Gammarus incoercitus, 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 : 599-607

GAMMARUS INCOERCITUS SP. NOV. ( FIGS 4–9)

Material examined

Holotype (IZCAS-I-A1236-1), male, 11.3 mm, a spring in Fanjia Village (39°24′N, 111°23′E), altitude 1008 m, Pianguan County, Xinzhou City, Shanxi Province, China, 20.v.2012, collected by J. Li and Z. Chen. Paratypes (from IZCAS-I-A1236-2 to IZCAS-I- A1236-15): eight males and six females, same data as holotype .

Other material

Three males and two females (from IZCAS-I-A1237-1 to IZCAS-I-A1237-5, voucher number 1237), altitude 1017 m, a brook through Fanjia Village (39°26′N, 111°24′E), Pianguan County, Xinzhou City, Shanxi Province, China. 20.v.2012, collected by J. Li and Z. Chen. Eight males and five females (from IZCAS-I- A1243-1 to IZCAS-I-A1243-13, voucher number 1243), Sanchuan River (37°26′N, 110°55′E), altitude 805 m, Liulin County, Shanxi Province, China, 25.v.2012, collected by J. Li and Z. Chen. Three males and three females (from IZCAS-I-A1128a-1 to IZCAS-I- A1128a-6, voucher number 1128a), Huaidao Town (38°40′N, 112°14′E), altitude 1679 m, Ningwu County, Shanxi Province, China, 1.ix.2010, collected by Y. Zong. Twelve males and ten females (from IZCAS-I-A1238-1 to IZCAS-I-A1238-22, voucher number 1238), Leiming Temple (38°49′N, 112°05′E) near the source of the Fenhe River, altitude 1601 m, Ningwu, Shanxi Province, China, 23.v.2012, collected by J. Li and Z. Chen. Nine males and two females (from IZCAS-I-A1240-1 to IZCAS-I-A1240-11, voucher number 1240), source of the Fenhe River (38°48′N, 112°05′E), altitude 575 m, Ningwu County, Shanxi Province, China, 23.v.2012, collected by J. Li and Z. Chen.

Etymology

The specific name is from the Latin incoercitus (free), referring to freely swimming for this animal.

Diagnosis

Merus to carpus of pereopod 3 with long, curled setae on posterior margin; epimeral plates 2, 3 with suba- cute posterodistal corners; inner ramus of uropod 3 reaching about 0.6 times the length of outer ramus, outer margin with two groups of spines but few setae.

Description

Holotype, male

Body length: 11.3 mm.

Head ( Fig. 4A): eyes reniform, inferior antennal sinus deep, lateral cephalic lobe nearly straight.

Antenna 1 ( Fig. 4B, C): peduncular articles 1–3 in length ratio 1.0:0.7:0.4, with setae on distal corners; flagellum with 26 articles bearing aesthetascs; accessory flagellum with four articles; both primary and accessory flagella with short distal setae.

Antenna 2 ( Fig. 4D, E): peduncular articles 3–5 in length ratio 1.0:3.6:3.8, peduncular articles 4, 5 with clusters of lateral and medial setae; flagellum with ten articles and one tiny distal article, calceoli present in articles 1–7.

Upper lip ( Fig. 4F): ventral margin rounded, bearing minute setae.

Mandible ( Fig. 4H, I): left mandible incisor with five teeth; lacinia mobilis with four teeth, spine row with seven pairs of plumose setae along ventral margin; palp articles 1–3 in length ratio 1.0:2.9:1.8; article 2 armed with 11 marginal setae; article 3 with three A-setae and two clusters of B-setae, plus 21 D-setae and five E-setae apically; incisor of right mandible with four teeth, lacinia mobilis bifurcate, with small teeth.

Lower lip ( Fig. 4G): inner lobes lacking, outer lobes covered with thin setae.

Maxilla 1 asymmetrical ( Fig. 4J, K), left inner plate with 14 plumose setae on medial margin; outer plate with 11 robust serrated apical spines, each spines with small teeth; article 2 of palp with seven slender spines and two stiff setae apically; article 2 of right palp with six stout spines and one stiff seta and one slender spine.

Maxilla 2 ( Fig. 4L): inner plate with 15 plumose facial setae in an oblique row; inner and outer plates with long setae apically.

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

Gnathopod 1 ( Fig. 5A, C): coxal plate bearing two setae and one seta on anterior and posterior margins, respectively; basis with setae on anterior and posterior margins; carpus about 1.6 times as long as wide, about 0.7 times as long as propodus, posterior margin bearing short setae; propodus oval, palm with one medial spine and 14 spines on posterior margin and facial surface; dactylus with one seta on outer margin.

Gnathopod 2 ( Fig. 5B, D): coxal plate bearing two setae and one seta on anterior and posterior margins, respectively; basis with setae on anterior and posterior margins, posterodistal corner with short setae; carpus about 1.6 times as long as wide, about 0.8 times as long as propodus, bearing eight clusters of setae along ventral margin, two clusters of setae on dorsal margin; propodus palm margin with one medial spine and five spines on lateral posterodistal corner; dactylus with one seta on outer margin.

Pereopod 3 ( Fig. 6A, F ): coxal plate bearing two setae and one seta on anteroventral and posterior margins; basis elongate, with setae along anterior and posterior margins; merus with long, curled setae on posterior margin; carpus with groups of spines accompanied by long, curled setae on posterior margin; propodus with six groups of spines accompanied by short setae on posterior margin; dactylus with one plumose seta on posterior margin, and two setae at hinge of unguis.

Pereopod 4 ( Fig. 6B, G ): coxal plate excavated, bearing two setae on anterior margin and six setae on posterior margin; merus with clusters of 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. 6C, H ): coxal plate bearing one seta on anterior and posterior margins, respectively; basis with five spines on anterior margin, anterodistal corner with two spines, posterior margin with a row of ten 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. 6D, I ): coxal plate bearing one seta on posterior margin; basis elongate, with two setae and five spines on anterior margin, anterodistal corner with two spines, posterior margin dwindling distally, with a row of 12 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 7 ( Fig. 6E, J ): coxal plate bearing four setae on posterior margin; basis with four setae and five spines on anterior margin, anterodistal corner with two spines, posterior margin with a row of 15 setae; merus to propodus with groups of spines accompanied by a few setae on anterior 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. 7A–C ): plate 1 ventrally rounded, bearing three setae on anteroventral margin and three setae on posterior margin; plate 2 with three spines on ventral margin, three setae on posterior margin, posterodistal corner subacute; plate 3 with four spines on ventral margin, three setae on posterior margin, posterodistal corner acute.

Pleopods 1–3 similar ( Fig. 7E–G ), peduncles with one or 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. 7D ): urosomite 1 with two−two−two spines accompanied by setae on dorsal margin. Urosomite 2 with three−two−two spines accompanied by setae on dorsal margin. Urosomite 3 with one spine and three spines accompanied by one seta on each side.

Uropods 1–3 ( Fig. 7H–J ): uropod 1 peduncle with one basofacial spine, with two spines on outer and inner margins, two and one spine on outer and inner distal corners, respectively; both rami with two spines on inner margins and five terminal spines. Uropod 2 short, peduncle bearing one spine on each margin and one distal spine on each corner; inner and outer rami both with one spine on inner margins and five terminal spines. Uropod 3 peduncle with one spine on surface and five 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, with plumose setae and a few simple setae along inner and outer margins, bearing two apical spines accompanied by simple setae; article 1 of outer ramus with three pairs of spines accompanied by simple setae and a few plumose setae on outer margin; terminal article with simple setae, longer than adjacent spines.

Telson ( Fig. 7K ): completely cleft, as long as wide, each lobe with three clusters of setae and one spine accompanied by setae on surface, with two distal spines accompanied by setae.

Female, paratype (IZCAS-I-A1236-2)

Body length: 9.8 mm.

Gnathopod 1 ( Fig. 8A, C ): coxal plate bearing two setae on anterior margin and one seta on posterior margin; basis with setae on posterior margin; propodus oval, palm with six spines on posterior margin; dactylus with one seta on outer margin.

Gnathopod 2 ( Fig. 8B, D ): coxal plate bearing two setae on anterior margin and one seta on posterior margin; basis with short setae on anterior and posterior margins, posterodistal corner with short setae; propodus subrectangular, palm margin with six spines on posterodistal corner, bearing simple setae along anterior and posterior margins; dactylus with one seta on outer margin.

Pereopods 3, 4 ( Fig. 9A, B ): with shorter setae on posterior margin than those of male.

Pereopods 5–7 ( Fig. 9C–E ): similar to those of male.

Uropods 1–3 ( Fig. 7L–N ): uropods 1 and 2 similar to those of male. Uropod 3 peduncle with one spine accompanied by two setae on surface and six distal spines; inner ramus about 1.3 times as long as peduncle, reaching 0.6 times the length of outer ramus, with one spine and some plumose setae on lateral margin; article 1 of outer ramus with two pairs of spines and one single spine accompanied by simple setae and three plumose setae on outer margin; terminal article longer than adjacent spines.

Telson ( Fig. 9F ): cleft, similar to that of male.

Oostegite ( Fig. 9G–J ): oostegite of gnathopod 2 broad, with marginal setae, oostegites of pereopods 3 and 4 elongate, oostegite of pereopod 5 smallest.

Habitat

Gammarus incoercitus sp. nov. was found in six localities in northern parts of the Lüliang Mts. Specimens were collected near the source of the Fenhe River or upper reaches of brooks with no signs of pollution.

Remarks

The genus Gammarus is widely distributed throughout the Northern Hemisphere. Up to now, there are about 70 recorded species in China, which are separated into north-west and south-east groups driven by the uplift of the Tibet Plateau ( Hou et al., 2007). The species discussed in this paper belong to the southeast group.

This new species, G. incoercitus , can be distinguished from the closely related species G. shanxiensis (character states in parentheses) by the following characters: merus to carpus of pereopod 3 with long, curled setae on posterior margin (with short setae on posterior margin); epimeral plate 3 with acute posterodistal corner (subacute); and inner ramus of uropod 3 reaching about 0.6 times the length of outer ramus (0.8 times the length of outer ramus).

Gammarus incoercitus differs from Gammarus martensi Hou & Li, 2004 (states in parentheses) by antenna 2 with short setae (densely with long setae); epimeral plates 2 and 3 acute (blunt); and urosomites 1–3 with dorsal spines accompanied by short setae (with long dorsal setae).

Figures

Figure 6. Gammarus incoercitus 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 7. Gammarus incoercitus sp. nov., male, A–K; female, L–N. A, epimeral plate 1; B, epimeral plate 2; C, epimeral plate 3; D, urosomites (dorsal view); E, pleopod 1; F, pleopod 2; G, pleopod 3; H, uropod 1; I, uropod 2; J, uropod 3; K, telson; L, uropod 1; M, uropod 2; N, uropod 3.

Figure 8. Gammarus incoercitus sp. nov., female. A, gnathopod 1; B, gnathopod 2; C, propodus of gnathopod 1; D, propodus of gnathopod 2.

Figure 9. Gammarus incoercitus 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.