Jesogammarus (Jesogammarus) uchiyamaryui, Tomikawa, Ko, Nakano, Takafumi & Hanzawa, Naoto, 2017

Tomikawa, Ko, Nakano, Takafumi & Hanzawa, Naoto, 2017, Two new species of Jesogammarus from Japan (Crustacea, Amphipoda, Anisogammaridae), with comments on the validity of the subgenera Jesogammarus and Annanogammarus, Zoosystematics and Evolution 93 (2), pp. 189-210 : 193-196

Jesogammarus (Jesogammarus) uchiyamaryui sp. n. 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. 10 A–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. 10 G–I) with 10, 6, and 6 robust setae on dorsal margins.

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).

Mouthparts. Upper lip (= labrum) (Fig. 10M) with rounded distal margin, bearing fine setae. Mandibles (Fig. 10 N–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-se tae, 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.

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.

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. 12 D–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.

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. 13 H–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 Jesogammarus 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, Jesogammarus uchiyamaryui differs from Jesogammarus ikiensis by the following features (features of Jesogammarus 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 Jesogammarus 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 Jesogammarus 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.

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: Jesogammarus 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.

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 Jesogammarus hebeiensis and Jesogammarus spinopalpus from the Boso Peninsula on Honshu, Japan (locality #12 in Fig. 1). The second subclade (BS = 91%, PP = 0.99) comprised Jesogammarus hinumensis Morino, 1993 inhabiting brackish habitats of Japan and Jesogammarus ikiensis from Iki Island. The third lineage (BS = 100%, PP = 1.0) included Japanese Jesogammarus mikadoi Tomikawa, Morino & Mawatari, 2003 and four species defined as the Jesogammarus jesoensis complex by Tomikawa et al (2016): the monophyly of the Jesogammarus jesoensis complex was well-supported (BS = 97%, PP = 1.0). Jesogammarus paucistulosus and Jesogammarus bousfieldi formed the last subclade (BS = 98%, PP = 1.0). Jesogammarus paucistulosus and Jesogammarus 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 Jesogammarus 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).