Gammarus nipponensis Uéno, 1940

Tomikawa, Ko, Soh, Ho Young, Kobayashi, Norio & Yamaguchi, Aika, 2014, Taxonomic relationship between two Gammarus species, G. nipponensis and G. sobaegensis (Amphipoda: Gammaridae), with description of a new species, Zootaxa 3873 (5), pp. 451-476 : 463-468

Gammarus nipponensis Uéno, 1940

[Japanese name: Nippon-yokoebi] Figures 9–11

Gammarus pulex: Tattersall, 1922: 451 , pl. XX, figs. 19–21; Uéno, 1927: 365, fig. 6. Gammarus (Rivulogammarus) nipponensis Uéno, 1940: 81 , figs. 91–116; Uéno, 1941:461. Gammarus nipponensis: Karaman, 1984: 153 ; 1986: 83, figs. 1–3.

Gammarus sobaegensis: Karaman, 1986: 88 , figs. 4–6.

Material examined. NSMT-Cr 22728, male (10.0 mm, 6 slides), NSMT-Cr 22729, male (11.2 mm, 5 slides), NSMT-Cr 22730, female (9.1 mm, 4 slides), and NSMT-Cr 22731, 2 males and 2 females in ethanol vial, Kiyotaki (35˚2′27.8″N, 135˚39′24.9″E), Kyoto, Kyoto Prefecture, Japan, collected by K. Tomikawa and S. Tashiro on 10 December 2011.

Description of male (NSMT-Cr 22729). Body not carinate. Head shorter than pereonites 1 and 2 combined, rostrum short, antennal sinus rounded, eye elliptical shape. Pleonites 1–3 ( Fig. 11 D–F) with 4 setae on respective postero-dorsal margins. Epimeral plates 1–3 ( Fig. 11 A–C) with 4, 5, and 5 setae on respective posterior margins; anteroventral margin of plate 1 with many setae; ventral margins of plates 2 and 3 with 2 and 3 robust setae, respectively. Urosomites 1–3 ( Fig. 11 G–I) with 2 robust setae on respective postero-dorsal margins.

Antenna 1 ( Fig. 9 A): length 1.5 × antenna 2; peduncular articles 1–3 with length ratio of 1.0: 0.8: 0.5; peduncular article 1 with cluster of short setae on anterior margin and 2 setae on posterior margin, inner and outer surfaces setulose; peduncular article 2 length 3.0 × width, bearing cluster of setae and short setae on inner and outer surfaces, respectively; peduncular article 3 with 2 short setae on inner surface; accessory flagellum 4-articulate; primary flagellum 30-articulate, calceoli absent.

Antenna 2 ( Fig. 9 B): peduncular article 1 with pair of setae distally; peduncular article 4 slightly shorter than article 5, length 3.1 × width, anterior margin with 2 clusters of setae, posterior margin with single seta and 6 clusters of setae, length of longest seta 1.6 × width of peduncular article 4, inner surface with 5 clusters, 1 pair of setae and 2 seta, outer surface with cluster of setae and 2 short setae; peduncular article 5 length 5.4 × width, anterior submargin with 3 clusters of setae and pair of setae, posterior margin with 2 setae and 6 clusters of setae, length of longest seta on posterior margin 2.4 × width of peduncular article 5, inner surface with 8 clusters of setae and single seta, outer surface with cluster of setae and pair of short setae; flagellum 11-articulate, calceoli absent.

Mouthparts. Upper lip ( Fig. 9 C) with fine setae on rounded ventral margin. Lower lip ( Fig. 9 D) with broad outer lobes, inner lobes indistinct. Mandibles ( Fig. 9 E–G) with left and right incisors 5 and 4-dentate, respectively; left lacinia mobilis 4-dentate, right one indistinctly bifid, bearing small teeth; each accessory setal row consisting of weakly pectinate setae; palp 3-articulate with length ratio of 1.0: 2.7: 2.1, article 1 lacking setae, article 2 with 22 setae, article 3 with 1 cluster of A-setae, 2 clusters of B-setae, 27 D-setae, and 4 E-setae. Maxilla 1 ( Fig. 9 H, I) with 16 plumose setae on medial margin of inner plate, inner surface 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. 9 J) with oblique setal row consisting of 12 plumose setae. Maxilliped ( Fig. 9 K) with inner plate exceeding palp article 1, with 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. 9 L, M): coxa subrectangular, anteroventral and posteroventral corners each with 1 seta; 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 1.9 × width, weakly tapering distally, anterior margin with 2 clusters of setae, palmar margin shallowly concave, posterior margin with 15 robust setae; dactylus curved inward, exceeding half of propodus.

Gnathopod 2 ( Fig. 9 N, O): coxa slightly longer than coxa 1, anteroventral and posteroventral corners each with 1 seta; anterior and posterior margins of basis with long setae; carpus length 0.8 × propodus, setae on anterodistal corner shorter than width of carpus; propodus length 2.1 × width, anterior and posterior margins almost parallel, anterior margin with 5 clusters of setae, palmar margin shallowly concave, palmar corner with 5 robust setae; dactylus curved inward.

Pereopod 3 ( Fig. 10 A): coxa with anteroventral seta; basis long, length 3.8 × width, anterior margin with 8 setae, posterior margin with cluster of setae and 6 setae; merus, carpus, propodus, and dactylus in length ratio of 1.0: 0.7: 0.7: 0.2, anterior margin of merus with pair of setae and single short seta, posterior margin of merus with 4 clusters of straight setae and single seta, longest seta on posterior margin 1.4 × width of merus; posterior margin of carpus with 3 clusters of straight setae; propodus with 3 clusters of setae on posterior margin.

Pereopod 4 ( Fig. 10 B): coxa expanded with posterior concavity, anteroventral corner and posterior margin with 2 and 7 setae, respectively; basis length 3.8 × width, anterior margin with 2 pair of setae and single seta, posterior margin with 3 clusters and 1 pair of setae and 3 setae; merus, carpus, propodus, and dactylus in length ratio of 1.0: 0.7: 0.7: 0.2, anterior margin of merus with cluster of setae and single seta, posterior margin of merus with 4 clusters and 1 pair of setae, longest seta on posterior margin 1.1 × width of merus; posterior margin of carpus with 2 clusters of straight setae; propodus with 3 clusters of setae on posterior margin.

Pereopod 5 ( Fig. 10 C): coxa bilobed, anterior lobe with 1 seta, posterior margin of posterior lobe with 3 setae; anterior margin of basis with 6 robust and 2 short robust setae accompanied by short setae, posterior margin with 14 short setae (4 setae broken), posterodistal lobe developed; merus, carpus, propodus, and dactylus in length ratio of 1.0: 1.0: 1.0: 0.2, 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. 10 D): coxa bilobed, anterior margin of anterior lobe with cluster of setae, posterior margin of posterior lobe with 2 setae; articles longer than those of pereopod 5; basis with 6 robust setae accompanied by short setae on anterior margin, 13 short setae on posterior margin (2 of them broken); merus, carpus, propodus, and dactylus in length ratio of 1.0: 1.0: 1.0: 0.2, 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. 10 E): coxa semicircular, anterior margin with cluster of setae, ventral to posterior margin with 3 setae; basis with pair of setae and 5 robust setae on anteroproximal submargin, 15 short setae on posterior margin; 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. 11 J): peduncle with 1 basofacial robust seta, 2 lateral and 4 medial robust setae marginally; outer ramus length 0.7 × peduncle, lateral and medial margins with 3 and 2 robust setae, respectively; inner ramus as long as outer ramus, medial margin with 3 robust setae. Uropod 2 ( Fig. 11 K): peduncle with 2 lateral and 1 medial robust setae marginally; outer ramus length 0.8 × peduncle, lateral margin with 2 robust setae; inner ramus length 1.1 × outer ramus, medial margin with 3 robust setae. Uropod 3 ( Fig. 11 L): peduncle length 1.8 × width, with robust and slender setae; inner ramus 1-articulate, length 1.5 × peduncle and 0.7× outer ramus, both margins with plumose setae; outer ramus 2-articulate, outer margin of article 1 with simple setae only, inner margin with plumose setae, article 2 short, length 0.05 × article 1.

Telson ( Fig. 11 M): length 1.2 × width, cleft for 84% of length; each lobe weakly rounded laterally, tapering distally, with several facial setae; apex truncate, with robust setae and slender setae longer than robust seta.

Description of female (NSMT-Cr 22730). Antenna 1 ( Fig. 11 N): peduncular articles 1–3 with length ratio of 1.0: 0.8: 0.5; peduncular article 2 length 2.6 × width. Antenna 2 ( Fig. 11 O): peduncular article 4 as long as article 5, length 3.2 × width, posterior margin with 6 clusters of setae and 2 single setae; peduncular article 5 length 4.9 × width, posterior margin with 4 clusters of setae and 4 single setae.

Gnathopod 1 ( Fig. 11 P): anterior margins of carpus and propodus with long setae, setae on anterodistal corner of carpus shorter than width of carpus; propodus not powerful, length 1.9 × width, anterior margin with 3 clusters of setae, palmar corner with 4 robust setae; dactylus short, not exceeding half of propodus. Gnathopod 2 ( Fig. 11 Q): setae on anterodistal corner of carpus slightly longer than width of carpus; propodus length 2.4 × width, anterior margin with 5 clusters of setae and single seta, palmar corner with 2 robust setae.

Oostegites on gnathopod 2 and pereopods 3–5.

Uropod 3 ( Fig. 11 R): peduncle length 1.8 × width; inner ramus length 1.2 × peduncle and 0.7 × outer ramus; article 2 of outer ramus length 0.07 × article 1.

Variation. Maxilla 1 bears 15–16 plumose setae on the medial margin of the inner plate. Maxilla 2 bears 11–12 facial setae of the inner plate.

Distribution. The species is distributed in western Honshu, Shikoku, Kyushu, and Dogo Island (Oki Islands, Shimane Prefecture), Japan ( Uéno 1940, 1941; Hiroki 1988; this study).

Remarks. This species was described by Uéno (1940) based on the specimens collected from Kiyotaki, Kyoto Prefecture, Japan. Unfortunately, the type materials of G. nipponensis were probably lost (Dr. Hiroshi Morino personal communication). Therefore, we examined the specimens collected from the type locality. The present specimens well agree with the original description of G. nipponensis except the character states of uropod 3. Uéno (1940) described plumose setae on the outer margin of the outer ramus of uropod 3 in the original description of G. nipponensis . However, we observed specimens from Kiyotaki, and confirmed that this species lacks plumose setae on the outer margin of the outer ramus of uropod 3, suggesting Uéno’s (1940) miss illustration in the original description.

Figures

FIGURE 9. Gammarus nipponensis Uéno, 1940, male (11.2 mm), NSMT-Cr 22729, Kiyotaki, Kyoto, Kyoto Prefecture, Japan. A, peduncular articles 1 – 3, accessory flagellum, and flagellar articles 1 – 3 of antenna 1, medial view; B, peduncular articles 1 – 5 and flagellar articles 1 – 2 of antenna 2, medial view; C, upper lip, anterior view; D, lower lip, ventral view; E, left mandible, medial view; F, incisor and lacinia mobilis of left mandible, medial view; G, incisor and lacinia mobilis of right mandible, lateral view; H, maxilla 1, dorsal view; I, outer plate of maxilla 1, dorsal view; J, maxilla 2, dorsal view; K, maxilliped, dorsal view; L, gnathopod 1, medial view; M, posterior margin of propodus and dactylus of gnathopod 1, medial view; N, gnathopod 2, medial view; O, palmar margin of propodus and dactylus of gnathopod 2, medial view.

FIGURE 10. Gammarus nipponensis Uéno, 1940, male (11.2 mm), NSMT-Cr 22729, Kiyotaki, Kyoto, Kyoto Prefecture, Japan. A – E, pereopods 3 – 7, respectively, medial views.

FIGURE 11. Gammarus nipponensis Uéno, 1940. A – M, male (11.2 mm), NSMT-Cr 22729, Kiyotaki, Kyoto, Kyoto Prefecture, Japan; N – R, female (9.1 mm), NSMT-Cr 22730, same locality. A – C, epimeral plates 1 – 3, respectively, lateral views; D – F, pleonites 1 – 3, respectively, dorsal views; G – I, urosomites 1 – 3, respectively, dorsal views; J and K, uropods 1 and 2, respectively, dorsal views; L, uropod 3, ventral view; M, telson, dorsal view; N, peduncular articles 1 – 3, accessory flagellum, and flagellar articles 1 – 3 of antenna 1, lateral view; O, peduncular articles 1 – 5 and flagellar articles 1 – 2 of antenna 2, medial view; P, carpus, propodus, and dactylus of gnathopod 1, medial view; Q, carpus, propodus, and dactylus of gnathopod 2, medial view; R, uropod 3, dorsal view.