Gammarus martensi, 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 : 2749-2756

Gammarus martensi n. sp.

(figures 12–16)

Material examined. One male (HOLOTYPE), Taibaishan Mt (33.9 ‡ N, 107.7 ‡ E), Shaanxi Province, 25 June 1997, collected by J. Martens and P. Jaeger. Nineteen males, eight females and one juvenile (PARATYPES), the same collection data .

Etymology. This new species is named in honour of the collector, Prof. Dr J. Martens (Institute for Zoology, Johannes Gutenberg University, Mainz, Germany).

Diagnosis. Flagellum of antenna 2 bearing flag-like brush of setae on inner surface (figure 13F, H). Pereopods 3 and 4 with long straight setae on posterior margins (figure 14D, E), merus and carpus of pereopods 5–7 with three or four groups of spines accompanied by setae on both margins (figure 14A–C). Article 2 of outer ramus of uropod 3 shorter than adjacent spines; inner ramus more than half of article 1 of outer ramus (figure 15C). Urosomites 1–3 with long setae accompanied by spines dorsally (figure 12B, C).

Description. Male (holotype, IZCAS-I-A0043) 12.0 mm. Eyes oval (figure 12A). Inferior antennal sinus deep (figure 12A). Antenna 1 (figure 13E, G): peduncular articles 1–3 length ratio 1:0.72:0.44, bearing distal setae; flagellum with 29 articles; accessory flagellum with four articles. Antenna 2 (figure 13F, H): peduncular article 3 with distal setae, article 4 about as long as article 5, both with three to four groups of short setae along anterior and posterior margins; flagellum with 13 articles, bearing a flag-like brush of setae on inner surface, calceoli present.

Left mandible (figure 12D): incisor with five teeth; lacinia mobilis with four dentitions; article 3 a little shorter than article 2, article 2 bearing 13 setae, article 3 with four A-setae on outer face, three B-setae on inner face, a row of D-setae, four E-setae. Right mandible (figure 12I): incisor with four teeth; lacinia mobilis bifurcate, with many small teeth. Lower lip (figure 12F): inner plate absent. Maxilla 1 (figure 12G, J): inner plate bearing 13 plumose setae; outer plate bearing 11 serrated spines; article 2 of left palp bearing seven sharp spines and four stiff setae; article 2 of right palp bearing seven blunt spines and one seta. Maxilla 2 (figure 12K): inner plate bearing a diagonal row of 13 setae. Maxilliped (figure 12H): inner plate with three apical spines and one subapical spine; article 4 of palp unguiform.

Coxal plates 1–3 subrectangular (figures 13A, B, 14D), with two setae on anterior corner and one short seta on posterior corner; coxal plate 4 excavated (figure 14E), bearing two setae on anterior corner and five setae on posterior margin; coxal plates 5–7 shallow (figure 14A–C), bearing three or four setae on posterior corner. Coxal gills of pereopods 2–7 sac-like.

Gnathopod 1 (figure 13B, D): palm of propodus oblique, bearing one medial spine, with nine spines on posterior margin and four spines on inner surface; dactylus with one seta on outer margin and one seta at hinge of nail. Gnathopod 2 (figure 13A, C): palm of propodus transverse, bearing one medial spine, two spines on inner margin and two spines on outer margin.

Pereopods 3–4 with long straight setae on posterior margin (figure 14D–F), dactylus bearing one seta at joint of nail and one seta on outer margin.

Pereopods 5–7 similar (figure 14A–C, G). Anterior margin of bases bearing several setae and about eight spines; posterior margin nearly straight on pereopod 5, pinched distally on pereopod 6, processed on pereopod 7, with about 12 short setae; inner surface of pereopod 7 with two setae. Merus and carpus with three or four groups of spines accompanied by setae along anterior and posterior margins, setae longer than spines. Dactylus bearing one seta on outer margin, one seta and one setule at joint of nail.

Epimeral plates 1–3 not very acuminate (figure 15A), posterior margin bearing two to three short setae. Epimeral plate 1 with 12 setae on anterior ventral margin; epimeral plate 2 with two spines on ventral margin and one submarginal spine; epimeral plate 3 with four spines on ventral margin. Pleopods 1–3 subequal (figure 15D–F), peduncle with some setae, bearing two retinaculae accompanied by two or three setae, rami armed with plumose setae.

Urosomites 1–3 with long setae accompanied by spines dorsally (figure 12B, C). Uropod 1 (figure 15H): peduncle bearing one basofacial spine, five spines on outer margin and three spines on inner margin; outer and inner ramus with marginal spines. Uropod 2 (figure 15G): peduncle bearing three spines on each side; inner ramus a little longer than outer ramus, bearing two spines on outer margin and one spine on inner margin. Uropod 3 (figure 15C): peduncle with one spine dorsally and four spines distally; inner ramus 0.75 times as long as article 1 of outer ramus, bearing two marginal and two distal spines; article 1 of outer ramus bearing three pairs of spines on outer margin and four distal spines, article 2 shorter than adjacent spines; both rami densely covered with plumose setae.

Telson cleft (figure 15B), bearing two or three distal spines, one basolateral spine and one medial spine accompanied by long setae.

Dimorphism. Female 10.1 mm, with 22 eggs, egg size 0.8 mm on average.

Gnathopod 1 (figure 16B): propodus with long straight setae, palm oblique, with six spines on posterior corner. Gnathopod 2 (figure 16A): palm of propodus truncate, with four spines on posterior corner. Uropod 3 (figure 16G): inner ramus about 0.61 times as long as article 1 of outer ramus, article 2 of outer ramus shorter than adjacent spines, both rami with plumose setae. Telson cleft (figure 16C), each lobe with two or three distal spines and one facial spine accompanied by some setae.

Oostegites of pereopods 2–5 progressively smaller, bearing many long setae.

Habitat. Individuals of this species were found beneath humus, on the south flank of Taibaishan Mt, primary broad-leaved forest, altitude 2500–2600 m. Taibaishan Mt is the main peak of the Qinling Mountains.

Remark. Gammarus martensi n. sp. is similar to G. pulex ( Linnaeus, 1758) in the flagellum of antenna 2 with flag-like setae and the shape of gnathopods 1 and 2. This species differs from G. pulex in posterior margins of pereopods 3 and 4 with long straight setae; anterior margins of pereopods 5–7 with groups of spines, accompanied by setae, setae longer than spines; urosomites 1–3 with long dorsal setae.

Gammarus martensi can be distinguished from G. shenmuensis by the dissimilar gnathopods 1 and 2 and propodus palm with one medial spine; and from G. murarius by the flagellum of antenna 2 with flag-like setae.