Gammarus murarius, 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 : 2741-2749

Gammarus murarius n. sp.

(figures 6–11)

Material examined. One male (HOLOTYPE), Zhidan County (36.8 ‡ N, 108.8 ‡ E), Shaanxi Province, 24 May 1995. PARATYPES: four males and four females, Yanchang County (36.5 ‡ N, 110.0 ‡ E), Shaanxi Province, water temperature 7 ‡ C, 23 May 1995 ; seven females and seven males, Zhoujiayuan Villiage , Yanchang County, Shaanxi Province, 23 May 1995 ; 10 males and nine females, Zhidan County, Shaanxi Province, 26 May 1995 .

Etymology. This specific name murarius alludes to the habitat, living in a sump coming from mural water.

Diagnosis. Antennae poorly setose (figure 7B, C). Posterior margin of pereopod 3 with long curled setae (figure 8A). Outer margin of outer ramus of uropod 3 with few plumose setae (figure 9G).

Description. Male (holotype, IZCAS-I-A0047) 8.6 mm. Body white. Eyes black, reniform, medium in size (figure 6A). Antenna 1 (figure 7B): peduncular articles 1–3 length ratio 1:0.68:0.38, primary flagellum with 23 articles, accessory flagellum with four articles. Antenna 2 (figure 7C, H): peduncular article 4 about as long as article 5, both with few setae, flagellum with 10 articles, proximal six articles with calceoli.

Upper lip convex, with apical setae (figure 6D). Mandible (figure 6H, K): incisor with five teeth; lacinia mobilis with weak dentition; spine row with five serrated setae; molar developed; palp article 2 with 11 long marginal setae, palp article 3 with two groups of A-setae, four B-setae, a row of D-setae and five E-setae. Lower lip with fine apical setae (figure 6E). Maxilla 1 asymmetric (figure 6F, G), inner plate with 17 plumose setae on inner margin; outer plate with 11 apical serrated spines; article 2 of left palp with seven apical spines and two setae; article 2 of right palp with six blunt spines and one seta. Maxilla 2 (figure 6J): inner plate with a diagonal row of 14 plumose setae; outer plate with long apical setae. Maxilliped (figure 6I): inner plate with one subdistal and three distal spines; outer plate with 10 slender spines on medial margin and five pectinate setae on distal margin; palp article 3 with distal setae, article 4 unguiform.

Coxal plates 1–3 subrectangular (figures 7D, E, 8A), with three setae on anterior corner and one seta on posterior corner; coxal plate 4 excavated (figure 8B), with two setae on anterior corner and four setae on the posterior margin; coxal plates 5–7 narrow (figure 8C–E), with three to five lateral setae. Coxal gills 2–7 sac-like.

Gnathopod 1 (figure 7D, F): basis stout; carpus pyriform; propodus elongate, palm of propodus oblique, with one medial palmar spine, and 13 spines on inner posterior margin; dactylus with one seta on outer margin and two short setae at joint of nail. Gnathopod 2 (figure 7E, G) larger than gnathopod 1, palm of propodus transverse, with one medial spine and five spines on posterior corner.

Pereopod 3 (figure 8A, F): basis slender, merus and carpus densely setose, with long curled setae on posterior margins; propodus with four spines sequentially. Pereopod 4 (figure 8B, G) with long straight setae on posterior margin.

Pereopod 5 shorter than pereopods 6 and 7 (figure 8C–E, H–J), basis of pereopod 5 subrectangular, bases of pereopods 6 and 7 elongate, inner surface of basis of pereopod 7 with one spine; merus to propodus with groups of spines accompanied by few short setae.

Epimeral plate 1 ventrally rounded, with four setae on anterior corner; epimeral plate 2 blunt on posterodistal corner, with two spines on ventral margin; epimeral plate 3 posterodistally sharp, with two spines on ventral margin (figure 6B). Pleopods 1–3 similar (figure 9B–D), peduncles bearing two retinaculae accompanied by two or three setae; rami fringed with plumose setae.

Urosomites 1–3 with four bundles of spines or setae (figures 6C, 7A). Uropod 1 (figure 9E): peduncle longer than rami, with one basofacial spine, four spines on outer margin and three spines on inner margin; inner ramus with two marginal spines, outer ramus with one marginal spine. Uropod 2 (figure 9F): peduncle as long as outer ramus; inner ramus with one marginal spine; outer ramus with two marginal spines. Uropod 3 (figure 9G): peduncle shorter than inner ramus, with five distal spines and some setae; inner ramus about 0.65 times as long as article 1 of outer ramus; article 1 of outer ramus with six marginal and two distal spines, article 2 small, with lateral and apical setae; both margins of inner ramus and inner margin of outer ramus armed with plumose setae.

Telson deeply cleft (figure 9A), each lobe with two distal spines and one basolateral spine, accompanied by some setae.

Dimorphism. Female 9.0 mm, with 40 eggs, egg size 0.65 mm on average.

Gnathopod 1 (figure 10A, D): propodus ovate, palm not very oblique, bearing nine spines on posterior margin. Gnathopod 2 (figure 11A, D): propodus subrectangular, palm transverse, bearing four slender spines on posterior corner. Pereopods 3 and 4 with long straight setae on posterior margin, less than those on male. Oostegites of pereopods 2–5 broad to elongate, with many long setae (figures 10B, C, 11B, C).

Habitat. Specimens of this species were found in a sump, the water coming from a small mural stream in a paper mill.

Remarks. Gammarus murarius n. sp. belongs to the Gammarus pulex - group ( Karaman and Pinkster, 1977). This species is similar to G. shanxiensis Barnard and Dai, 1988 , in the armature of antennae 1 and 2, and the shape of pereopods 5–7. Gammarus murarius can be distinguished from G. shanxiensis by the posterior margin of pereopod 3 with long curled setae, outer margin of outer ramus of uropod 3 with few plumose setae, palm of propodus of gnathopod 2 with one medial spine ( G. shanxiensis with two medial palmar spines).

Gammarus murarius differs from G. lacustris Sars, 1863 (widespread in the northern hemisphere), in not very acute epimeral plates 2 and 3, and posterior margin of pereopod 3 with long curled setae.