Two new species of Jesogammarus from Japan (Crustacea, Amphipoda, Anisogammaridae), with comments on the validity of the subgenera Jesogammarus and Annanogammarus

Ko Tomikawa; Takafumi Nakano; Naoto Hanzawa

doi:10.3897/zse.93.12125

Abstract

Two new species of anisogammaris amphipod, Jesogammarus (Jesogammarus) bousfieldi and J. (J.) uchiyamaryui, are described from mountain streams in Yamagata Prefecture and from brackish waters on Iki and Fukue Islands, Nagasaki Prefecture, Japan. Jesogammarus bousfieldi is morphologically almost similar to J. paucisetulosus Morino, 1984. However, J. bousfieldi is distinguished from J. paucisetulosus by the more number of marginal setae on the pleonites. Jesogammarus uchiyamaryui resembles J. ikiensis Tomikawa, 2015, but the former differs from the latter by two setae on the posterior margin of peduncular article 2 of antenna 1, short and straight accessory lobes of coxal gills on gnathopod 2 and pereopods 3–5, densely setose ventral margins of coxae of female gnathopods 1 and 2 and pereopod 3, and a shorter inner ramus of uropod 3. Phylogenetic analyses using nuclear 28S rRNA, mitochondrial cytochrome c oxidase subunit I, and the 16S rRNA markers showed the sister relationship between J. bousfieldi and J. paucisetulosus. However, the phylogenetic position of J. uchiyamaryui remains uncertain. Both new species were genetically highly diverged comparable to intraspecific divergence among other Jesogammarus species. The species diversity related to habitat and the subgeneric classification of Jesogammarus are briefly discussed.

Key Words

Gammaroidea , Jesogammarus , Annanogammarus , molecular phylogeny, cryptic species

Introduction

The amphipod genus Jesogammarus Bousfield, 1979 inhabits fresh and brackish waters of the Japanese archipelago, the Korean Peninsula, and the Chinese continent (Bousfield 1979, Morino 1984, 1985, 1986, 1993, Lee and Seo 1990, 1992, Tomikawa and Morino 2003, Tomikawa et al. 2003, Hou and Li 2004, 2005, Tomikawa 2015). Jesogammarus was erected by Bousfield (1979) as a monotypic genus with the type species Anisogammarus jesoensis Schellenberg, 1937. In the same article, Bousfield established monotypic Annanogammarus Bousfield, 1979, of which the type species was designated Gammarus annandalei Tattersall, 1922.

Morino (1984) described a second species in Jesogammarus, J. paucisetulosus Morino, 1984 from Japan. Subsequently, Morino (1985) relegated Annanogammarus as a subgenus under Jesogammarus because the character combination of J. paucisetulosus and additional new species bridged the morphological gap between the two genera Jesogammarus and Annanogammarus. Morino concluded that Annanogammarus could be a distinct subgenus due to unequal coxal gill accessory lobes on gnathopod 2–pereopod 5 in length and simple robust setae on the palmar margin of female gnathopod 2. Molecular phylogenetic analyses of Jesogammarus recovered the monophyly of the subgenera Jesogammarus and Annanogammarus, respectively (Tomikawa et al. 2007, Tomikawa 2015).

The latest taxonomic study of the genus shows that Jesogammarus contains 18 species (Tomikawa 2015). The subgenus Annanogammarus consists of six freshwater species, and the subgenus Jesogammarus comprises 11 freshwater and one brackish-water species.

Two additional Jesogammarus species were collected during field surveys of fresh and brackish waters in Japan: one from mountain streams in Yamagata Prefecture and the other from brackish waters of Iki and Fukue Islands, Nagasaki Prefecture, Japan. A close examination of the external morphology revealed that these two species are distinct from their congeners and are described here as new species. In addition, the phylogenetic positions of these new species within Jesogammarus were estimated using nuclear 28S rRNA, the mitochondrial cytochrome c oxidase subunit I, and 16S rRNA sequences. A key to Jesogammarus species is provided and modified from that given in Tomikawa (2015).

Material and methods

Samples

Specimens of Jesogammarus were collected from three localities in Yamagata Prefecture and from two localities in Nagasaki Prefecture, Japan (Fig. 1). The specimens were collected by scooping with a fine-mesh hand-net and fixed in 99% ethanol on-site.

Figure 1.

Map showing the collection localities of the specimens examined in this study. The closed squares indicate the localities of J. bousfieldi sp. n. The closed diamonds denote the localities of J. uchiyamaryui sp. n. The closed circles indicate the localities of the referred materials used for the phylogenetic analyses. The symbols in red denote the type locality of each of the new species. Names of localities are shown in Table 1.

Morphological observation

All appendages of the examined specimens of the undescribed species were dissected in 70% ethanol and mounted in gum-chloral medium on glass slides under a stereomicroscope (Olympus SZX7). Specimens were examined using a light microscope (Nikon Eclipse Ni) and illustrated with the aid of a camera lucida. The body length from the tip of the rostrum to the base of the telson was measured along the dorsal curvature to the nearest 0.1 mm. The nomenclature of the setal patterns on the mandibular palp follows Stock (1974). The specimens are deposited in the Tsukuba Collection Center of the National Museum of Nature and Science, Tokyo (NSMT) and the Zoological Collection of Kyoto University (KUZ).

PCR and DNA sequencing

The extraction of genomic DNA from appendage muscles of the Jesogammarus materials preserved in 99% ethanol followed Tomikawa et al. (2014). Primer sets for the PCR and cycle sequencing reactions used in this study were as follows: for 28S rRNA (28S), 28SF and 28SR (Tomikawa et al. 2012); for cytochrome c oxidase subunit I (COI), Am-COI-H and Am-COI-T (Tomikawa 2015); for 16S rRNA (16S), 16STf (Macdonald III et al. 2005) and 16Sbr (Palumbi 1996; modified to correspond with “Fruit Fly”). The PCR reactions and DNA sequencing were performed using the identical method mentioned in Tomikawa (2015). In total, 59 sequences from the unidentified Jesogammarus specimens and J. paucisetulosus were newly obtained in this study, and deposited with the International Nucleotide Sequence Database Collaboration (INSDC) through the DNA Data Bank of Japan (Table 1).

Table 1.

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Samples used for the phylogenetic analyses. The information on the vouchers or isolate numbers is accompanied by the collection localities and the INSDC accession numbers. Sequences marked with an asterisk were obtained for the first time in the present study.

#	Species	Voucher or isolate #	Locality	INSDC #
#	Species	Voucher or isolate #	Locality	28S	COI	16S
Newly described Jesogammarus species in this study
6	J. bousfieldi sp. n.	KUZ Z1797	Gassan, Tsuruoka, Yamagata Prefecture, Japan	LC214776*	LC214536*	LC214793*
6	J. bousfieldi sp. n.	KUZ Z1798	Gassan, Tsuruoka, Yamagata Prefecture, Japan	LC214777*	LC214537*	LC214794*
5	J. bousfieldi sp. n.	KUZ Z1799	Aburato, Tsuruoka, Yamagata Prefecture, Japan	LC214778*	LC214538*	LC214795*
5	J. bousfieldi sp. n.	KUZ Z1800	Aburato, Tsuruoka, Yamagata Prefecture, Japan	LC214779*	LC214539*	LC214796*
3	J. bousfieldi sp. n.	KUZ Z1801	Mamurogawa, Yamagata Prefecture, Japan	LC214782*	LC214541*	LC214798*
3	J. bousfieldi sp. n.	KUZ Z1802	Mamurogawa, Yamagata Prefecture, Japan	LC214783*	LC214542*	LC214799*
18	J. uchiyamaryui sp. n.	KUZ Z1803	Tanie River, Iki, Nagasaki Prefecture, Japan	LC214773*	LC214533*	LC214790*
18	J. uchiyamaryui sp. n.	KUZ Z1804	Tanie River, Iki, Nagasaki Prefecture, Japan	LC214774*	LC214534*	LC214791*
20	J. uchiyamaryui sp. n.	KUZ Z1805	Mukata, Goto, Nagasaki Prefecture, Japan	LC214788*	LC214545*	LC214802*
20	J. uchiyamaryui sp. n.	KUZ Z1806	Mukata, Goto, Nagasaki Prefecture, Japan	LC214789*	LC214546*	LC214803*
Jesogammarus (Annanogammarus)
17	J. annandalei	G1162	Lake Biwa, Shiga Prefecture, Japan	LC214786*	LC052248	LC052269
	J. debilis	IZCAS-I-A0325	Fangshan, Beijing, China	EF582997		EF582846
15	J. fluvialis	G83	Samegai, Shiga Prefecture, Japan	LC214766*	LC052236	LC052257
16	J. naritai	G1167	Lake Biwa, Shiga Prefecture, Japan	LC214787*	LC052249	LC052270
13	J. suwaensis	G88	Lake Suwa, Nagano Prefecture, Japan	LC214767*	LC052237	LC052258
13	J. suwaensis	G89	Lake Suwa, Nagano Prefecture, Japan	LC214768*	LC052238	LC052259
Jesogammarus (Jesogammarus)
7	J. fujinoi	G17	Gobanmiki, Yamagata, Yamagata Prefecture, Japan	LC214762*	LC052232	LC052253
	J. hebeiensis	IZCAS-I-A0294	Yanqing, Beijing, China	EF582998		EF582847
10	J. hinumensis	G52	Lake Hinuma, Ibaraki Prefecture, Japan	LC214765*	LC052235	LC052256
14	J. hokurikuensis	G383	Takinami, Fukui, Fukui Prefecture, Japan	LC214771*	LC052241	LC052262
19	J. ikiensis	G515	Katsumoto, Iki, Nagasaki Prefecture, Japan	LC214772*	LC052242	LC052263
1	J. jesoensis	G164	Sapporo, Hokkaido, Japan	LC214769*	LC052239	LC052260
2	J. mikadoi	G13	Rokugo, Akita Prefecture, Japan	LC214761*	LC052231	LC052252
9	J. paucistulosus	G1037	Mito, Ibaraki Prefecture, Japan	LC214780*	LC052247	LC052268
9	J. paucistulosus	G1038	Mito, Ibaraki Prefecture, Japan	LC214781*	LC214540*	LC214797*
11	J. paucistulosus	G1017	Sakuragawa, Ibaraki Prefecture, Japan	LC214775*	LC214535*	LC214792*
8	J. paucistulosus	G1159	Kitaibaraki, Ibaraki Prefecture, Japan	LC214784*	LC214543*	LC214800*
8	J. paucistulosus	G1160	Kitaibaraki, Ibaraki Prefecture, Japan	LC214785*	LC214544*	LC214801*
4	J. shonaiensis	G192	Sakata, Yamagata Prefecture, Japan	LC214770*	LC052240	LC052261
12	J. spinopalpus	G32	Onjuku, Chiba Prefecture, Japan	LC214763*	LC052233	LC052254
Outgroup
	Eogammarus kygi	G1	Naibetsu River, Eniwa, Hokkaido, Japan	LC214759*	LC052229	LC052250
	Eogammarus possjeticus	G3	Akkeshi, Hokkaido, Japan	LC214760*	LC052230	LC052251
	Spasskogammarus spasskii	G35	Akkeshi, Hokkaido, Japan	LC214764*	LC052234	LC052255

Molecular phylogenetic analyses

Thirty-two published sequences were obtained from the INSDC for use in molecular phylogenetic analyses (Table 1). Along with the two Chinese Jesogammarus species, J. (A.) debilis Hou & Li, 2005 and J. (J.) hebeiensis Hou & Li, 2004, used in the previous phylogenetic study (Hou et al. 2007), three anisogammarid species, Eogammarus kygi (Derzhavin, 1923), E. possjeticus (Tzvetkova, 1967), and Spasskogammarus spasskii (Bulycheva, 1952), were included in the analyses as outgroup taxa.

The phylogenetic positions of the unidentified species among Jesogammarus were estimated based on the gene fragments of 28S, COI, and 16S sequences. The alignment of COI was trivial, as no indels were observed. The 28S and 16S sequences were aligned using MAFFT v. 7.305b L-INS-i (Katoh and Standley 2013). The lengths of 28S, COI and 16S sequences were 717, 362, and 420 bp, respectively. The concatenated sequences thus yielded 1,499 bp of alignment positions. One of each four completely identical sequence pairs (KUZ Z1803 and KUZ Z1804; KUZ Z1799 and KUZ Z1800; G1037 and G1038; and KUZ Z1805 and KUZ Z1806) was removed from the dataset using the “pgelimdupseq” command implemented in Phylogears v. 2.0.2014.03.08 (Tanabe 2008).

Phylogenetic relationships were estimated using maximum likelihood (ML) and Bayesian inference (BI). ML phylogenies were conducted using RAxML v. 8.2.8 (Stamatakis 2014) with GTRCAT, immediately after nonparametric bootstrapping (Felsenstein 1985) (BS) conducted with 1,000 replicates. The best-fit partitioning scheme for the ML analysis was identified with the Akaike information criterion (Akaike 1974) using PartitionFinder v. 1.1.1 (Lanfear et al. 2012) with the “all” algorithm: each of 28S, 1st to 3rd positions of COI and 16S were, respectively, treated as a separate partition.

BI and Bayesian posterior probabilities (PPs) were estimated using MrBayes v. 3.2.6 (Ronquist et al. 2012). The best-fit models for each partition were identified with the Bayesian information criterion (Schwarz 1978) using PartitionFinder with the “all” algorithm: for 28S and the 2nd position of COI, K80+G; for 1st position of COI, SYM+I; for the 3rd position of COI, GTR+G; and for 16S, HKY+G. Two independent runs of four Markov chains were conducted for 5 million generations, and the tree was sampled every 100 generations. The parameter estimates and convergence were checked using Tracer v. 1.6.0 (Rambaut and Drummond 2013) and the first 20,001 trees were discarded based on the results.

Taxonomy

Jesogammarus (Jesogammarus) bousfieldisp. n.

http://zoobank.org/EC1F1C3D-259C-4D7A-B88D-51AA229605A2

New Japanese name: Nagare-yokoebi

Figs 2, 3, 4, 5, 6, 7, 8

Type materials

Holotype: Male (9.8 mm), NSMT-Cr 25470, Aburato (38°45′23.9″N, 139°43′14.7″E), Tsuruoka, Yamagata Prefecture, Japan, 26 November 2013, collected by K. Tomikawa. Paratypes: 1 ovigerous female (6.6 mm), NSMT-Cr 25471, 1 male (8.2 mm), KUZ Z1799, 1 male (8.4 mm), KUZ Z1800, data same as for holotype; 1 female (8.9 mm), KUZ Z1797, 1 male (9.0 mm), KUZ Z1798, Gassan (38°33′53.2″N, 139°56′24.3″E), Tsuruoka, Yamagata Prefecture, Japan, 26 November 2013, collected by K. Tomikawa; 1 Male (10.4 mm), NSMT-Cr 25472, 1 ovigerous female (9.2 mm), NSMT-Cr 25473, 1 ovigerous female (7.8 mm), KUZ Z1801, 1 male (10.3 mm), KUZ Z1802, Otaki, Mamurogawa, Yamagata Prefecture, Japan, 15 April 2001, collected by K. Tomikawa.

Type locality

Japan, Yamagata Prefecture: Tsuruoka, Aburato.

Description

Male [NSMT-Cr 25470, 9.8 mm]. Head (Fig. 2) with short rostrum; ventral margin of lateral cephalic lobe weakly concave; antennal sinus rounded; eyes oval, major axis 0.2 × height of head. Dorsal surfaces of pereonites smooth (Fig. 2). Dorsal margins of pleonites 1–3 (Fig. 3A–C) with 4, 4, and 9 setae, respectively. Posterior margin of epimeral plate 1 rounded with seta, posteroventral corner with seta, anteroventral corner with 8 setae (Fig. 3D); posterior margin of plate 2 almost straight with 4 setae, posteroventral corner quadrate with seta, anteroventral corner with 4 setae, ventral submargin with 2 robust setae and 2 small setae (Fig. 3E); posterior margin of plate 3 almost straight with 5 setae, posteroventral corner quadrate with seta, anteroventral corner with 2 setae, ventral submargin with 2 robust setae (Fig. 3F). Urosomites 1–3 (Fig. 3G–I) with 8, 6, and 2 robust setae associated with slender setae on dorsal margins.

Figure 2.

Jesogammarus bousfieldi sp. n., holotype, male (9.8 mm), NSMT-Cr 25470. Habitus, lateral view.

Antenna 1 (Fig. 3J): length 0.5 × body length; peduncular articles 1–3 in length ratio of 1.0 : 0.8 : 0.5; posterodistal corner of peduncular article 1 without robust seta, posterior margin of peduncular article 1 with 2 clusters and 1 pair of setae and 1 single seta, posterior margin of peduncular article 2 with 5 clusters and 1 pairs of setae, posterior margin of peduncular article 3 with 2 clusters and 1 pair of setae; accessory flagellum 6-articulate; primary flagellum 26-articulate, each article with 1 aesthetasc.

Antenna 2 (Fig. 3K): length 0.6 × antenna 1; posterior margin of peduncular article 4 with 5 clusters of setae, posterior margin of peduncular article 5 with 3 clusters and 1 pair of setae and 1 single seta; flagellum 13-articulate, calceoli present (Fig. 3L).

Figure 3.

Jesogammarus bousfieldi sp. n., holotype, male (9.8 mm), NSMT-Cr 25470. A–C dorsal margins of pleonites 1–3, respectively, dorsal views; D–F epimeral plates 1–3, respectively, lateral views; G–I dorsal margins of urosomites 1–3, respectively, dorsal views; J peduncular articles 1–3, accessory flagellum, and flagellar articles 1–3 of antenna 1, medial view; K peduncular articles 1–5 and flagellar articles 1–3 of antenna 2, medial view; L calceolus of antenna 2, medial view; M upper lip, anterior view; N left mandible, medial view; O incisor and lacinia mobilis of left mandible, lateral view; P incisor and lacinia mobilis of right mandible, lateral view; Q lower lip, ventral view.

Mouthparts. Upper lip (= labrum) (Fig. 3M) with rounded distal margin, bearing fine setae. Mandibles (Fig. 3N–P) with left and right incisors 5- and 4-dentate, respectively, left lacinia mobilis 4-dentate, right one bifid, bearing many teeth; molar process triturative, with plumose seta; accessory setal rows of left and right mandibles with 7 and 6 blade-like setae, respectively; palp 3-articulate with length ratio of 1.0 : 4.4 : 4.0, palp article 1 bare, article 2 with 22 setae, article 3 with 2 clusters and 1 pair of A-setae, 1 pair of B-setae, and many C-, D-, and E-setae. Lower lip (= labium) (Fig. 3Q) with broad outer lobes, inner lobes indistinct. Maxilla 1 (Fig. 4A) with inner and outer plates and palp; medial margin and apical submargin of inner plate with 20 and 2 plumose setae, respectively; outer plate subrectangular, with 11 serrate teeth apically (Fig. 4B); palp 2-articulate, longer than outer plate, article 1 lacking marginal setae, article 2 with 7 robust setae and 1 slender seta on its apical margin and 3 slender setae on its submargin, outer margin without setae. Maxilla 2 (Fig. 4C) with oblique inner row of 19 plumose setae on inner plate; outer plate almost as long as inner plate. Maxilliped (Fig. 4D) with inner and outer plates and palp; inner plate with 3 and 2 robust setae on apical and inner margins, respectively; outer plate with plumose setae on apical margin and robust setae on inner margin; palp 4-articulate, article 2 with inner marginal and submarginal rows of setae, article 3 with facial setae, article 4 slightly curved inward, with slender nail.

Figure 4.

Jesogammarus bousfieldi sp. n., holotype, male (9.8 mm), NSMT-Cr 25470. A maxilla 1, dorsal view; B outer plate of maxilla 1, dorsal view; C maxilla 2, dorsal view; D maxilliped, dorsal view; E gnathopod 1, lateral view; F palmar margin of propodus of gnathopod 1, lateral view; G gnathopod 2, lateral view; H palmar margin of propodus of gnathopod 2, lateral view; I pereopod 3, lateral view; J pereopod 4, lateral view.

Gnathopod 1 (= pereopod 1) (Fig. 4E): coxa (= article 1) with 13 setae on anterodistal to ventral margin; anterior and posterior margins of basis (= article 2) with long setae; carpus (= article 5) length 1.5 × width, anterior margin with 1 pair of setae; propodus (= article 6) length 1.4 × carpus and 1.4 × width, anterior margin with 1 pair and 1 cluster of setae, palmar margin oblique, weakly convex, with 15 peg-shaped robust setae (Fig. 4F); dactylus (= article 7) as long as palmar margin.

Gnathopod 2 (= pereopod 2) (Fig. 4G): coxa with 6 marginal setae on ventral margin, posterodistal corner with 1 seta; anterior and posterior margins of basis with long setae; carpus length 1.5 × width, anterior margin with 1 pair of setae; propodus length 1.2 × carpus and 1.5 × width, respectively, anterior margin with 2 clusters of setae, palmar margin oblique, weakly convex, with 10 peg-shaped robust setae (Fig. 4H); dactylus as long as palmar margin.

Pereopod 3 (Fig. 4I): coxa with 7 marginal setae on ventral part, posteroproximal part with 2 setae; anterior and posterior margins of basis with long setae, anterodistal corner of basis with robust seta.

Pereopod 4 (Fig. 4J): coxa expanded with posterior concavity, bearing 2 setae on anterodistal corner and 6 setae on ventral margin; anterior and posterior margins of basis with long setae, anterodistal corner with robust seta.

Pereopod 5 (Fig. 5A): coxa bilobed, anterior lobe with apical seta, ventral margin of posterior lobe with 3 setae, posterodistal corner rounded with seta; posterior margin of basis weakly expanded, with 13 setae; anterior and posterior margins of merus to propodus with robust and slender setae.

Figure 5.

Jesogammarus bousfieldi sp. n., holotype, male (9.8 mm), NSMT-Cr 25470 (A–C and E–P) and paratype, female (6.6 mm), NSMT-Cr 25471 (D). A coxa–ischium of pereopod 5, lateral view; B coxa–ischium of pereopod 6, lateral view; C coxa–ischium of pereopod 7, lateral view; D–I coxal gills on gnathopod 2 and pereopods 3–7, lateral views; J pleopod 1, lateral view, distal parts of rami omitted; K bifid plumose seta (clothes-pin seta) on inner basal margin of inner ramus of pleopod 1, lateral view; L retinacula on peduncle of pleopod 1, lateral view; M uropod 1, dorsal view; N uropod 2, dorsal view; O uropod 3, dorsal view; P telson, dorsal view.

Pereopod 6 (Fig. 5B): coxa bilobed, anterior lobe with anteroproximal setae, ventral margin of posterior lobe with 3 setae, posterodistal corner rounded with seta; posterior margin of basis weakly expanded with 12 setae, posterodistal corner with robust seta associated with small seta; anterior and posterior margins of merus to propodus with robust and slender setae.

Pereopod 7 (Fig. 5C): ventral margin of coxa weakly concave, bearing 2 setae on anterior part and 4 setae on posteroventral part; posterior margin of basis weakly expanded with 9 setae, posterodistal corner with robust seta associated with 2 small setae; anterior and posterior margins of merus to propodus with robust and slender setae.

Coxal gills on gnathopod 2 and pereopods 3–5 (Fig. 5D–G) with 2 accessory lobes, posterior lobes longer than anterior ones, gills on pereopods 6 and 7 (Fig. 5H, I) each with 1 accessory lobe.

Pleopods 1–3 (Fig. 5J) each with paired retinacula (Fig. 5L) on inner margin of peduncle, and bifid plumose setae (= clothes-pin setae) (Fig. 5K) on inner basal margin of inner ramus.

Uropods. Uropod 1 (Fig. 5M): peduncle with robust seta on basofacial part, inner and outer margins each with 2 robust setae, inner and outer distal corners with 1 and 2 robust setae, respectively; inner ramus length 0.7 × peduncle, inner margin with 2 robust setae and outer margin with robust seta; outer ramus length 0.8 × inner ramus, inner and outer margins each with robust seta. Uropod 2 (Fig. 5N): peduncle with 2 robust setae on inner and outer margins, respectively, inner and outer distal corners each with robust seta; inner ramus length 0.8 × peduncle, its inner and outer margins each with robust seta; outer ramus length 0.9 × inner ramus, marginally bare. Uropod 3 (Fig. 5O): peduncle length 0.3 × outer ramus; inner ramus length 0.2 × outer ramus, with 2 slender setae and robust seta on inner margin, and apical seta; outer ramus 2-articulate, inner and outer margins of article 1 each with 3 clusters of setae, some of which robust, inner margin with plumose seta, article 2 length 0.1 × article 1, with simple setae apically.

Telson (Fig. 5P) length 0.8 times × width, cleft for 79% of length; each lobe with 2 robust setae and slender setae.

Female [NSMT-Cr 25471, 6.6 mm]. Antenna 1 (Fig. 6A): peduncular articles 1–3 in length ratio of 1.0 : 0.7 : 0.5; posterior margin of peduncular article 1 with 3 pairs of setae and single seta, posterior margin of peduncular article 2 with 5 clusters of setae, posterior margin of peduncular article 3 with 2 clusters of setae; accessory flagellum 4-articulate; primary flagellum 19-articulate.

Figure 6.

Jesogammarus bousfieldi sp. n., paratype, female (6.6 mm), NSMT-Cr 25471. 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 1–3 of antenna 2, medial view; C gnathopod 1, lateral view; D palmar margin of propodus of gnathopod 1, lateral view; E gnathopod 2, lateral view; F palmar margin of propodus of gnathopod 2, lateral view; G brood plate of gnathopod 2, lateral view.

Antenna 2 (Fig. 6B): posterior margin of peduncular article 4 with 1 cluster and 4 pairs of setae and single seta, posterior margin of peduncular article 5 with 3 clusters and 2 pairs of setae; flagellum 12-articulate, calceoli absent.

Gnathopod 1 (Fig. 6C): posteroproximal part of coxa without setae; carpus length 1.4 × width; propodus slightly longer than merus and 1.5 × width; palmar margin (Fig. 6D) with 5 robust setae.

Gnathopod 2 (Fig. 6E): posteroproximal part of coxa without setae; carpus length 1.9 × width; propodus almost as long as merus, lenght 1.8 × width; palmar margin (Fig. 6F) with 3 robust and 4 pectinate robust setae.

Posterior margin of bases of pereopods 5–7 more expanded than in male (Fig. 7A–C).

Figure 7.

Jesogammarus bousfieldi sp. n., paratype, female (6.6 mm), NSMT-Cr 25471. A coxa–ischium of pereopod 5, lateral view; B coxa–ischium of pereopod 6, lateral view; C coxa–ischium of pereopod 7, lateral view; D uropod 3, dorsal view.

Brood plates (= oostegites) (Fig. 6G): broad, with numerous marginal setae.

Uropod 3 (Fig. 7D): peduncle length 0.4 × outer ramus; inner ramus length 0.3 × outer ramus; inner and outer margins of article 1 of outer ramus each with 2 clusters of setae, plumose setae absent, article 2 length 0.2 × article 1.

Egg number 6 (16 in female from Mamurogawa [NSMT-Cr 25473]).

Etymology

Jesogammarus bousfieldi was named in remembrance of the late Dr Edward Lloyd Bousfield, who enthusiastically guided and encouraged many Japanese amphipodologists, and sadly passed away on 7 September 2016.

Distribution and habitat

This species is known only from Yamagata Prefecture. The specimens were collected from small mountain streams. Ovigerous females were collected from November to April.

Figure 8.

Jesogammarus bousfieldi sp. n., not preserved, precopula pair (male: upper, female: lower). Photographed by Ryu Uchiyama.

Remarks

Jesogammarus bousfieldi resembles J. paucisetulosus closely in having 1) small eyes, 2) posterodistal corner of peduncular article 1 of antenna 1 without robust seta, 3) posterior margins of peduncular articles antennae 1 and 2 with many long setae, 4) outer margin of palp article 2 of maxilla 1 without setae, and 5) ventral margins of coxae of female gnathopods 1 and 2 with few setae. However, J. bousfieldi differs from J. paucisetulosus by the number of setae on the dorsal margins of pleonites 1–3: each pleonite with more than 4 setae in J. bousfieldi vs. 0–3 in J. paucisetulosus.

Jesogammarus (Jesogammarus) uchiyamaryuisp. n.

http://zoobank.org/7E6DE7E7-4892-4526-B42B-A2414895D665

New Japanese name: Uchiyama-yokoebi

Figs 9, 10, 11, 12, 13, 14

Type materials

Holotype: Male (10.3 mm), NSMT-Cr 25474, Tanie River (33°49′16.9″N, 129°44′0.4″E), Ashibe, Iki, Nagasaki Prefecture, Japan, 8 March 2012, collected by K. Tomikawa and S. Tashiro. Paratypes: 1 ovigerous female (9.2 mm), NSMT-Cr 25475, 1 male (12.1 mm), KUZ Z1803, 1 male (12.0 mm), KUZ Z1804, data same as for holotype; 1 male (8.6 mm), KUZ Z1805, 1 male (9.1 mm), KUZ Z1806, Mukata (32°42′54.7″N, 128°50′19.3″E), Goto, Nagasaki Prefecture, Japan, 15 December 2015, collected by K. Tomikawa and S. Tashiro.

Type locality

Japan, Nagasaki Prefecture: Iki, Ashibe, Tanie River.

Description

Male [NSMT-Cr 25474, 10.3 mm]. Head (Fig. 9) with short rostrum; ventral margin of lateral cephalic lobe weakly concave; antennal sinus rounded; eyes reniform, major axis 0.4 × height of head. Dorsal surfaces of pereonites smooth (Fig. 9). Dorsal margins of pleonites 1–3 (Fig. 10A–C) each with 2 setae. Posterior margin of epimeral plate 1 rounded with seta, posteroventral corner with seta, anteroventral to ventral margin with 7 setae (Fig. 10D); posterior margin of plate 2 weakly sinusoid with seta, posteroventral corner quadrate with seta, ventral margin and submargin with 3 and 2 robust setae, respectively (Fig. 10E); posterior margin of plate 3 slightly waved with seta, posteroventral corner weakly pointed with seta, anteroventral to ventral margin with 4 robust and 1 small setae (Fig. 10F). Urosomites 1–3 (Fig. 10G–I) with 10, 6, and 6 robust setae on dorsal margins.

Figure 9.

Jesogammarus uchiyamaryui sp. n., holotype, male (10.3 mm), NSMT-Cr 25474. Habitus, lateral view.

Antenna 1 (Fig. 10J): length 0.6 × body length; peduncular articles 1–3 in length ratio of 1.0 : 0.7 : 0.5; posterodistal corner of peduncular article 1 with robust seta, posterior margin of peduncular article 1 with single seta, posterior margin of peduncular article 2 with 1 cluster and 1 pair of setae, posterior margin of peduncular article 3 with pair of setae; accessory flagellum 5-articulate; primary flagellum 28-articulate, each article with 1 aesthetasc.

Antenna 2 (Fig. 10K): length 0.7 × antenna 1; posterior margin of peduncular article 4 with 2 clusters and 1 pair of setae, posterior margin of peduncular article 5 with 2 clusters of setae; flagellum 14-articulate, calceoli present (Fig. 10L).

Figure 10.

Jesogammarus uchiyamaryui sp. n., holotype, male (10.3 mm), NSMT-Cr 25474. A–C dorsal margins of pleonites 1–3, respectively, dorsal views; D–F epimeral plates 1–3, respectively, lateral views; G–I dorsal margins of urosomites 1–3, respectively, dorsal views; J peduncular articles 1–3, accessory flagellum, and flagellar articles 1–3 of antenna 1, medial view; K peduncular articles 1–5 and flagellar articles 1–3 of antenna 2, medial view; L calceolus of antenna 2, medial view; M upper lip, anterior view; N left mandible, medial view; O incisor and lacinia mobilis of left mandible, lateral view; P incisor and lacinia mobilis of right mandible, lateral view; Q lower lip, ventral view.

Mouthparts. Upper lip (= labrum) (Fig. 10M) with rounded distal margin, bearing fine setae. Mandibles (Fig. 10N–P) with left and right incisors 5- and 4-dentate, respectively, left lacinia mobilis 5-dentate, right one bifid, bearing many teeth; molar process triturative, with plumose seta; accessory setal rows of left and right mandibles each with 6 blade-like setae; palp 3-articulate with length ratio of 1.0 : 2.3 : 2.0, palp article 1 bare, article 2 with 16 setae, article 3 with 1 cluster and 2 pairs of A-setae, single B-seta, and many C-, D-, and E-setae. Lower lip (= labium) (Fig. 10Q) with broad outer lobes, inner lobes indistinct. Maxilla 1 (Fig. 11A) with inner and outer plates and palp; medial margin of inner plate with 16 plumose setae 2 plumose setae, apical submargin with 4 setae; outer plate subrectangular, with 11 serrate teeth apically (Fig. 11B); palp 2-articulate, longer than outer plate, article 1 lacking marginal setae, article 2 with 5 robust setae and 1 slender seta on its apical margin and 4 slender setae on its submargin, outer margin with 2 setae. Maxilla 2 (Fig. 11C) with oblique inner row of 16 plumose setae on inner plate; outer plate slightly longer than inner plate. Maxilliped (Fig. 11D) with inner and outer plates and palp; inner plate with 3 and 2 robust setae on apical and inner margins, respectively; outer plate with plumose setae on apical margin and robust setae on inner margin; palp 4-articulate, article 2 with inner marginal and submarginal rows of setae, article 3 with facial setae, article 4 slightly curved inward, with slender nail.

Gnathopod 1 (Fig. 11E): coxa with 12 setae on anterodistal to to posterodistal margin; anterior and posterior margins of basis with long setae; carpus length 1.5 × width, anterior margin with single seta; propodus length 1.3 × carpus and 1.4 × width, anterior margin with 2 clusters of setae and single seta, palmar margin oblique, weakly convex, with 15 peg-shaped robust setae (Fig. 11F); dactylus as long as palmar margin.

Figure 11.

Jesogammarus uchiyamaryui sp. n., holotype, male (10.3 mm), NSMT-Cr 25474. A maxilla 1, dorsal view; B outer plate of maxilla 1, dorsal view; C maxilla 2, dorsal view; D maxilliped, dorsal view; E gnathopod 1, lateral view; F palmar margin of propodus of gnathopod 1, lateral view; G gnathopod 2, lateral view; H palmar margin of propodus of gnathopod 2, lateral view; I pereopod 3, lateral view; J pereopod 4, lateral view.

Gnathopod 2 (Fig. 11G): coxa with 8 marginal setae on anterodistal to posterodistal margin, medial surface with 2 setae; anterior and posterior margins of basis with long setae; carpus length 1.7 × width, anterior margin with 1 pair of setae; propodus length 1.1 × carpus and 1.5 × width, respectively, anterior margin with 1 cluster and 1 pair of setae, palmar margin oblique, weakly convex, with 14 peg-shaped robust setae (Fig. 11H); dactylus as long as palmar margin.

Pereopod 3 (Fig. 11I): coxa with 4 and 2 marginal setae on anterodistal and posterodistal parts, respectively; anterior and posterior margins of basis with long setae, anterodistal corner of basis without robust seta.

Pereopod 4 (Fig. 11J): coxa expanded with posterior concavity, bearing 2 setae on anterodistal corner and 4 setae on ventral margin; anterior and posterior margins of basis with long setae, anterodistal corner with robust seta.

Pereopod 5 (Fig. 12A): coxa bilobed, anterior lobe with 2 apical setae, ventral margin of posterior lobe with 2 setae, posterodistal corner not pointed with seta; posterior margin of basis weakly expanded, with 9 setae; anterior and posterior margins of merus to propodus with robust and slender setae.

Figure 12.

Jesogammarus uchiyamaryui sp. n., holotype, male (10.3 mm), NSMT-Cr 25474. A coxa–ischium of pereopod 5, lateral view; B coxa–ischium of pereopod 6, lateral view; C coxa–ischium of pereopod 7, lateral view; D–I coxal gills on gnathopod 2 and pereopods 3–7, lateral views; J pleopod 1, lateral view, distal parts of rami omitted; K bifid plumose seta (clothes-pin seta) on inner basal margin of inner ramus of pleopod 1, lateral view; L retinacula on peduncle of pleopod 1, lateral view; M uropod 1, dorsal view; N uropod 2, dorsal view; O uropod 3, dorsal view; P telson, dorsal view.

Pereopod 6 (Fig. 12B): coxa bilobed, anterior lobe with apical seta, anterior margin with long setae, ventral margin of posterior lobe with 2 setae, posterodistal corner weakly pointed with seta; posterior margin of basis weakly expanded with 9 setae, posterodistal corner with robust seta; anterior and posterior margins of merus to propodus with robust and slender setae.

Pereopod 7 (Fig. 12C): ventral margin of coxa weakly concave, bearing 3 setae on anterior margin and 4 setae on posteroventral margin; posterior margin of basis weakly expanded with 7 setae, posterodistal corner with 2 robust setae; anterior and posterior margins of merus to propodus with robust and slender setae.

Coxal gills on gnathopod 2 and pereopods 3–5 (Fig. 12D–G) with 2 accessory lobes, both anterior and posterior lobes short, subequal, gills on pereopods 6 and 7 (Fig. 12H, I) each with 1 accessory lobe.

Pleopods 1–3 (Fig. 12J) each with paired retinacula (Fig. 12L) on inner margin of peduncle, and bifid plumose setae (= clothes-pin setae) (Fig. 12K) on inner basal margin of inner ramus.

Uropods. Uropod 1 (Fig. 12M): peduncle with robust seta on basofacial part, inner and outer margins with 4 and 2 setae, respectively, inner and outer distal corners with 1 and 2 robust setae, respectively; inner ramus length 0.7 × peduncle, inner margin with 2 robust setae and outer margin with 1 robust and 1 small setae; outer ramus length 0.9 × inner ramus, inner and outer margins each with robust seta. Uropod 2 (Fig. 12N): inner and outer margins of peduncle each with 2 setae, outer distal corner with robust seta; inner ramus length 0.7 × peduncle, its inner and outer margins each with robust seta; outer ramus length 0.9 × inner ramus, marginally bare. Uropod 3 (Fig. 12O): peduncle length 0.2 × outer ramus; inner ramus length 0.2 × outer ramus, with inner marginal seta and apical seta; outer ramus 2-articulate, inner and outer margins of article 1 each with 4 clusters of setae, some of which robust, both inner and outer margins with plumose setae, article 2 length 0.2 × article 1, with simple setae apically.

Telson (Fig. 12P) almost as long as wide, cleft for 63% of length; each lobe with 2 or 3 robust setae and slender setae.

Female [NSMT-Cr 25475, 9.2 mm]. Antenna 1 (Fig. 13A): peduncular articles 1–3 in length ratio of 1.0 : 0.7 : 0.4; posterior margin of peduncular article 1 with 2 single setae, posterior margin of peduncular article 2 with 2 pairs of setae, posterior margin of peduncular article 3 with cluster of setae; accessory flagellum 6-articulate; primary flagellum 31-articulate.

Figure 13.

Jesogammarus uchiyamaryui sp. n., paratype, female (9.2 mm), NSMT-Cr 25475. 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 1–3 of antenna 2, medial view; C gnathopod 1, lateral view; D palmar margin of propodus of gnathopod 1, lateral view; E gnathopod 2, lateral view; F palmar margin of propodus of gnathopod 2, lateral view; G brood plate of gnathopod 2, lateral view; H coxa–ischium of pereopod 5, lateral view; I coxa–ischium of pereopod 6, lateral view; J coxa–ischium of pereopod 7, lateral view; K uropod 3, dorsal view.

Antenna 2 (Fig. 13B): posterior margin of peduncular article 4 with 2 clusters of setae, posterior margin of peduncular article 5 with 2 pairs of setae and single seta; flagellum 13-articulate, calceoli absent.

Gnathopod 1 (Fig. 13C): posterior margin of coxa with many setae; carpus length 1.4 × width; propodus length 1.2 × merus and 1.6 × width, respectively; palmar margin (Fig. 13D) with 5 robust setae.

Gnathopod 2 (Fig. 13E): posteroproximal part of coxa with numerous setae; carpus length 2.2 × width; propodus length 0.9 × merus and 2.1 × width, respectively; palmar margin (Fig. 13F) with 1 robust and 10 pectinate robust setae.

Posterior margin of bases of pereopods 5–7 more expanded than in male (Fig. 13H–J).

Brood plates (Fig. 13G): broad, with numerous marginal setae.

Uropod 3 (Fig. 13K): peduncle length 0.3 × outer ramus; inner ramus length 0.2 × outer ramus; inner and outer margins of article 1 of outer ramus with 5 and 3 clusters/pairs of setae, article 2 length 0.2 × article 1.

Egg number 154.

Etymology

The specific name honors Mr Ryu Uchiyama (nature photographer), who provided many photos of living amphipods throughout KT’s amphipodological study.

Distribution and habitat

This species is known from Iki and Fukue Islands, Nagasaki Prefecture. The specimens were collected from river mouths subject to tidal action. An ovigerous female was collected in March.

Remarks

Jesogammarus uchiyamaryui is morphologically similar to J. ikiensis Tomikawa, 2015 in having 1) dorsal margin of pereonites 5–7 without setae, 2) a few (<4) setae on dorsal margin of pleonites 1–3, 3) large eyes, robust seta on posterodistal corner of peduncular article 1 of antenna 1, and 4) mandibular palp article 1 without robust setae. However, J. uchiyamaryui differs from J. ikiensis by the following features (features of J. ikiensis in parentheses): 1) posterior margin of peduncular article 2 of antenna 1 with two (three or four) setae, 2) accessory lobes of coxal gills on gnathopod 2 and pereopods 3–5 short and straight (long and curved), 3) ventral margins of coxae of female gnathopods 1 and 2 and pereopod 3 with numerous long setae (a few short setae), and 4) inner ramus of uropod 3 shorter than 0.2 (0.2–0.3) times as long as outer ramus. Jesogammarus uchiyamaryui is also similar to J. spinopalpus Morino, 1985 in having 1) short accessory lobes of coxal gills on gnathopod 2 and pereopods 3–5 and 2) densely setose ventral margins of coxae of female gnathopods 1 and 2. However, the former differs from the latter by the following features (features of J. spinopalpus in parentheses): 1) eyes large (small), 2) dorsal margins of pleonites 1–3 each with two setae (numerous), 3) the mandibular palp article 1 without robust setae (present), 4) inner ramus of uropod 3 shorter than 0.2 times as long as outer ramus (longer than 0.3), and 5) posterior margin of bases of female pereopods 5–7 with short (long) setae.

Figure 14.

Jesogammarus uchiyamaryui sp. n., not preserved, precopula pair (male: upper, female: lower). Photographed by Ryu Uchiyama.

Molecular phylogenies

The BI tree (mean ln L = −8918.44; Fig. 15) had an almost identical topology to that of the ML tree (ln L = −9156.46; not shown). The monophyly of the genus Jesogammarus was well-supported (BS = 100%, PP = 1.0). The genus Jesogammarus consisted of three monophyletic lineages: J. uchiyamaryui lineage (BS = 100%, PP = 1.0), the subgenus Annanogammarus lineage (BS = 100%, PP = 1.0), and the subgenus Jesogammarus lineage (BS = 99%, PP = 1.0). However, our phylogenetic analyses failed to resolve precise the phylogenetic relationships among these three lineages.

Figure 15.

Bayesian inference tree for 1,499 bp of nuclear 28S rRNA and mitochondrial COI and 16S rRNA markers. Numbers on nodes represent bootstrap values for maximum likelihood and Bayesian posterior probabilities.

The monophyly of the four species within the Annanogammarus lineage inhabiting Japan was well supported (BS = 94%, PP = 1.0). The Jesogammarus lineage comprised four subclades; however, the detailed phylogenetic relationships among these four lineages remain unresolved. The first subclade (BS = 100%, PP = 1.0) contains the Chinese J. hebeiensis and J. spinopalpus from the Boso Peninsula on Honshu, Japan (locality #12 in Fig. 1). The second subclade (BS = 91%, PP = 0.99) comprised J. hinumensis Morino, 1993 inhabiting brackish habitats of Japan and J. ikiensis from Iki Island. The third lineage (BS = 100%, PP = 1.0) included Japanese J. mikadoi Tomikawa, Morino & Mawatari, 2003 and four species defined as the J. jesoensis complex by Tomikawa et al (2016): the monophyly of the J. jesoensis complex was well-supported (BS = 97%, PP = 1.0). Jesogammarus paucistulosus and J. bousfieldi formed the last subclade (BS = 98%, PP = 1.0). J. paucistulosus and J. bousfieldi formed a well-supported clade (BS = 100%, PP = 1.0; respectively). The Jesogammarus paucistulosus specimens were divided into two lineages: individuals collected from the southern part of Ibaraki Prefecture (#10, 11) formed a well-supported lineage (BS = 100%, PP = 1.0), and the remainder inhabiting the northern part of Ibaraki (#8) formed the other well-supported clade (BS = 100%, PP = 1.0). The J. bousfieldi specimens were also split into two lineages. Individuals from Mamurogawa (#3) formed a well-supported clade (BS = 100%, PP = 1.0), while the other amphipods inhabiting the southern part of Yamagata Prefecture (#5, 6) grouped with a monophyletic lineage (BS = 100%, PP = 0.99).

Discussion

The species diversity of Jesogammarus inhabiting Japan has been extensively investigated (Tattersall 1922, Schellenberg 1937, Bousfield 1979, Morino 1984, 1985, 1986, 1993, Tomikawa and Morino 2003, Tomikawa et al. 2003, Tomikawa 2015). However, the present findings of the two new Jesogammarus species collected from Japan suggest that the true species diversity of the Japanese Jesogammarus remains unknown.

The freshwater J. bousfieldi described from Yamagata Prefecture has been treated as a population of J. paucisetulosus, which was thought to be widely distributed in Ibaraki, Yamagata and Niigata Prefectures (Tomikawa 2007, Tomikawa and Morino 2012). The latter species was originally described from a spring brooklet in Mito, Ibaraki Prefecture, Japan (Morino 1984). The J. bousfieldi specimens were clearly distinguished from those of J. paucisetulosus collected from Ibaraki Prefecture by the number of marginal setae on dorsal margins of pleonites 1–3. Additionally, our molecular phylogenetic analyses showed that J. bousfieldi was highly diverged from the true J. paucistulosus although they possessed sister-species relationships. Their genetic divergence could be comparable to the detected intraspecific divergences among other Jesogammarus species. Thus, we concluded that J. bousfieldi could be regarded as a distinct new species. Unfortunately, we could not examine specimens of J. paucisetulosus from Niigata Prefecture. A further taxonomic study is necessary to determine the taxonomic position of the population living there.

Contrary to the highly diverged freshwater Jesogammarus species, the number of known species indigenous to brackish habitats is limited: only J. hinumensis has been recorded from brackish lakes and estuaries in Japan (Morino 1993). Therefore, Jesogammarus uchiyamaryui is the second brackish-water species in this genus. This species is morphologically similar to the freshwater J. ikiensis. Although both species are distributed on Iki Island (Tomikawa 2015), they were not collected from the same localities or at the same time on the island (Tomikawa, personal observation). The habitat preferences of these two species seem to be completely different. Moreover, the phylogeny showed that J. uchiyamaryui was not a sister species of J. ikiensis, indicating that they did not share the last common ancestor. Because species diversity of the brackish Jesogammarus remains far from investigated, it is highly possible that additional undescribed species may be found in brackish-water environments within the distributional range of the genus Jesogammarus.

The morphological characteristics and the phylogenetic positions of the two new species raises a question about the validity of the two subgenera, Jesogammarus and Annanogammarus, under the genus Jesogammarus. These two subgenera are characterized only by two morphological characters: 1) accessory lobes of coxal gills of gnathopod 2–pereopod 5 subequal in length or posterior accessory lobe longer than anterior accessory lobe in the subgenus Jesogammarus vs. unequal in length, posterior accessory lobe often rudimentary in the subgenus Annanogammarus; and 2) palmar margin of propodus of female gnathopod 2 with pectinate robust setae in the subgenus Jesogammarus vs. without pectinate robust setae in the subgenus Annanogammarus. Jesogammarus bousfieldi and J. uchiyamaryui bear these subgeneric diagnostic characteristics that are identified with the subgenus Jesogammarus. Contrary to the monophyly of Annanogammarus implicated by previous phylogenetic studies (Tomikawa et al. 2007, Tomikawa 2015), the phylogenies obtained here failed to recover the monophyly of the subgenus Jesogammarus. Although the precise phylogenetic position of J. uchiyamaryui remains uncertain, the findings highlight that the subgeneric classification under the genus Jesogammarus may be abrogated along with synonymizing Annanogammarus with Jesogammarus. Nevertheless, a future systematic study is essential to reveal whether Annanogammarus should be treated as a subjective junior synonym of Jesogammarus.

Key to species of Jesogammarus

1	Accessory lobes of coxal gills on gnathopod 2 and pereopods 3–5 well developed, both anterior and posterior lobes subequal in length or posterior lobe longer than anterior one; palmar margin of propodus of female gnathopod 2 with pectinate setae	2 (subgenus Jesogammarus)
–	Accessory lobes of coxal gills on gnathopod 2 and pereopods 3–5 weakly developed, anterior and posterior lobes unequal in length, often posterior lobe rudimentary; palmar margin of propodus of female gnathopod 2 without pectinate setae	12 (subgenus Annanogammarus)
2	Article 1 of mandibular palp with setae	3
–	Article 1 of mandibular palp without setae	6
3	Dorsal margin of pleonites 1–3 each with 1–2 setae; eye large; article 1 of mandibular palp with 1 robust seta; female pereopods densely setose	J. hinumensis Morino, 1993
–	Dorsal margin of pleonites 1–3 each with more than 4 setae; eye small to medium; article 1 of mandibular palp with 2 or 3 robust setae; female pereopods not densely setose	4
4	Peduncular article 1 of antenna 1 with robust seta on posterodistal corner	J. spinopalpus Morino, 1985
–	Peduncular article 1 of antenna 1 with slender seta on posterodistal corner	5
5	Inner ramus of uropod 3 length 1/4 × outer ramus; inner margin of outer ramus of uropod 3 with 4–6 plumose setae	J. fontanus Hou & Li, 2004
–	Inner ramus of uropod 3 length 1/3 × outer ramus; inner margin of outer ramus of uropod 3 with about 10 plumose setae	J. hebeiensis Hou & Li, 2004
6	Dorsal margin of pereonites 1–3 each with 2 long setae	J. mikadoi Tomikawa, Morino & Mawatari, 2003
–	Dorsal margin of pereonites 1–3 without setae	7
7	Posterodistal corner of peduncular article 2 of antenna 1 without robust seta; posterior margin of peduncular article 2 of antenna 1 with more than 5 setae and/or setal bundles; outer margin of palp article 2 of maxilla 1 without setae	8
–	Posterodistal corner of peduncular article 2 of antenna 1 with robust seta (occasionally lacking); posterior margin of peduncular article 2 of antenna 1 with less than 4 setae and/or setal bundles; outer margin of palp article 2 of maxilla 1 with setae	9
8	Dorsal margins of pleonites 1–3 each with more than 4 setae	J. bousfieldi sp. n.
–	Dorsal margins of pleonites 1–3 each with 0–3 setae	J. paucisetulosus Morino, 1984
9	Accessory lobes of coxal gills on gnathopod 2 and pereopods 3–5 short and straight	J. uchiyamaryui sp. n.
–	Accessory lobes of coxal gills on gnathopod 2 and pereopods 3–5 long and curved	10
10	Dorsal margins of pleonites 1–3 each with 2 or 3 setae; posterior margin of peduncular article 2 of antenna 1 with 3 or 4 setae and/or setal bundls	J. ikiensis Tomikawa, 2015
–	Dorsal margins of pleonites 1–3 each with more than 7 setae; posterior margin of peduncular article 2 of antenna 1 with 2 setae and/or setal bundls	11
11	Palmar margin of propodus of male gnathopod 2 without pectinate setae	J. jesoensis complex
–	Palmar margin of propodus of male gnathopod 2 with pectinate setae	J. ilhoii Lee & Seo, 1992
12	Dorsal margin of pleonite 3 with robust setae; posterior margin of peduncular article 4 and 5 with more than 5 long-setal bundles	J. naritai Morino, 1985
–	Dorsal margin of pleonite 3 without robust setae; posterior margin of peduncular article 4 and 5 with less than 3 short-setal bundles	13
13	Posterodistal corner of bases of pereopods 5–7 with long setae	J. annandalei (Tattersal, 1922)
–	Posterodistal corner of bases of pereopods 5–7 without long setae	14
14	Dorsal margins of pleonites 1–3 each with 2–4 setae	J. fluvialis Morino, 1985
–	Dorsal margins of pleonites 1–3 each with more than 10 setae	15
15	Posterodistal corner of peduncular article 1 of antenna 1 with robust seta; palmar margin of propodus of female gnathopod 2 with simple setae only	J. koreanus Lee & Seo, 1990
–	Posterodistal corner of peduncular article 1 of antenna 1 without robust seta; palmar margin of propodus of female gnathopod 2 with weakly pectinate setae	J. debilis Hou & Li, 2005

Acknowledgements

The authors are grateful to Dr Ronald Vonk (Naturalis) and Dr Michael Ohl (Museum für Naturkunde) for their critical comments on this manuscript. We thank Dr Hiroshi Morino (NSMT) for providing J. paucisetulosus specimens, Noriyoshi Shimura for providing the J. uchiyamaryui specimens, and Tomoko Hirata (Hiroshima University) for supporting the molecular phylogenetic analyses. Thanks are also due to Ryu Uchiyama for providing photographs of live specimens. KT thanks Satoko Tashiro for supporting the field work. This study was partly supported by JSPS KAKENHI Grant Numbers JP25242015, JP25840140, and JP15J00720. The open access publication of this manuscript was supported by the Museum für Naturkunde, Berlin.

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