Gammarus benignus, 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 : 607-615

GAMMARUS BENIGNUS SP. NOV. ( FIGS 10–15)

Material examined

Holotype (IZCAS-I-A1207-1), male, 11.2 mm, Wulaofeng Natural Landscape Area (34°48′N, 110°34′E), altitude 1018 m, Yongji County, Shanxi Province, China, 29.iv.2012, collected by J. Li and Z. Hou.

Paratypes (from IZCAS-I-A1207-2 to IZCAS-I-A1207- 25): 15 males and nine females, same data as holotype .

Other material

Five males and five females (from IZCAS-I-A1241-1 to IZCAS-I-A1241-10, voucher number 1241), Pangquangou Natural Reserve (37°53′N, 111°26′E), altitude 1936 m, Fangshan County, Shanxi Province, China, 24.v.2012, collected by J. Li and Z. Chen.

Etymology

The specific name is from the Latin benignus (kind), in reference to the nice habitat of this species; adjective.

Diagnosis

Eyes oval; pereopod 3 with long, straight setae on posterior margin; epimeral plates 2, 3 with blunt posterodistal corners; uropod 3 slender, inner ramus reaching about 0.4 times the length of outer ramus.

Description

Holotype: male

Body length: 11.2 mm.

Head ( Fig. 10A): eyes oval, inferior antennal sinus deep, lateral cephalic lobe nearly straight.

Antenna 1 ( Fig. 10B, C): peduncular articles 1–3 in length ratio 1.0:0.8:0.4, with distal setae; flagellum with 35 articles, most with aesthetascs; accessory flagellum with five articles; both primary and accessory flagella with short distal setae.

Antenna 2 ( Fig. 10D, E): peduncular articles 3–5 in length ratio 1.0:3.8:3.6, peduncular articles 4, 5 with clusters of lateral and medial setae; flagellum with 15 articles and one tiny distal article, bearing setae along ventral margins; calceoli present in articles 1–8.

Upper lip ( Fig. 10F): ventral margin rounded, bearing minute setae.

Mandible ( Fig. 10H, I): left mandible incisor with five teeth; lacinia mobilis with four teeth, spine row with five pairs of plumose setae along ventral margin; palp articles 1–3 in length ratio 1.0:2.5:1.7; article 2 armed with 15 marginal setae; article 3 with four A-setae and two clusters of 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. 10G): inner lobes lacking, outer lobes covered with thin setae.

Maxilla 1 asymmetrical ( Fig. 10J, K), left inner plate with 13 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 two stiff setae apically; article 2 of right palp with five stout spines, one stiff seta and one slender spine.

Maxilla 2 ( Fig. 10L): inner plate with 14 plumose facial setae in an oblique row; inner and outer plates with long setae apically.

Maxilliped ( Fig. 10M): 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 three plumose setae apically; palp article 4 hooked, with a group of setae at hinge of unguis.

Gnathopod 1 ( Fig. 11A, C ): coxal plate bearing three and five setae on anterior and posterior margins, respectively; basis with setae on anterior and posterior margins; carpus about 1.3 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 18 spines on posterior margin and facial surface, respectively; dactylus with one seta on outer margin.

Gnathopod 2 ( Fig. 11B, D ): coxal plate bearing four setae on anterior margin and four setae on posterior margin; basis with setae on anterior and posterior margins, posterodistal corner with short setae; carpus about 1.7 times as long as wide, about 0.8 times as long as propodus, with parallel margins, bearing eight 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 posterodistal corner; dactylus with one seta on outer margin.

Pereopod 3 ( Fig. 12A, F ): coxal plate bearing four setae and three setae on anteroventral and posterior margins, respectively; basis elongate, with short setae along anterior and posterior margins; merus to carpus with long, straight setae on posterior margin; carpus with groups of spines on posterior margin; propodus with five 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. 12B, G ): coxal plate excavated, bearing three setae on anterior margin and seven setae on posterior margin; basis with one spine accompanied by short setae on anterodistal corner; merus with clusters of setae on posterior margin and one spine on anterior margin, anterodistal corner with one spine accompanied by some setae; carpus and propodus with groups of spines accompanied by short setae on posterior margin; dactylus with one plumose seta on anterior margin and two setae at hinge of unguis.

Pereopod 5 ( Fig. 12C, H ): coxal plate bearing four setae on posterior margin; basis with two clusters of setae and six spines on anterior margin, anterodistal corner with two spines, posterior margin 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 6 ( Fig. 12D, I ): coxal plate bearing one seta and three setae on anterior and posterior margins, respectively; basis elongate, with two clusters of setae and five spines on anterior margin, anterodistal corner with two spines, posterior margin dwindling distally, with a row of 17 setae; merus to propodus with groups of spines on anterior margin, propodus with three groups of setae on posterior margin; dactylus with one plumose seta on posterior margin, and two setae at hinge of unguis.

Pereopod 7 ( Fig. 12E, J ): coxal plate bearing five setae on posterior margin; basis with two clusters of setae and four spines on anterior margin, anterodistal corner with two spines, posterior margin with a row of 18 setae, inner surface with one spine accompanied by one seta; merus to propodus with groups of spines accompanied by few setae on anterior margin, propodus with two clusters 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 5 more than half length of basis; gill of pereopod 7 smallest, less than half of basis.

Epimeral plates ( Fig. 13A–C ): plate 1 ventrally rounded, bearing four long setae and four short setae on anteroventral margin, with four setae on posterior margin; plate 2 with two spines on ventral margin and three setae on posterior margin, posterodistal corner blunt; plate 3 with four spines on ventral margin and six setae on posterior margin, posterodistal corner blunt.

Pleopods 1–3 similar ( Fig. 13E–G ), peduncles with one or two retinacula accompanied by one setae; inner and outer rami fringed with plumose setae.

Urosomites 1–3 ( Fig. 13D ): urosomite 1 with onetwo−one spine accompanied by setae on dorsal margin. Urosomite 2 with two−one−one−two spines accompanied by setae on dorsal margin. Urosomite 3 with two spines accompanied by one seta on each side.

Uropods 1–3 ( Fig. 13H–J ): uropod 1 peduncle with one basofacial spine, three spines on outer margin and one spine on inner margin, with two and one spines on outer and inner distal corners, respectively; outer ramus with two spines on outer margin and one spine on inner margin; inner ramus with one spine on inner margin; both rami with five terminal spines. Uropod 2 short, peduncle bearing two spines on outer margin, with one distal spine on each corner; outer ramus with one spine on outer margin and one spine on inner margin; inner ramus with two spines on inner margin. Uropod 3 slender, peduncle with one spine accompanied by two setae on surface and five distal spines; inner ramus about 1.2 times as long as peduncle, reaching 0.4 times the length of outer ramus, with one spine accompanied by plumose setae on inner margin, bearing three apical spines accompanied by simple setae; article 1 of outer ramus with two pairs of spines and one single spine on outer margin, both margins with plumose setae; terminal article slightly shorter than adjacent spines.

Telson ( Fig. 13K ): deeply cleft, as long as wide, each lobe with one spine accompanied by three setae and clusters of setae on surface, bearing two distal spines accompanied by five setae.

Female: paratype (IZCAS-I-A1207-2)

Body length: 10.5 mm.

Gnathopod 1 ( Fig. 14A, C ): coxal plate bearing four setae on anterior margin and four setae on posterior margin; basis with setae on anterior and posterior margins; propodus oval, palm with seven spines on posterior margin; dactylus with one seta on outer margin.

Gnathopod 2 ( Fig. 14B, D ): coxal plate bearing five setae and four setae 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. 15A, B ): with shorter setae on posterior margin than those of male.

Pereopods 5–7 ( Fig. 15C–E ): similar to those of male.

Uropods 1–3 ( Fig. 13L–N ): uropods 1 and 2 similar to those of male. Uropod 3 peduncle with one spine accompanied by setae on surface and four distal spines; inner ramus as long as peduncle, reaching 0.4 times the length of outer ramus, with one spine and plumose setae on inner margin; article 1 of outer ramus with two pairs of spines and one single spine accompanied by simple and plumose setae on outer margin, inner margin with one spine and plumose setae; terminal article longer than adjacent spines.

Telson ( Fig. 15F ): cleft, similar to that of male.

Oostegite ( Fig. 15G–J ): oostegite of gnathopod 2 broad, with marginal setae, oostegites of pereopods 3 and 4 elongate, oostegite of pereopod 5 smallest.

Habitat

This species was found in two sites in southern parts of the Lüliang Mts. Samples were collected along brooks flowing from the peak of the mountain, under rotten leaves. However, they are absent near the entrance of the scenic area, probably because of the vast numbers of tourists.

Remarks

Gammarus benignus sp. nov. can be distinguished from its sibling species G. shanxiensis (character states in parentheses) by the following characters: pereopod 3 with long, straight setae on posterior margin (with short setae on posterior margin); epimeral plates 2, 3 posterodistal corners blunt (subacute); and uropod 3 slender, inner ramus reaching about 0.4 times the length of outer ramus (0.8 times the length of outer ramus).

Gammarus benignus sp. nov. differs from G. incoercitus (character states in parentheses) by eyes oval (reniform); pereopod 3 with long, straight setae on posterior margin (curled setae); and inner ramus reaching about 0.4 times the length of outer ramus (0.6 times the length of outer ramus).

Figures

Figure 11. Gammarus benignus sp. nov., holotype, male. A, gnathopod 1; B, gnathopod 2; C, propodus of gnathopod 1; D, propodus of gnathopod 2.

Figure 12. Gammarus benignus 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 13. Gammarus benignus 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 14. Gammarus benignus sp. nov., female. A, gnathopod 1; B, gnathopod 2; C, propodus of gnathopod 1; D, propodus of gnathopod 2.

Figure 15. Gammarus benignus 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.