Gammarus silendus, 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 : 76-85

publication ID	https://doi.org/ 10.11646/zootaxa.3687.1.1
publication LSID	lsid:zoobank.org:pub:193BA226-D0D0-42C9-9815-639E8E48EF7A
persistent identifier	https://treatment.plazi.org/id/5D2BDE76-FF86-7175-FF54-F8D1FDC6FDAD
treatment provided by	Felipe
scientific name	Gammarus silendus
status	sp. nov.

Treatment

Gammarus silendus sp. nov.

Figs 4C View FIGURE 4 , 54–59 View FIGURE 54 View FIGURE 55 View FIGURE 56 View FIGURE 57 View FIGURE 58 View FIGURE 59

Material examined. Holotype: male (IZCAS-I-A1092-1), 11.4 mm, from the Dixian Cave nearby Guanping

Village (106.21°E, 28.29°N), altitude 1,280 m, Donghuang Town , Xishui County, Guizhou Province, China, May 2, 2010, collected by Y. Lin and Q. Zhao. Paratype: female (IZCAS-I-A1092-2), 11.9 mm, same data as holotype GoogleMaps .

Etymology. The specific name is from Latin silendus (secret), in reference to the type locality; adjective.

Diagnosis. Eyes absent; 2 nd article of right palp of maxilla I with 7 stout spines; inner plates of maxilla I and II with 20 and 17 plumose setae; propodus palm of gnathopods I and II oval; inner ramus of uropod III reaching about 0.9 times the length of outer ramus, 2 nd article of outer ramus very short; epimeral plates II and III with 3–4 spines on ventral margin, posterodistal corners blunt; urosome segment I with 2 clusters of 1 spine accompanied by 2 setae on dorsal margin, but no lateral spines.

Description of male. Holotype (IZCAS-I-A1092-1), male 11.4 mm ( Fig. 4C View FIGURE 4 ).

Head ( Fig. 54A View FIGURE 54 ): eyes absent, inferior antennal sinus deep, lateral cephalic lobe nearly straight.

Antenna I ( Fig. 54B, C View FIGURE 54 ): 1 st to 3 rd article of peduncle in length ratio 1.0: 0.7: 0.4, with setae on distal corner; flagellum with 30 articles, 3 rd to 29 th article with aesthetascs; accessory flagellum with 5 articles; both primary and accessory flagella with short distal setae.

Antenna II ( Fig. 54D, E View FIGURE 54 ): about 0.7 times as long as antenna I, 3 rd to 5 th article of peduncle in length ratio 1.0: 2.6: 2.4, 4 th and 5 th article of peduncle with 9–10 clusters of short lateral and medial setae; flagellum with 13 articles and 1 tiny distal article, with setae along ventral margins; calceoli present in 1 st to 9 th article.

Upper lip ( Fig. 54F View FIGURE 54 ): ventral margin rounded, bearing minute setae.

Mandible ( Fig. 54H, I View FIGURE 54 ): left mandible incisor with 5 teeth; lacinia mobilis with 4 teeth, spine row with 7 pairs of plumose setae along lateral margin; 1 st to 3 rd article of palp in length ratio 1.0: 2.7: 2.6, 2 nd article of palp armed with 14 marginal setae, 3 rd article with 6 A-setae and 2 clusters of B-setae, 22 D-setae and 6 E-setae apically; incisor of right mandible with 4 teeth, lacinia mobilis bifurcate, with small teeth.

Lower lip ( Fig. 54G View FIGURE 54 ): inner lobes lacking, outer lobes covered with thin setae.

Maxilla I ( Fig. 54J, K View FIGURE 54 ): asymmetrical, left inner plate with 20 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 7 stout spines, 1 stiff seta and 1 slender spine.

Maxilla II ( Fig. 54L View FIGURE 54 ): inner plate with 17 plumose facial setae in an oblique row; inner and outer plates with long setae apically.

Maxilliped ( Fig. 54M View FIGURE 54 ): inner plate with 1 subapical and 3 stout apical spines, some plumose setae along ventral 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. 55A, C View FIGURE 55 ): coxal plate bearing 3 setae on anterior and posterior margins, respectively; basis with setae on anterior and posterior margins; carpus about 0.7 times as long as wide, about 0.6 times as long as propodus, posterior margin bearing short setae; propodus oval, palm evenly with 2 median spines and 17 spines on posterior margin and facial surface; dactylus with 1 seta on outer margin.

Gnathopod II ( Fig. 55B, D View FIGURE 55 ): coxal plate bearing 5 setae and 1 seta on anterior and posterior margins; basis with setae on anterior and posterior margins, posterodistal corner with short setae; carpus 1.5 times as long as wide, about 0.7 times as long as propodus, with parallel margins, bearing 8 clusters of setae along ventral margin and 2 clusters of setae on dorsal margin; propodus palm ovate, palm margin evenly with 2 median spines and 4 spines on posterodistal corner; dactylus with 1 seta on outer margin.

Pereopod III ( Fig. 56A, F View FIGURE 56 ): coxal plate bearing 6 setae and 2 setae on anteroventral and posterior margins; basis elongate, with setae along posterior margin; merus with 7 clusters of setae on posterior margin and 3 single spines on anterior margin; carpus and propodus with groups of spines accompanied by short setae on posterior margin; dactylus with 1 plumose seta on posterior margin, and 2 setae at hinge of unguis.

Pereopod IV ( Fig. 56B, G View FIGURE 56 ): coxal plate excavated, bearing 6 setae on anterior margin and 5 setae on posterior margin; basis with setae on posterior margin; merus with 1 spine accompanied by short setae and 5 clusters of setae on posterior margin, with 2 spines accompanied by short setae on anterior margin, anterodistal with 1 spine accompanied by 1 seta; carpus and propodus with groups of spines accompanied by short setae on posterior margins; dactylus with 1 plumose seta on anterior margin, and 2 setae at hinge of unguis.

Pereopod V ( Fig. 56C, H View FIGURE 56 ): coxal plate bearing 2 setae on posterior margin; basis with 3 setae and 7 spines on anterior margin, anterodistal corner with 2 spines accompanied by 1 seta, posterior margin 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 VI ( Fig. 56D, I View FIGURE 56 ): coxal plate bearing 2 setae on posterior margin; basis elongate, with 4 setae and 5 spines on anterior margin, anterodistal corner with 3 spines, posterior margin dwindling distally, with a row of 13 setae; merus to propodus with groups of spines accompanied by setae on anterior margin, propodus with 4 groups of setae on posterior margin; dactylus with 1 plumose seta on posterior margin, and 2 setae at hinge of unguis.

Pereopod VII ( Fig. 56E, J View FIGURE 56 ): coxal plate bearing 3 setae on posterior margin; basis expanded, posterior margin oval, anterior with 2 clusters of setae and 6 spines, anterodistal corner with 3 spines, posterior with a row of 13 setae, inner surface with 1 spine accompanied by 1 seta; merus to propodus with groups of spines accompanied by setae on anterior margin, propodus with 4 groups of setae 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 length of basis; gill of pereopod VII smallest, less than half of basis.

Epimeral plates ( Fig. 57A–C View FIGURE 57 ): plate I ventrally rounded, bearing 7 setae on anteroventral margin and 3 setae on posterior margin; plate II with 3 spines on ventral margin and 4 setae on posterior margin, posterodistal corner blunt; plate III with 4 spines on ventral margin, and 4 setae on posterior margin, posterodistal corner blunt.

Pleopods I–III ( Fig. 57E–G View FIGURE 57 ): similar, peduncles with 2 retinacula accompanied by 1–2 setae; outer ramus slightly shorter than inner ramus, both rami fringed with plumose setae.

Urosome ( Fig. 57D View FIGURE 57 ): dorsally flat. Urosome segment I with 2 clusters of 1 spine accompanied by 2 setae on dorsal margin. Urosome segment II with 3-1-1-2 spines accompanied by setae on dorsal margin. Urosome segment III with 2 spines accompanied by 1 seta on each side.

Uropods I–III ( Fig. 57H–K View FIGURE 57 ): uropod I peduncle with 1 basofacial spine, with 1 and 3 spines on inner and outer margins, with 2 and 1 spine on outer and inner corners; both rami with 1 spine on inner margins and 5 terminal spines. Uropod II short, peduncle bearing 1 spine on inner margin, with 1 distal spine on each corner; inner ramus with 1 spine on inner margin; outer ramus shorter than inner ramus; both rami with 5 terminal spines. Uropod III peduncle with 1 spine accompanied by 1 seta and 4 setae on surface, 4 distal spines accompanied by setae; inner ramus about 1.9 times as long as peduncle, reaching 0.9 times the length of outer ramus, with plumose setae on outer and inner margins, bearing 2 apical spines accompanied by setae; 1 st article of outer ramus with 2 pairs of spines on outer margin, both margins with plumose setae and few simple setae; terminal article vestigial.

Telson ( Fig. 57L View FIGURE 57 ): deeply cleft, 0.9 times as long as wide, both lobes with setae on dorsolateral margins, 3 and 2 apical spines accompanied by setae.

Description of female. Paratype (IZCAS-I-A1092-2), 11.9 mm.

Gnathopod I ( Fig. 58A, C View FIGURE 58 ): coxal plate bearing 4 setae and 1 seta on anterior and posterior margins, respectively; basis with setae on anterior and posterior margins; propodus oval, palm with 8 spines on posterior margin; dactylus with 1 seta on outer margin.

Gnathopod II ( Fig. 58B, D View FIGURE 58 ): coxal plate bearing 6 setae and 1 seta on anterior and posterior margins; basis with setae on anterior and posterior margins, posterodistal corner with short setae; propodus subrectangular, bearing setae along anterior and posterior margins, palm margin with 4 spines on posterodistal corner; dactylus with 1 seta on outer margin.

Pereopods III–VII ( Fig. 59 A–E View FIGURE 59 ): similar to those of male.

Uropods I–III ( Fig. 57M–O View FIGURE 57 ): uropod I peduncle with 1 basofacial spine, with 2 spines on outer margin, 2 and 1 spine on outer and inner corners; inner ramus with 1 spine on inner margin; both rami with 5 terminal spines. Uropod II with 1 distal spine on each corner; inner ramus with 1 spine on inner margin; both rami with 5 terminal spines. Uropod III peduncle with 1 spine accompanied by 2 setae on surface; inner ramus about 1.8 times as long as peduncle, reaching 0.9 times the length of outer ramus, with plumose setae on outer and inner margins, bearing 2 apical spines accompanied by setae; 1 st article of outer ramus with 2 single spines on outer margin, both margins with plumose setae and few simple setae; terminal article very short.

Telson ( Fig. 59F View FIGURE 59 ): deeply cleft, both lobes with setae on dorsolateral margins.

Oostegite ( Fig. 59G–J View FIGURE 59 ): oostegite of gnathopod II broad, oostegites of pereopods III and IV elongate, oostegite of pereopod V smallest.

Variability. The variability pattern is of the normal of G. pulex on the setation of pereopods III–VII, uropod III and telson lobes ( Karaman & Pinkster 1977).

Habitat. This species was found in a small pool in Dixian Cave, with water temperature 15ºC.

Remarks. Gammarus silendus sp. nov. is similar to G. xianfengensis Hou & Li, 2002 in: eyes absent and calceoli present. The new species can be distinguished from G. xianfengensis by the following characters ( G. xianfengensis in parentheses): 2 nd article of right palp in maxilla I with 7 stout spines, inner plates of maxilla I and II with 17–20 plumose setae (inner plates of maxilla I and II with 12–13 plumose setae); epimeral plates with 3–4 spines on ventral margin, posterodistal corners blunt (with 5–6 spines on ventral margin, posterodistal corners blunt or subacute); terminal article of uropod III very short (terminal article of uropod III distinct, but shorter than adjacent spines); urosome segment I with no lateral spines (with 1 lateral spine accompanied by setae on each side).

The new species can be distinguished from Sinogammarus troglodytes Karaman, 1995 by the following characters ( Sinogammarus troglodytes in parentheses): flagellum of antenna I with 30 articles (with 43 articles); 2 nd article of right palp in maxilla I with 7 stout spines (with 5 stout spines); 3 rd article of mandible palp with 1 group of A-setae and B-setae respectively (2 A-setae and 2 B-setae); posterior margin of bases of pereopods VI and VII oval (posterior margin narrowed distally).