Gammarus sobaegensis Uéno, 1966

Figures 12–15

Gammarus (Rivulogammarus) pulex sobaegensis Uéno, 1966: 525, figs. 14–18. Gammarus sobaegensis: Lee & Kim, 1980: 47, figs. 2–8.

Gammarus sobaegensis sobaegensis: Karaman, 1984: 143.

Material examined. NIBRIV0000282451, male (11.5 mm, 6 slides), NIBRIV00002824512, male (11.5 mm, 6 slides), NIBRIV00002824513, female (9.8 mm, 4 slides), Sannae-myeon (35˚53′28″N, 127˚47′24″E), Namwon-si, Jeonbuk, Korea, collected by K. Tomikawa, J. Kim, and H. Y. Soh on 11 November 2012. NIBRIV00002824514, male (9.5 mm, 6 slides), Baegunsan (35˚2′N, 127˚35′E), Korea, collected by K. Tomikawa and H. Y. Soh on 11 November 2012.

Description of male (NIBRIV0000282451). Body not carinate. Head shorter than pereonites 1 and 2 combined, rostrum short, antennal sinus rounded, eye elliptical shape. Postero-dorsal margins of pleonites 1–3 (Fig. 14 J–L) with numerous setae. Epimeral plates 1–3 (Fig. 14 C–E) with 5, 9, and 6 setae on respective posterior margins; anteroventral to ventral margin of plate 1 with setae; plate 2 with setae on anteromedial face, ventral margin with 4 robust setae; anteromedial face of plate 3 with setae, ventral margin with 4 robust setae. Urosomites 1–3 (Fig. 14 M–O) with 4, 4, and 2 robust setae on respective postero-dorsal margins.

Antenna 1 (Fig. 12 A): length 1.7 × antenna 2; peduncular articles 1–3 with length ratio of 1.0: 0.7: 0.4; peduncular article 1 with slender seta on outer surface, inner and outer surfaces setulose; peduncular article 2 length 2.2 × width, bering 2 clusters of setae on inner surface and 1 cluster and 2 pairs of setae on outer surface, both surfaces setulose; peduncular article 3 with 2 short setae on inner surface; accessory flagellum 5-articulate; primary flagellum 39-articulate, calceoli absent, aesthetascs (Fig. 12 B) present.

Antenna 2 (Fig. 12 C): peduncular article 1 with 6 setae distally; peduncular article 4 slightly shorter than article 5, length 2.8 × width, anterior margin with 3 clusters and 1 pair of setae and single seta, posterior margin with 7 clusters of setae and single seta, length of longest seta on posterior margin 1.1 × width of peduncular article 4, inner surface with 8 clusters of setae and single seta, outer margin with single seta and short setae; peduncular article 5 length 5.1 × width, anterior margin with 4 clusters and 1 pair of setae, posterior margin with 6 clusters and 2 pairs of setae and single seta, length of longest seta on posterior margin 1.7 × width of peduncular article 5, inner surface with 8 clusters of setae and single seta, outer surface with 2 clusters of setae and short setae; flagellum 15- articulate, calceoli absent.

Mouthparts. Upper lip (Fig. 12 D) with fine setae on rounded ventral margin. Lower lip (Fig. 12 E) with broad outer lobes, inner lobes indistinct. Mandibles (Fig. 12 F–H) with left and right incisors 5 and 4-dentate, respectively; left lacinia mobilis 4-dentate, right one bifid, bearing small teeth; accessory setal row consisting of weakly pectinate setae; palp 3-articulate with length ratio of 1.0: 3.0: 2.3, article 1 lacking setae, article 2 with 29 setae on ventral margin and 1 seta on subdorsal margin, article 3 with 1 cluster of A-setae, 2 clusters of B-setae, 22 D-setae, and 4 E-setae. Maxilla 1 (Fig. 12 I, J) with 15 plumose setae on medial margin of inner plate, inner surface of plate setulose; outer plate subrectangular, with 11 serrate robust setae apically; palp 2-articulate, exceeding tip of outer plate, article 1 short and lacking marginal setae, article 2 with 8 robust and 3 slender setae apically. Maxilla 2 (Fig. 12 K) with oblique setal row consisting of 16 plumose setae. Maxilliped (Fig. 12 L) with inner plate slightly exceeding palp article 1, bearing 3 nodular robust setae apically; outer plate with both apical and medial setae, including some robust and some plumose setae; palp 4-articulate, article 2 with inner marginal and submarginal rows of setae, article 3 curved, article 4 with medial setae.

Gnathopod 1 (Fig. 13 A, B): coxa subrectangular, anteroventral and posteroventral corners with 2 setae, respectively; basis with long setae on anterior and posterior margins; carpus length 0.7 × propodus, setae on anterodistal corner much shorter than width of carpus; propodus powerful, length 1.7 × width, tapering distally, palmar margin shallowly concave, anterior margin with 3 clusters of setae, posterior margin with 11 robust setae; dactylus curved inward, exceeding half of propodus.

Gnathopod 2 (Fig. 13 C, D): coxa slightly longer than coxa 1, slightly tapering distally, bearing 4 setae on anteroventral margin and seta on posteroventral corner; anterior and posterior margins of basis with long setae; carpus length 0.9 × propodus, setae on anterodistal corner longer than width of carpus; propodus length 1.9 × width, anterior and posterior margins almost parallel, anterior margin with 6 clusters of setae and single seta, palmar margin shallowly concave, palmar corner with 5 robust setae; dactylus curved inward.

Pereopod 3 (Fig. 13 E): coxa similar to coxa 2; basis length 3.4 × width, anterior margin with 2 pairs of setae and 7 setae, posterior margin with 3 clusters of setae and 5 setae; merus, carpus, propodus, and dactylus in length ratio of 1.0: 0.6: 0.6: 0.2, anterior margin of merus with 2 clusters of setae, posterior margin of merus with 5 clusters of straight setae and single straight seta, longest seta on posterior margin 1.9 × width of merus; posterior margin of carpus with 3 clusters of straight setae; propodus with 1 seta on anterior margin, 3 clusters of setae on posterior margin.

Pereopod 4 (Fig. 13 F): coxa expanded with posterior concavity, anteroventral corner and posterior margin with 2 and 9 setae, respectively; basis length 3.4 × width, anterior margin with 1 cluster of setae and 4 setae, posterior margin with 3 clusters of setae and 4 setae; merus, carpus, propodus, and dactylus in length ratio of 1.0: 0.7: 0.7: 0.3, anterior margin of merus with 2 clusters of setae, posterior margin of merus with 4 clusters of straight setae and single straight seta, longest seta on posterior margin 1.0 × width of merus; posterior margin of carpus with 2 clusters of straight setae and single straight seta; propodus with 2 clusters of setae and single robust seta on posterior margin.

Pereopod 5 (Fig. 13 G): coxa bilobed, anterior lobe without setae, posterior margin of posterior lobe with 2 setae; anterior margin of basis with pair of setae, 3 single setae, and 8 robust setae accompanied by short setae, posterior margin with 16 short setae, posterodistal lobe developed; merus, carpus, propodus, and dactylus in length ratio of 1.0: 0.9: 1.0: 0.3, anterior margins of merus, carpus, and propodus with robust setae and slender setae, posterior margins of them with robust setae accompanied by short setae and slender setae; dactylus with 2 short setae on anterior margin and penicillate seta on posterior margin.

Pereopod 6 (Fig. 14 A): coxa bilobed, anterior lobe without setae, ventral to posterior margin of posterior lobe with 4 setae; articles longer than those of pereopod 5; basis with pair of setae, 2 short robust setae, and 5 robust setae accompanied by short setae on anterior margin, posterior margin with 19 short setae, posterodistal lobe of basis weakly developed; merus, carpus, propodus, and dactylus in length ratio of 1.0: 1.1: 1.1: 0.3, anterior margins of merus, carpus, and propodus with robust setae and slender setae, posterior margins of them with robust setae accompanied by short setae and slender setae; dactylus with 2 short setae on anterior margin and penicillate seta on posterior margin.

Pereopod 7 (Fig. 14 B): ventral margin of coxa shallowly concave; basis with 2 pairs of setae and 6 robust setae accompanied by short setae on anterior margin, 18 short setae on posterior margin, posterodistal lobe of basis not developed; merus, carpus, propodus, and dactylus in length ratio of 1.0: 1.2: 1.1: 0.3, anterior margins of merus, carpus, and propodus with robust setae and slender setae, posterior margins of them with robust setae accompanied by short setae and slender setae; dactylus with 2 short setae on anterior margin and penicillate seta on posterior margin.

Coxal gills present on gnathopod 2 and pereopods 3–7.

Pleopods: peduncle with meny setae, innerdistal corner with 2 retinacula, inner basal margin of inner ramus with bifid plumose setae (clothes-pin setae).

Uropods. Uropod 1 (Fig. 14 F): peduncle with 2 basofacial robust setae, 3 lateral and 4 medial robust setae marginally; outer ramus length 0.7 × peduncle, bearing 2 robust setae on respective lateral and medial margins; inner ramus as long as outer ramus, lateral and medial margins with 2 and 3 robust setae, respectively, ventral margin with 2 slender setae. Uropod 2 (Fig. 14 G): peduncle with 3 lateral and 3 medial robust setae marginally; outer ramus length 0.8 × peduncle, lateral and medial margins with 3 and 1 robust setae, respectively; inner ramus length 1.2 × outer ramus, bearing 2 and 5 robust setae on respective lateral and medial margins. Uropod 3 (Fig. 14 H): peduncle length 1.6 × width, with robust and slender setae; inner ramus 1-articulate, length 2.1 × peduncle and 0.8 × outer ramus, both margins with plumose setae; outer ramus 2-articulate, lateral margin of article 1 with simple setae only, inner margin with plumose setae, article 2 short, length 0.1 × article 1.

Telson (Fig. 14 I): length 1.1 × width, cleft for 76% of length; each lobe tapering distally, with several facial setae; apex truncate, with robust setae and slender setae longer than robust seta.

Description of female (NIBRIV00002824513). Antenna 1 (Fig. 15 A): peduncular articles 1–3 with length ratio of 1.0: 0.8: 0.5,; peduncular article 2 length 3.0 × width. Antenna 2 (Fig. 15 B): peduncular article 4 length 0.8 × article 5, length 3.1× width, posterior margin with 5 clusters of setae and 2 single setae; peduncular article 5 length 4.8 × width, posterior margin with 6 clusters of setae and 2 single setae.

Gnathopod 1 (Fig. 15 C): anterior margins of carpus and propodus with long setae, setae on anterodistal corner of carpus slightly shorter than width of carpus; propodus not powerful, length 1.7 × width, palmar corner with 3 robust setae; dactylus short, not exceeding half of propodus. Gnathopod 2 (Fig. 15 D): anterior margins of carpus and propodus with long setae; carpus as long as propodus, setae on anterodistal corner slightly shorter than width of carpus; propodus length 2.3 × width, anterior margin with 5 clusters of setae, palmar corner with a robust seta. Oostegites on gnathopod 2 and pereopods 3–5.

Uropod 3 (Fig. 15 E): peduncle length 1.8 × width; inner ramus length 1.6 × peduncle and 0.7 × outer ramus; article 2 of outer ramus length 0.2 × article 1.

Variation. Maxilla 1 bears 15–18 plumose setae on the medial margin of the inner plate. Maxilla 2 bears 14–16 facial setae of the inner plate.

Distribution. The species is distributed in the southern part of the Korean Peninsula (Uéno 1966; Lee & Kim 1980; this study).

Remarks. Gammarus sobaegensis was described by Uéno (1966) based on the specimens collected from caves in the Korean Peninsula. Our materials agree with the original description of G. sobaegensis. Lee & Kim (1980) intensively carried the taxonomic study of the genus Gammarus in Korea, and revealed that G. sobaegensis is widely distributed in Korea. Since this species is morphologically very similar to G. nipponensis, Karaman (1986) suggested that G. sobaegensis is possible synonym with G. nipponensis. However, our detailed examination revealed that the former is distinguished from the latter by the following features (features of G. nipponensis are in parentheses): 1) dorsal margins of pleonites 1–3 with numerous setae (four setae), 2) anterodistal setae on the carpus of male gnathopod 2 longer than the width of the carpus (shorter), 3) longest seta on posterior margin of merus of pereopod 3 2 × width of merus (1.4), and 4) the article 2 of the outer ramus of uropod 3 longer than terminal robust setae on the article 1 (shorter). We also found that these two species are genetically divergent at species level in the nuclear 28S rRNA and the mitochondrial COI genes.

Karaman (1986) recorded G. sobaegensis from the cave of Akiyoshi-do, Yamaguchi Prefecture, Japan. Unfortunately, we could not examine specimens from the cave. Further study is needed to clarify the occurrence of the species in Japan.