Gammarus koreanus Uéno, 1940

Tomikawa, Ko, Tashiro, Satoko & Kobayashi, Norio, 2012, First Record of Gammarus koreanus (Crustacea, Amphipoda, Gammaroidea) from Japan, Based on Morphology and 28 S rRNA Gene Sequences, Species Diversity 17 (1), pp. 39-48 : 42-46

Gammarus koreanus Uéno, 1940

[New Japanese name: Chôsen-yokoebi] (Figs 2–4)

Gammarus (Rivulogammarus) pulex koreanus Uéno, 1940: 78–81 , gs 74–90; Lee and Kim 1980: 44; Barnard and Barnard 1983: 468.

Gammarus koreanus: Karaman 1984: 142 ; Karaman 1991: 48–54, gs VI 6, 7, VII–XI; Hou et al. 2007: 598.

Material examined. F ukue Island: NSMT-Cr 21670– 21673, 3 males (10.4–11.6 mm) and 1 female (8.0 mm), Arakawa River , 32°39′50̎N, 128°42′3̎E, Tamanouracho , Gotô city, Nagasaki Prefecture, 25 January 2010, coll . K . Tomikawa and S . Tashiro; NSMT-Cr 21975, 1 male (8.9 mm), Nanatakejinja , 32°40′58̎N, 128°41′23̎E, Tamanouracho , Gotô city, Nagasaki Prefecture, 25 January 2010, coll . K . Tomikawa and S . Tashiro; NSMT-Cr 21974, 1 male (9.5 mm), Dondonbuchidaki waterfall, 32°44′37̎N, 128°47′7̎E, Gotô city, Nagasaki Prefecture, 25 January 2010, coll . K . Tomikawa and S . Tashiro . Nakadôri Island : NSMT-Cr 21674–21677, 4 males (9.5–11.9 mm), Tsuridô River , 32°59′44̎N, 129°4′12̎E, Shin-kamigotôcho, Nagasaki Prefecture, 23 January 2010, coll . K . Tomikawa and S . Tashiro; NSMT-Cr 21678–21679, 2 males (7.8–10.0 mm), Aiko River , 32°57′40̎N, 129°4′44̎E, Shin-kamigotôcho, Nagasaki Prefecture, 23 January 2010, coll . K . Tomikawa and S . Tashiro; NSMT-Cr 21973, 4 males (8.3–11.7 mm), Ômizu , 33°4′24̎N, 129°5′58̎E, Shin-kamigotôcho, Nagasaki Prefecture, 23 January 2010, coll . K . Tomikawa and S . Tashiro.

Description. M ale. Head (Fig. 2A) slightly shorter than pereonites 1 and 2 combined, rostrum short, ventral margin of lateral cephalic lobe straight, antennal sinus rounded. Dorsal margins of pleonites 1–3 each with 4 setae. Epimeral plates 1–3 with 1, 1, and 2 robust setae on each ventral margin, and 3 short setae on each posterior margin; posteroventral corner of plates 2 and 3 pointed (Fig. 2A). Urosomites 1–3 with 4, 4, and 2 robust setae on dorsal margin, respectively.

Antenna 1 (Fig. 2A) longer than half of body length; each article of primary agellum with aesthetasc, calceoli absent. Antenna 2 (Fig. 2B, C) shorter than antenna 1; posterior margins of peduncular articles 4 and 5 with 2 and 3 clusters of short setae, respectively, except in specimens from Tsuridô River, Nakadôri Island, these with 3 and 4 clusters of long setae, respectively (Fig. 2C); agellum longer than half of peduncle length, calceoli absent.

Upper lip (Fig. 2E) with ne setae on rounded ventral margin. Lower lip (Fig. 2F) with broad outer lobes, inner lobes indistinct. Mandibles (Fig. 2G, H) with le and right incisors 5- and 4-dentate, respectively; le lacinia mobilis 4-dentate, right one bi d, bearing many teeth; each accessory setal row consisting of weakly pectinate setae; palp 3-articulate, article 3 with A, B, D, and E-setae. Maxilla 1 (Fig. 3A) with many plumose setae on medial margin of inner plate, inner surface setulose; outer plate subrectangular, with 11 serrate apical teeth, inner face setulose; palp 2-articulate, exceeding tip of outer plate, article 1 short, without marginal setae, article 2 with 8 robust and 3 slender apical setae. Maxilla 2 (Fig. 3B) with row of setae on medial margin of inner plate, oblique setal row of inner plate consisting of plumose setae. Maxilliped (Fig. 3C) with both apical and medial setae, including some robust and some plumose setae on outer plate; palp 4-articulate, article 2 with marginal and submarginal rows of setae, article 3 with facial setae on inner surface.

Gnathopod 1 (Fig. 3D,E) with setae on anterior and posterior margins of basis; palmar margin of propodus (Fig. 3E) weakly concave, with 15 robust setae; dactylus curved inward. Gnathopod 2 (Fig. 3F, G) also with setae on anterior and posterior margins of basis; anterior margin of propodus with apically curled long setae; palmar margin of propodus (Fig. 3G) weakly concave, with 6 robust setae; dactylus curved inward. Posterior margin of meri of pereopods 3 and 4 with apically curled long setae (Fig. 4C, D). Anterior margins of meri and carpi of pereopods 5–7 with robust and short setae. Lower margin of coxa 4 (Fig. 4D) straight, with posterior concavity; coxae 5 and 6 bilobed. Coxal gills pres- ent on gnathopod 2 and pereopods 3–7; accessory lobe absent.

Pleopods 1–3 each with retinacula, inner basal margin of inner ramus with bi d plumose setae. Uropod 1 with robust basofacial seta on peduncle; outer ramus shorter than peduncle, with 2–3 and 0–2 robust setae on outer and inner margins, respectively; inner ramus as long as outer, with 0–1 outer and 2–3 inner marginal robust setae, respectively. Uropod 2 with outer ramus shorter than peduncle, bearing 2–3 and 0–1 robust setae on outer and inner margins, respectively; inner ramus longer than outer, with 1–2 and 2–3 robust setae on outer and inner margins, respectively. Uropod 3 (Fig. 4G) with 2-articulate outer ramus, inner margin with plumose setae; inner ramus 49–63% as long as outer ramus, both outer and inner rami with plumose setae. Telson (Fig. 4I) slightly longer than wide, cle for 72–85% of length.

Female. Antennae 2 (Fig. 2D) with 2 clusters of setae each on posterior margin of peduncular articles 4 and 5. Propodus of gnathopods 1 and 2 (Fig. 4A, B) more slender than in male. Posterior margins of meri of pereopods 3 and 4 each with long, straight setae (Fig. 4E, F). Inner ramus of uropod 3 about half as long as of outer ramus (Fig. 4H).

Distribution.P reviously known from the northern part of the Korean Peninsula ( Uéno 1940); Ji’an, Jilin, in China ( Hou et al. 2007); and the Primorye region of Far-East Russia ( Karaman 1991). In Japan, this species is known only from Fukue Island and Nakadôri Islands, the Gotô Islands, Nagasaki Prefecture (this study).

Habitat.M ountain streams.

Molecular phylogenetic analysis.A total of 621–709 bp of 28S partial nuclear gene sequences was obtained from 10 individuals representing ve localities for G. koreanus from Japan. Excluding gap sites, the mutually alignable segments of the 28S rRNA sequences of 10 specimens representing G. koreanus from Japan, one representing G. koreanus from China, one representing G. nipponensis from Japan, and six specimens representing four species of Gammarus from China, i.e., 18 sequences in all, was 563 bp in length, with 157 variable sites and 93 parsimony-informative sites. Nucleotide frequencies among all samples were biased, with 43.2% A+T (mean: A = 22.4%, C = 26.4%, G = 30.4%, T= 20.8%). ffie average ratio of transitions (Ti) to transversions (Tv) was 1.14: 1. Maximum parsimony analysis recovered eight most parsimonious trees. Tree length was 358 steps, the consistency index (CI) was 0.833, and the retension index (RI) was 0.894.

Since the NJ, MP, and ML trees showed similar topology (the placements of G. nipponensis , G. electrus , G. nekkensis , Gammarus sp. 3 ZH-2007, and Gammarus sp. 4 ZH-2007 di ered slightly depending on the analysis), the NJ tree is shown here as a representative of all the trees (Fig. 5). ffie monophyly of Gammarus koreanus in China and Japan is supported by moderate bootstrap values in all trees (NJ = 88%, MP = 69%, and ML = 60%). Japanese G. koreanus forms a monophyletic group with moderate bootstrap values in all trees (NJ = 90%, MP = 81%, and ML = 61%). ffie genetic divergences between Japanese and Chinese G. koreanus are 3.4–4.9% of the uncorrected pairwise distances (p -distance) ( Table 2). Japanese specimens of G. koreanus collected from Nakadôri Island (GK3 to GK6) and Fukue Island (GK1 and GK2) are not all reciprocally monophyletic. ffie sequence divergences among haplotypes of Japanese G. koreanus are 0.2–3.5% of the p -distances ( Table 2).