Gammarus rivalis, HOU & LI & LI, 2013

HOU, ZHONGE, LI, JUNBO & LI, SHUQIANG, 2013, Ten new Gammarus species (Crustacea: Amphipoda: Gammaridae) from Yunnan-Guizhou Plateau, China , Zootaxa 3687 (1), pp. 1-95 : 68-76

publication ID	https://doi.org/ 10.11646/zootaxa.3687.1.1
publication LSID	lsid:zoobank.org:pub:193BA226-D0D0-42C9-9815-639E8E48EF7A
DOI	https://doi.org/10.5281/zenodo.10540398
persistent identifier	https://treatment.plazi.org/id/5D2BDE76-FF8E-716A-FF54-FB64FE3CF8C9
treatment provided by	Felipe
scientific name	Gammarus rivalis
status	sp. nov.

Treatment

Gammarus rivalis sp. nov.

Figs 4B View FIGURE 4 , 48–53 View FIGURE 48 View FIGURE 49 View FIGURE 50 View FIGURE 51 View FIGURE 52 View FIGURE 53

Material examined. Holotype: male (IZCAS-I-A1079-1), 11.2 mm, from the farmland near by Tangzi Town (100.25°E, 25.42°N), altitude 1,904 m, Xundian Country, Yunnan Province, China, February 19, 2010, collected by L. Lin. GoogleMaps Paratype: 1 female (IZCAS-I-A1079-2), 9.7 mm, same data as holotype GoogleMaps .

Etymology. The specific name is from Latin rivalis (of a brook), in reference to the habitat of this species; adjective.

Diagnosis. 4 th and 5 th article of antenna II peduncle with 7–9 clusters of lateral and medial long setae; propodus of gnathopod I larger than gnathopod II; basis of pereopod V subrounded; urosome segments I and II with no armament or with few tiny setae; inner ramus of uropod III slightly longer than outer ramus, with few plumose setae along lateral margins, terminal article very small. Female merus to propodus of pereopods V–VII with more setae than those of male.

Description of male. Holotype (IZCAS-I-A1079-1), male 11.2 mm ( Fig. 4B View FIGURE 4 ).

Head ( Fig. 48A View FIGURE 48 ): eyes reniform, 1.8 times as long as wide, inferior antennal sinus deep, lateral cephalic lobe nearly straight.

Antenna I ( Fig. 48B, C View FIGURE 48 ): 1 st to 3 rd article of peduncle in length ratio 1.0: 0.9: 0.6, with setae on distal corner; flagellum with 31 articles, 3 rd to 29 th article with aesthetascs; accessory flagellum with 4 articles; both primary and accessory flagella with short distal setae.

Antenna II ( Fig. 48D, E View FIGURE 48 ): about 0.7 times as long as antenna I, 3 rd to 5 th article of peduncle in length ratio 1.0: 2.9: 3.1, 4 th and 5 th article of peduncle with 7–9 clusters of long lateral and medial setae; flagellum with 13 articles and 1 tiny distal article, with long setae along dorsal and ventral margins; calceoli absent.

Upper lip ( Fig. 48F View FIGURE 48 ): ventral margin rounded, bearing minute setae.

Mandible ( Fig. 48H, I View FIGURE 48 ): left mandible incisor with 5 teeth; lacinia mobilis with 4 teeth; 1 st to 3 rd article of palp with length ratio 1.0: 4.0: 3.0, 2 nd article of palp with 13 marginal setae, 3 rd article with 3 A-setae, 4 clusters of Bsetae, 22 D-setae and 7 E-setae apically; incisor of right mandible with 4 teeth, lacinia mobilis bifurcate, with small teeth.

Lower lip ( Fig. 48G View FIGURE 48 ): inner lobes lacking, outer lobes covered with thin setae.

Maxilla I ( Fig. 48J, K View FIGURE 48 ): asymmetrical, left inner plate with 14 plumose setae on medial margin; outer plate with 11 robust serrated apical spines, each spine with small teeth; 2 nd article of palp with 7 slender spines and 2 stiff setae apically; 2 nd article of right palp with 4 stout spines, 1 stiff seta and 1 slender spine.

Maxilla II ( Fig. 48L View FIGURE 48 ): inner plate with 10 plumose facial setae in an oblique row; inner and outer plates with long setae apically.

Maxilliped ( Fig. 48M View FIGURE 48 ): inner plate with 1 subapical and 3 stout apical spines, some plumose setae along lateral margin; outer plate bearing a row of blade spines and 3 plumose setae apically; 4 th article of palp hooked, with a group of setae at hinge of unguis.

Gnathopod I ( Fig. 49A, C View FIGURE 49 ): coxal plate bearing 7 setae and 2 setae on anterior and posterior margins, respectively; basis with setae on anterior and posterior margins; carpus 1.1 times as long as wide, about 0.7 times as long as propodus, posterior margin bearing short setae; propodus oval, palm with 2 medial spines and 13 spines on posterior margin and surface; dactylus with 1 seta on outer margin.

Gnathopod II ( Fig. 49B, D View FIGURE 49 ): coxal plate bearing 3 setae and 1 seta on anterior and posterior margins; basis with long setae on anterior and posterior margins, posterodistal corner with short setae; carpus 2.1 times as long as wide, about 0.9 times as long as propodus, with parallel margins, bearing 7 clusters of setae along ventral margin, 2 clusters of setae on dorsal margin; propodus subrectangular, palm margin with 1 medial spine and 4 spines on lateral posterodistal corner; dactylus with 1 seta on outer margin.

Pereopod III ( Fig. 50A, F View FIGURE 50 ): coxal plate bearing 3 setae and 1 seta on anteroventral and posterior margins; basis elongate, with setae along anterior and posterior margins; merus with 5 clusters of setae on posterior margin and 1 spine on anterior margin, anterodistal corner with 1 spine accompanied by setae; carpus and propodus with groups of spines accompanied by setae on posterior margin; dactylus with 1 plumose seta on posterior margin, and 2 setae at hinge of unguis.

Pereopod IV ( Fig. 50B, G View FIGURE 50 ): coxal plate excavated, bearing 5 setae on anterior margin and 8 setae on posterior margin; basis with some simple setae along anterior and posterior margins; merus with 5 clusters of setae on posterior margin and 1 spine on anterior margin, anterodistal with 1 spine accompanied by some setae; carpus and propodus with groups of spines accompanied by setae on posterior margin; dactylus with 1 plumose seta on anterior margin, and 2 setae at hinge of unguis.

Pereopod V ( Fig. 50C, H View FIGURE 50 ): coxal plate bearing 1 seta on anterior margin; basis subrounded, with 7 spines on anterior margin, anterodistal corner with 2 spines, posterior margin with a row of 11 setae; merus with 4 clusters of setae on anterior margin; carpus and propodus with groups of spines accompanied by setae on anterior margin, propodus with 1 group of setae and 1 spine on posterior margin; dactylus with 1 plumose seta on posterior margin, and 2 setae at hinge of unguis.

Pereopod VI ( Fig. 50D, I View FIGURE 50 ): coxal plate bearing 2 setae on posterior margin; basis elongate, with 3 spines on anterior margin, anterodistal corner with 2 spines, posterior margin dwindling distally, with a row of 12 setae; merus to propodus with groups of spines accompanied by setae on anterior margin, propodus with 3 groups of setae on posterior margin; dactylus with 1 plumose seta on posterior margin, and 2 setae at hinge of unguis.

Pereopod VII ( Fig. 50E, J View FIGURE 50 ): coxal plate bearing 5 setae on posterior margin; basis expanded, posterior margin weakly narrowed distally, anterior with 5 spines, anterodistal corner with 2 spines, posterior with a row of 14 setae; merus to propodus with groups of spines accompanied by setae on anterior margin, propodus with 1 spine accompanied by 1 seta on posterior margin; dactylus with 1 plumose seta on posterior margin, and 2 setae at hinge of unguis.

Coxal gills: coxal gill of gnathopod II and gills of pereopods III–V a little shorter than bases; gill of pereopod VI more than half the length of basis; gill of pereopod VII smallest, less than half of basis.

Epimeral plates ( Fig. 49E–G View FIGURE 49 ): plate I ventrally rounded, bearing 7 setae on anteroventral margin and 7 setae on posterior margin; plate II with 2 spines on ventral margin and 7 setae on posterior margin, posterodistal corner subacute; plate III with 2 spines on ventral margin and 8 setae on posterior margin, posterodistal corner subacute.

Pleopods I–III ( Fig. 51C–E View FIGURE 51 ): similar, peduncle with 1–2 retinacula accompanied by 1–2 setae; outer ramus slightly longer than inner ramus, both rami fringed with plumose setae.

Urosome ( Fig. 51A, B View FIGURE 51 ): dorsally flat, urosome segments I and II without or with few tiny setae on dorsal margin. Urosome segment III with 1 spine accompanied by 1 seta on each side and 2 clusters of 2 setae on dorsal margin.

Uropods I–III ( Fig. 51F–H View FIGURE 51 ): uropod I peduncle without basofacial spine, with 1 spine on outer and inner margins, with 2 and 1 spine on outer and inner corners; inner ramus with 1 spine on inner margin; outer ramus with 1 spine on outer and inner margins; both rami with 5 terminal spines. Uropod II short, peduncle bearing 1 and 2 spines on outer and inner margins, with 2 and 1 distal spine on outer and inner corners; inner ramus with 1 and 2 spines on outer and inner margins; outer ramus with 1 spine on outer margin; both rami with 5 terminal spines. Uropod III peduncle with 4 distal spines; inner ramus about 3 times as long as peduncle, slightly longer than outer ramus, both margins with 3 spines accompanied by 1 plumose seta, bearing 2 apical spine and simple setae; 1 st article of outer ramus with 1 and 2 spines accompanied by long simple setae on outer margin, inner margin with 4 clusters of 1 simple seta and 1 plumose seta; terminal article very small, with some simple setae apically.

Telson ( Fig. 51I View FIGURE 51 ): deeply cleft, as long as wide, both lobes with 2 clusters of 1 simple setae accompanied by 1 plumose seta on dorsolateral margins and 2 apical spines.

Description of female. Paratype (IZCAS-I-A1079-2), 9.7 mm.

Gnathopod I ( Fig. 52A, C View FIGURE 52 ): coxal plate bearing 5 fine setae and 3 setae on anterior and posterior margins, respectively; basis with setae on anterior and posterior margins; propodus oval, palm with 8 spines on posterior margin.

Gnathopod II ( Fig. 52B, D View FIGURE 52 ): coxal plate bearing 4 fine setae and 1 seta on anterior and posterior margins; basis with setae on anterior and posterior margins, posterodistal corner with short setae; propodus subrectangular, palm margin with 7 spines on posterodistal corner, bearing simple setae along anterior and posterior margins; dactylus with 1 seta on outer margin.

Pereopods III and IV ( Fig. 53A–B, F–G View FIGURE 53 ): basis and merus with more setae on posterior margins than those of male.

Pereopods V–VII ( Fig. 53C–E, H–J View FIGURE 53 ): merus to propodus with more setae than those of male.

Uropods I–III ( Fig. 51J–L View FIGURE 51 ): uropod I peduncle without basofacial spine, with 2 spines and 1 spine on outer and inner margins, with 2 and 1 spine on outer and inner corners; both rami with 2 spines on inner margins and 5 terminal spines. Uropod II similar to that of male. Uropod III peduncle with 5 distal spines; inner ramus 1.4 times as long as peduncle, reaching 0.9 times the length of outer ramus, with 3 plumose setae on lateral margin; 1 st article of outer ramus with 2 pairs of spines accompanied by setae on outer margin, inner margin with 2 clusters of 1 simple seta accompanied by 1 plumose seta; terminal article tiny, with some simple setae apically.

Telson ( Fig. 52I View FIGURE 52 ): cleft, similar to those of male.

Oostegite ( Fig. 52E–H View FIGURE 52 ): oostegite of gnathopod II broad, with marginal setae, oostegites of pereopods III and IV elongate, oostegite of pereopod V smallest.

Variability. Inner ramus of uropod III nearly the same length of outer ramus or a little longer than outer ramus; urosome segments I and II with no armature or with few tiny setae.

Habitat. The species was found in a small brook beside the farmland.

Remarks. Gammarus rivalis sp. nov. is similar to G. glabratus Hou & Li, 2002 . It can be distinguished from G. glabratus by the following characters ( G. glabratus in parentheses): 4 th and 5 th article of antenna II peduncle with 7–9 clusters of lateral and medial long setae (short setae); propodus of gnathopod I apparently larger than that of gnathopod II (a litter bigger); inner ramus of uropod III a litter longer than outer ramus, inner margins of both rami with a few plumose setae (inner ramus a litter shorter than outer ramus, inner margins of both rami with more plumose setae); pereopods V–VII of female with clusters of setae along merus to carpus margins (clusters of spines accompanied by few setae).