Jesogammarus (Jesogammarus) bousfieldi, 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 : 191-193

Jesogammarus (Jesogammarus) bousfieldi sp. n. 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. 3 A–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. 3 G–I) with 8, 6, and 2 robust setae associated with slender setae on dorsal margins.

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).

Mouthparts. Upper lip (= labrum) (Fig. 3M) with rounded distal margin, bearing fine setae. Mandibles (Fig. 3 N–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.

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.

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. 5 D–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.

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. 7 A–C).

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.

Remarks.

Jesogammarus bousfieldi resembles Jesogammarus 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, Jesogammarus bousfieldi differs from Jesogammarus paucisetulosus by the number of setae on the dorsal margins of pleonites 1-3: each pleonite with more than 4 setae in Jesogammarus bousfieldi vs. 0-3 in Jesogammarus paucisetulosus .