Gammarus shenmuensis, Hou & Li, 2004

Hou, Z. & Li, S., 2004, Three new species of Gammarus from Shaanxi, China (Crustacea: Amphipoda: Gammaridae), Journal of Natural History 38, pp. 2733-2757 : 2734-2741

Gammarus shenmuensis n. sp.

(figures 1–5)

Material examined. One male (HOLOTYPE), a spring from Doumaogou , Shenmu County (38.8 ‡ N, 110.4 ‡ E), Shaanxi Province, 29 May 1995 . One male and five females (PARATYPES), the same collection data. Four males and one female, a spring from Baiyushan Mt , Jingbian County (37.5 ‡ N, 108.8 ‡ E), Shaanxi Province, 25 May 1995 .

Etymology. This new species is named after its type locality, Shenmu County.

Diagnosis. Antennae 1 and 2 stout, poorly setose (figure 2A, B). Gnathopods 1 and 2 of male without medial spine on propodus palm margin (figure 2C–F), propodus palm of gnathopod 1 not oblique (figure 2D, F). Pereopods 5–7 stout (figure 4A–C). Outer ramus of uropod 2 marginally bare (figure 5F). Article 2 of outer ramus in uropod 3 reaching one-third of article 1 (figure 3D, H).

Description. Male (holotype, IZCAS-I-A0045) 6.3 mm. Eyes medium and oval (figure 1C). Inferior antennal sinus deep (figure 1C). Antenna 1 (figure 2A): peduncular articles 1–3 length ratio 1:0.55:0.36, article 1 stout; primary flagellum with 13 articles, most articles with aesthetascs; accessory flagellum with two articles. Antenna 2 (figure 2B): peduncular article 4 about as long as article 5, both bearing two to three groups of setae on ventral margin; flagellum with eight articles, each article setose, calceoli absent.

Upper lip convex, with minute setae (figure 1F). Left mandible (figure 1A): incisor with five teeth; lacinia mobilis with four weak dentitions; molar triturative; article 2 of palp about 1.12 times as long as article 3, bearing five short and four long setae; article 3 with three A-setae, two B-setae, a row of D-setae and three E-setae (according to Cole, 1980). Right mandible (figure 1L): incisor with four teeth; lacinia mobilis bifurcate, with many teeth; molar with one long seta. Lower lip (figure 1E): inner lobe absent. Maxilla 1 (figure 1H, I, K): inner plate bearing 11 plumose setae; outer plate with 11 serrated spines; article 2 of left palp bearing five sharp spines and one seta; article 2 of right palp bearing five blunt spines and one seta. Maxilla 2 (figure 1G): inner plate with nine plumose setae on inner surface. Maxilliped (figure 1J): inner plate with three stout spines and one subdistal spine.

Coxal plates 1–3 subrectangular (figures 2C, D, 3B), bearing three setae and one seta on anterior and posterior corners, respectively. Coxal plate 4 excavated (figure 3A), with one seta on anterior corner and four setae on posterior margin, respectively. Coxal plates 5–7 shallow (figure 4A–C), bearing two setae on posterior margin. Coxal gills 2–7 sac-like.

Gnathopod 1 (figure 2D, F): palm of propodus not steeply oblique, bearing four spines on posterior corner. Gnathopod 2 (figure 2C, E): carpus and propodus elongate, palm of propodus truncate, bearing four spines on inner margin. Both gnathopods without medial palmar spine on propodus.

Pereopods 3–4 poorly setose (figure 3A, B), with straight setae on posterior margin, carpus shorter than merus and propodus. Pereopods 5–7 stout (figure 4A– C, E–G), progressively longer. Anterior margin of bases weakly convex, bearing one or two long setae and three to five spines; posterior margin nearly straight in pereopods 5 and 6, processed in pereopod 7, with about 10 short setae on posterior margin. Merus to propodus mainly with two to three groups of spines on anterior margins. Dactylus bearing one plumose seta on outer margin and one or two setae at hinge of nail.

Epimeral plates 1–3 progressively acuminate posteriorly (figure 1B), bearing setules on posterior margin. Epimeral plate 1 with six setae on ventral margin; epimeral plate 2 with two short spines on ventral margin; epimeral plate 3 bearing one spine on ventral margin. Pleopods 1–3 subequal (figure 3E–G), peduncle with some setae, bearing two retinaculae accompanied by one or two setae; both rami fringed with plumose setae.

Urosomites 1–3 with long spines dorsally (figures 1D, 2G). Uropod 1 (figure 3C): peduncle bearing one basofacial spine, with marginal spines; outer ramus with one spine on each side; inner ramus with one spine on inner margin. Uropod 2 (figure 5F): peduncle with marginal spines; outer ramus marginally bare; inner ramus with one marginal spine. Uropod 3 (figure 3D): inner ramus 0.62 times as long as article 1 of outer ramus, bearing two distal spines; article 1 of outer ramus with groups of spines on outer margin, article 2 about 0.35 times as long as article 1; both rami with some plumose setae.

Telson cleft (figure 4D), each lobe with two distal spines and one short basofacial spine accompanied by some setae.

Dimorphism. Female, 6.1 mm. Gnathopod 1 (figure 5A, C, D) similar to gnathopod 2, carpus and propodus in length ratio 1:1.13, palm of propodus oblique, bearing seven sharp spines on posterior corner. Gnathopod 2 (figure 5B, E): carpus about as long as propodus, parallel-sided; palm of propodus transverse, bearing one sharp spine on posterior corner.

Pereopods 3–4 bearing some straight setae on posterior margins, carpus shorter than adjacent articles of merus and propodus, especially in pereopod 4. Uropod 3 (figure 3H): peduncle with one dorsal spine and some setae; inner ramus 0.66 times as long as article 1 of outer ramus, bearing one lateral spine and one distal spine; article 1 of outer ramus with two marginal spines and two pairs of distal spines, article 2 elongate, reaching one-third of article 1; both margins of inner ramus and inner margin of outer ramus with some plumose setae.

Oostegites present on pereopods 2–5.

Habitat. Individuals of this species were found in mountain springs.

Remarks. Gammarus shenmuensis n. sp. is similar to species of the genus Stenogammarus Martynov, 1924 , in subequal gnathopods 1 and 2, propodus palm without medial spine; outer ramus of uropod 2 with few spines; article 2 of outer ramus of uropod 3 elongate, attaining one-third of article 1. Gammarus shenmuensis differs from Stenogammarus species in peduncular article 2 of antenna 1 being about half the length of article 1 (peduncular article 2 of antenna 1 being less than one-third of article 1 in Stenogammarus species ); urosomites with dorsal spines and setae (scarcely setulate or weakly spinose in Stenogammarus species ).

Gammarus shenmuensis differs from other Gammarus species by subequal gnathopods 1 and 2, propodus without medial palmar spine; article 2 of uropod 3 elongate.