite 1 with twotwo−two spines accompanied by setae on dorsal margin. Urosomite 2 with two−two−two spines accompanied by setae on dorsal margin. Urosomite 3 with two spines accompanied by setae on each side and one cluster of setae on dorsal margin.

Uropods 1–3 ( Fig. 25H–J): uropod 1 peduncle with one basofacial spine, two spines on outer margin, one spine on inner margin, two and one spines on outer and inner distal corners, respectively; outer ramus with one spine on inner margin; inner ramus with two spines on inner margin; both rami with five terminal spines. Uropod 2 short, peduncle bearing one spine on outer margin and one spine on inner margin, with one distal spine on each corner; outer ramus with one spine on each margin; inner ramus with two spines on inner margin. Uropod 3 peduncle with one spine accompanied by two setae on surface and four distal spines; inner ramus about 1.6 times as long as peduncle, reaching 0.6 times the length of outer ramus, with two spines on inner margin accompanied by plumose setae, bearing two apical spines accompanied by simple setae; article 1 of outer ramus with three pairs of spines on outer margin, both margins set with plumose setae; terminal article longer than adjacent spines.

Telson ( Fig. 25K): deeply cleft, as long as wide, each lobe with setae and one spine accompanied by two setae on surface, bearing three distal spines accompanied by setae.

Female, paratype (IZCAS-I-A1254-2)

Body length: 6.8 mm.

Gnathopod 1 ( Fig. 26A, C): coxal plate bearing two setae and one seta on anterior and posterior margins, respectively; basis with long setae on anterior and posterior margins; propodus oval, palm with five spines on posterior margin; dactylus with one seta on outer margin.

Gnathopod 2 ( Fig. 26B, D): coxal plate bearing three setae and one seta on anterior and posterior margins, respectively; basis with setae on anterior and posterior margins, posterodistal corner with short setae; propodus subrectangular, palm margin with four spines on posterodistal corner, bearing simple setae along anterior and posterior margins; dactylus with one seta on outer margin.

Pereopods 3, 4 ( Fig. 27A, B ): with shorter setae on posterior margin than those of male.

Pereopods 5–7 ( Fig. 27C–E ): similar to those of male, but a little stout.

Uropods 1–3 ( Fig. 25L–N): uropods 1 and 2 similar to those of male. Uropod 3 peduncle with one spine accompanied by one seta on surface and three distal spines; inner ramus about 1.1 times as long as peduncle, reaching 0.5 times the length of outer ramus, with one spine and plumose setae on lateral margin; article 1 of outer ramus with three pairs of spines accompanied by simple setae and plumose setae on outer margin; terminal article longer than adjacent spines.

Telson ( Fig. 27F ): cleft, each lobe with one or two setae and one spine accompanied by one seta on surface, bearing four distal spines accompanied by two setae.

Oostegite ( Fig. 27G–J ): oostegite of gnathopod 2 broad, with marginal setae, oostegites of pereopods 3 and 4 elongate, oostegite of pereopod 5 smallest.

Habitat

Gammarus pisinnus sp. nov. has been found in southern parts of the Taihang Mts. All known individuals have been collected from springs. Many springs in this area have disappeared or diminished because of groundwater exploitation. As a consequence, some endemic species have suffered population losses or become extinct, and efforts should be made to conserve this vulnerable habitat.

Remarks

Gammarus pisinnus sp. nov. is similar to its sibling species G. clarus in epimeral plate 3 with acute posterior corner and both margins of uropod 3 with plumose setae. This new species differs from G. clarus (character states in parentheses) in urosomites 1 and 2 flat (elevated); basis of pereopods 6 and 7 broad (proximally broad, distally narrow); telson with long setae on the surface (with a few short setae).

Gammarus pisinnus sp. nov. resembles G. nekkensis , which was redescribed by Karaman (1989), in the shape of epimeral plates and the ratio between inner and outer ramus of uropod 3. Gammarus

Figures

Figure 23. Gammarus pisinnus sp. nov., holotype, male. A, gnathopod 1; B, gnathopod 2; C, propodus of gnathopod 1; D, propodus of gnathopod 2.

Figure 24. Gammarus pisinnus sp. nov., holotype, male. A, pereopod 3; B, pereopod 4; C, pereopod 5; D, pereopod 6; E, pereopod 7; F, dactylus of pereopod 3; G, dactylus of pereopod 4; H, dactylus of pereopod 5; I, dactylus of pereopod 6; J, dactylus of pereopod 7.

Figure 27. Gammarus pisinnus sp. nov., female. A, pereopod 3; B, pereopod 4; C, pereopod 5; D, pereopod 6; E, pereopod 7; F, telson; G, oostegite of gnathopod 2; H, oostegite of pereopod 3; I, oostegite of pereopod 4; J, oostegite of pereopod 5.