taxonID	type	description	language	source
F8431828103B53DDB0F3E36DBE786A72.taxon	description	Figs 2, 3, 4, 5 [New Japanese name: Kourai-iso-yokoebi]	en	Yoshimura, Hiro, Lee, Chi-Woo, Tomikawa, Ko (2025): Taxonomy of the genus Elasmopus (Crustacea, Amphipoda) in Japan and South Korea, with description of a new species. ZooKeys 1261: 307-335, DOI: 10.3897/zookeys.1261.162923
F8431828103B53DDB0F3E36DBE786A72.taxon	diagnosis	Diagnosis. Epimeral plate 3 posteroventral corner without distinct projection. Antenna 1 peduncles bearing slender setae on lateral and medial margins, with bi-articulate accessory flagellum. Antenna 2 flagellum articles distinctly broader than long. Mandibular palp article 3 short. Male gnathopod 2 propodus posterior margin with a few clusters of slender setae, palmar margin with subtriangular process near hinge of dactylus, mid-palmar margin with subrectangular hump. Length of setae on coxae 2 and 3 shorter than width of each coxa. Pereopods 5 – 7 basis posterior margin smooth, without long setae. Telson cleft, border than long; lobe trapezoid, with shallow incision at apex, each lobe bearing one plumose and two or three robust setae apically.	en	Yoshimura, Hiro, Lee, Chi-Woo, Tomikawa, Ko (2025): Taxonomy of the genus Elasmopus (Crustacea, Amphipoda) in Japan and South Korea, with description of a new species. ZooKeys 1261: 307-335, DOI: 10.3897/zookeys.1261.162923
F8431828103B53DDB0F3E36DBE786A72.taxon	description	Description of male (NSMT - Cr 33062). Body (Fig. 2 A): smooth, not carinate, with a few short setae dorsally on pereon and abdomen. Head: eyes oval; lateral cephalic lobe broad, anteroventral margin with notch; dorsal surface with a few short setae. Epimeral plate 3 (Fig. 3 A): ventral margin with seven robust setae, posterior margin with five short setae, posteroventral corner without distinct projection. Antenna 1: length 0.6 × body length; peduncular articles 1 – 3 with slender setae on lateral and medial margins; accessory flagellum (Fig. 3 B) bi-articulate, reaching 2 / 3 of primary flagellar article 1, accessory flagellar article 2 tiny; primary flagellum 21 - articulate, with slender setae. Antenna 2 (Fig. 3 C): length 0.4 × antenna 1; peduncular articles 4 and 5 almost same length, with slender setae on lateral and medial margins; flagellum 8 - articulate, articles 1 – 5 shorter than wide, with slender setae. Mandible (Fig. 3 D, E) with left and right incisors with two and four teeth, respectively; both left and right lacinia mobilis with five teeth; accessory setal row consisting of four setae on each of left and right mandibles; molar process well developed, triturative; palp well developed, tri-articulate; palp article 1 without setae, article 2 with six setae, article 3 falcate, length 2.5 × width. Gnathopod 1 (Fig. 4 A): subchelate; coxa anteroventral corner weakly produced, ventral margin with long and short setae; basis with long setae on posterior margin and medial surface; carpus subequal in length to propodus, with slender seta on anterodistal corner, with dense setae on posterior margin and medial surface; propodus with three and six clusters of setae on anterior margin and medial surface, respectively, posterior margin with row of slender and robust setae, palmar margin almost transverse, minutely serrate, with rows of robust setae on medial and lateral palmar submargins. Gnathopod 2 (Figs 4 B, 5 B): subchelate; coxa with long and short setae on ventral margin, length of the longest seta 0.6 × width of coxa; basis with long setae on posterior margin; carpus with dense setae on posterior margin; propodus with four setae on anterolateral submargin, posterior margin with nine clusters of slender setae, palmar margin with subrectangular hump at midpoint and robust seta at proximal end where tip of dactylus contacts, lateral palmar margin with subtriangular hump near hinge of dactylus. Telson (Fig. 3 F): broader than long, cleft for 60 % of length; lobe trapezoid, with shallow incision at apex, each lobe bearing one plumose and three robust setae apically, lateral margin of each lobe with none or one plumose setae.	en	Yoshimura, Hiro, Lee, Chi-Woo, Tomikawa, Ko (2025): Taxonomy of the genus Elasmopus (Crustacea, Amphipoda) in Japan and South Korea, with description of a new species. ZooKeys 1261: 307-335, DOI: 10.3897/zookeys.1261.162923
F8431828103B53DDB0F3E36DBE786A72.taxon	description	Description of female (NSMT - Cr 33063), sexually dimorphic characters. Gnathopod 1 (Fig. 4 C): propodus anterior margin with one single and three clusters of setae, medial surface with five clusters of setae. Gnathopod 2 (Fig. 4 D): propodus with nine and eight clusters of setae on anteromedial margin and medial surface, respectively, palmar margin almost straight, with minutely serrate on the distal one third of the palmar margin. Oostegites on gnathopod 2 and pereopods 3 – 5, slender with long setae.	en	Yoshimura, Hiro, Lee, Chi-Woo, Tomikawa, Ko (2025): Taxonomy of the genus Elasmopus (Crustacea, Amphipoda) in Japan and South Korea, with description of a new species. ZooKeys 1261: 307-335, DOI: 10.3897/zookeys.1261.162923
F8431828103B53DDB0F3E36DBE786A72.taxon	distribution	Distribution. South Korea: Busan (present study); Ulleungdo Island in Gyeongsangbuk-do (Kim and Kim 1991; Shin et al. 2025); Chujado Islands in Jeju-do (Kim et al. 2023). Japan: Chiba, Kanagawa, and Tottori; Shikinejima Island in Tokyo (present study) (Fig. 1).	en	Yoshimura, Hiro, Lee, Chi-Woo, Tomikawa, Ko (2025): Taxonomy of the genus Elasmopus (Crustacea, Amphipoda) in Japan and South Korea, with description of a new species. ZooKeys 1261: 307-335, DOI: 10.3897/zookeys.1261.162923
A6AB1033296A5F529BB1FAE054DAA466.taxon	description	Figs 6, 7, 8, 9, 10, 11, 12 [New Japanese name: Sewata-iso-yokoebi]	en	Yoshimura, Hiro, Lee, Chi-Woo, Tomikawa, Ko (2025): Taxonomy of the genus Elasmopus (Crustacea, Amphipoda) in Japan and South Korea, with description of a new species. ZooKeys 1261: 307-335, DOI: 10.3897/zookeys.1261.162923
A6AB1033296A5F529BB1FAE054DAA466.taxon	diagnosis	Diagnosis. Epimeral plate 3 posteroventral corner produced into well-developed acute spine. Antenna 1 peduncles bearing slender setae on lateral and medial margins, with tri-articulate accessory flagellum. Mandibular palp article 3 short. Gnathopod 2 carpus anterodistal corner with slender setae, length of the longest seta reaching 0.8 – 1.1 and 0.9 – 1.1 × width of carpus in male and female. Male gnathopod 2 propodus posterior margin and inner surface with dense slender setae, length of the longest seta reaching 0.9 × width of propodus, palmar margin with trapezoidal hump near hinge of dactylus, mid-palmer margin with ridge. Pereopods 5 – 7 basis posterior margin smooth, without long setae. Telson cleft, border than long; lobe trapezoid, with shallow incision at apex, each lobe bearing one plumose and 4 – 6 robust setae apically.	en	Yoshimura, Hiro, Lee, Chi-Woo, Tomikawa, Ko (2025): Taxonomy of the genus Elasmopus (Crustacea, Amphipoda) in Japan and South Korea, with description of a new species. ZooKeys 1261: 307-335, DOI: 10.3897/zookeys.1261.162923
A6AB1033296A5F529BB1FAE054DAA466.taxon	description	Description of male (holotype, NSMT - Cr 33064). Body (Fig. 7 A): smooth, not carinate, with a few short setae dorsally on pereon and abdomen. Head: eyes oval; lateral cephalic lobe broad, anteroventral margin with notch; dorsal surface with a few short setae. Epimeral plates 1 – 3 (Fig. 7 B – D): each ventral margin with one cluster and one single robust seta, two clusters and one single robust seta, and two clusters and five robust setae, respectively; each posterior margin with three or four, four and four short setae, respectively; posteroventral corner of epimeral plates 1 and 2 weakly produced, epimeral plate 3 produced into well-developed acute spine. Antenna 1 (Fig. 8 A): length 0.55 × body length; peduncular articles 1 – 3 in length ratio of 1.1: 1.0: 0.6, with slender setae on lateral and medial margin; peduncular article 1 with three robust setae on posteroproximal margin, robust seta on posterodistal corner; accessory flagellum tri-articulate, accessory flagellar article 3 tiny; primary flagellum 34 - articulate, with slender setae. Antenna 2 (Fig. 8 B): length 0.5 × antenna 1; peduncular article 2 with six short spines on anterodistal corner, gland cone of peduncular article 2 exceeding distal margin of peduncular article 3; peduncular article 4 slightly longer than 5, with slender setae on lateral and medial margins; flagellum 13 - articulate, with slender setae. Mouthparts. As holotype upper lip missing, that of paratype (male, 9.9 mm, NSMT - Cr 33066) illustrated. Upper lip (Fig. 8 C) with rounded anterior margin, bearing fine setae. Mandible (Fig. 8 D – F) with left and right incisors two and four teeth, respectively; left lacinia mobilis five teeth and right lacinia mobilis four teeth; accessory setal row three setae on the left and four setae on the right; molar process well developed, triturative; palp (Fig. 8 F) well developed, tri-articulate; palp article 1 without setae, article 2 with ten setae, article 3 falcate, length 3.0 × width. Lower lip (Fig. 8 G) with outer lobes laterally expanded, bearing apical setae; inner lobes ovate, apically covered with setae. Maxilla 1 (Fig. 8 H) with inner plate bearing two plumose setae apically; outer plate with seven robust dentate setae; palp bi-articulate, article 1 marginally bare, article 2 with numerous apical and subapical setae, outer margin bare. Maxilla 2 (Fig. 8 I) with inner plate bearing long apical setae, with setae on outer and inner margins; outer plate bearing long apical setae, with setae on outer margin. Maxilliped (Fig. 8 J) with inner plate bearing plumose setae apically; outer plate obovate, with spatula plumose setae on apical and inner margins, reaching more than half of palp article 2; palp article 1 with two setae on inner margin, with seta on outer margin; palp article 2 slender, lined with setae on inner margin, outer margin bare; nail of palp article 4 distinct. Gnathopod 1 (Fig. 9 A – D): subchelate; coxa anteroventral corner weakly produced, anterior margin weakly concave, ventral margin with long and short setae; basis with long setae on posterior margin and medial surface; carpus subequal in length to propodus, with slender setae on anterodistal corner, with dense pinnate sided setulated setae on medial surface and posterior margin; propodus with six clusters of setae on anterior margin, with seven clusters of setae on medial surface; palmar margin (Fig. 9 C, D) almost transverse, minutely serrate, with rows of robust setae on medial and lateral palmar submargins, palmar corner with two long robust setae; dactylus with slender seta on anteroproximal margin, with six small setae on lateral margin, with spatulate seta and slender seta laterally at the base of nail. Gnathopod 2 (Fig. 9 E – G): subchelate; coxa with long and short setae on ventral margin, of which two long setae retrorse; basis with long setae on posterior margin; merus distoventral corner subquadrate bearing long setae; carpus with slender setae on anterodistal corner, length of these setae 0.9 × width of carpus, with dense setae on posterior margin; propodus with five clusters, two pairs and two single setae on anterolateral submargin, length of these setae 0.4 × width of propodus, anteromedial submargin with eight clusters of setae; lateral palmar margin weakly concave with trapezoidal hump (Fig. 9 G) on near insertion of dactylus, with one clusters, three pairs and one single setae on lateral surface, with six and seven robust setae on lateral and medial margins, respectively; mid-palmar margin with ridge; posterior margin with row of plumose setae, the proximal seta longer than the distal seta, length of the longest seta 0.9 × width of propodus; dactylus strongly curved, subacute, length 0.6 × length of propodus, with seta on anteroproximal margin. Pereopod 3 (Fig. 10 A): coxa longer than broad, ventral margin with numerous short and a few long setae, of which long seta retrorse; posterior margins of basis with long slender and robust setae, merus with slender setae, carpus and propodus with robust and slender setae; dactylus with plumose seta on anteroproximal margin, with one robust and two slender setae at the base of nail. Pereopod 4 (Fig. 10 B): coxa expanded with posterior concavity, ventral margin arched bearing numerous short and a few long setae, of which long seta retrorse; posterior margins of basis with long slender and robust setae, merus with slender setae, carpus and propodus with robust and slender setae; dactylus with plumose seta on anteroproximal margin, with one robust and two slender setae at the base of nail. Pereopod 5 (Fig. 10 C): coxa bilobed, ventral margin of posterior lobe with two robust setae, posterior margin of posterior lobe with five short setae; basis broad, subrectangular, posterior margin smooth, with numerous short setae; anterior and posterior margins of carpus with robust setae; propodus with robust setae on anterior margin, with one cluster setae on posteromedial submargin; dactylus with plumose seta on posteroproximal margin, with one robust and two slender setae at the base of nail. Pereopod 6 (Fig. 10 D): coxa bilobed, anterior margin of anterior lobe with slender setae, ventral margin of posterior lobe with three robust setae, posterior margin of posterior lobe with five short setae; basis weakly expanded proximally, tapering distally, posterior margin smooth with numerous short setae; anterior margin of carpus with robust and slender setae, posterior margin with robust setae; anterior margin of propodus with robust setae, with two clusters setae on posteromedial submargin; dactylus with plumose seta on posteroproximal margin, with one robust seta and two slender setae at the base of nail. Pereopod 7 (Fig. 10 E): coxa rounded, with slender setae on anterior and short setae on posterior margins; basis expanded, subovate, posterior margin rounded, smooth, with numerous short setae; anterior and posterior margins of carpus with robust and slender setae; anterior margin of propodus with robust and slender setae, with three clusters setae on posteromedial submargin; dactylus with plumose seta on posteroproximal margin, with one robust and two slender setae at the base of nail. Coxal gills on gnathopod 2 and pereopods 3 – 6. Pleopods (Fig. 10 F – K): peduncles with long setae, inner distal corner of peduncle with two retinacula (Fig. 10 G, I, K), peduncle of pleopod 3 broader than pleopod 1 and 2. Uropods. Uropod 1 (Fig. 11 A): peduncle length 1.2 × length of outer ramus, with six dorsolateral, seven dorsomedial and one basofacial robust setae; outer ramus slightly shorter than inner ramus, medial and lateral margins each with four robust setae, distal part with four robust setae; inner ramus medial and lateral margins each with four robust setae, distal part with five robust setae. Uropod 2 (Fig. 11 B): peduncle length 0.9 × length of outer ramus; outer ramus slightly shorter than inner ramus, with three and five robust setae on medial and lateral margins, respectively, distal part with four robust setae; inner ramus five and four robust setae on medial and lateral margins, respectively, distal part with five robust setae. Uropod 3 (Fig. 11 C): peduncle length 0.8 × length of outer ramus, with pair of robust setae on outer margin; rami distally truncated; outer ramus length 1.5 × length of inner ramus, with three and one clusters of robust setae on lateral and distal margins, respectively, with robust seta and one pair of robust setae on medial margin and surface, respectively; inner ramus with cluster of robust setae distally and two robust setae on medial margin. Telson (Fig. 11 D): broader than long, cleft for 75 % of length; lobe trapezoid, with shallow incision at apex, each lobe bearing one plumose five robust setae apically, lateral margin of each lobe with one or two plumose setae.	en	Yoshimura, Hiro, Lee, Chi-Woo, Tomikawa, Ko (2025): Taxonomy of the genus Elasmopus (Crustacea, Amphipoda) in Japan and South Korea, with description of a new species. ZooKeys 1261: 307-335, DOI: 10.3897/zookeys.1261.162923
A6AB1033296A5F529BB1FAE054DAA466.taxon	description	Description of female (paratype, NSMT - Cr 33068), sexually dimorphic characters. Gnathopod 1 (Fig. 11 E, F): propodus anterior margin with 1 single and 4 clusters of setae, medial surface with 6 clusters of setae. Gnathopod 2 (Fig. 11 G, H): slender setae on carpus anterodistal corner reaching width of carpus; propodus with two clusters, three pairs, and two 2 single setae on anterolateral submargin, length of these setae 0.7 × width of propodus, anteromedial submargin with 13 clusters; palmar margin (Fig. 11 H) almost straight, with minutely serrate on the distal 1 / 5 of the palmar margin. Pereopod 3 (Fig. 11 I): basis with slender setae on anterior margin, the longest seta 0.8 × width of basis. Oostegites on gnathopod 2 and pereopods 3 – 5, slender with long setae.	en	Yoshimura, Hiro, Lee, Chi-Woo, Tomikawa, Ko (2025): Taxonomy of the genus Elasmopus (Crustacea, Amphipoda) in Japan and South Korea, with description of a new species. ZooKeys 1261: 307-335, DOI: 10.3897/zookeys.1261.162923
A6AB1033296A5F529BB1FAE054DAA466.taxon	distribution	Distribution. Japan: Chiba, Kanagawa, Wakayama, and Tottori (present study) (Fig. 1).	en	Yoshimura, Hiro, Lee, Chi-Woo, Tomikawa, Ko (2025): Taxonomy of the genus Elasmopus (Crustacea, Amphipoda) in Japan and South Korea, with description of a new species. ZooKeys 1261: 307-335, DOI: 10.3897/zookeys.1261.162923
A6AB1033296A5F529BB1FAE054DAA466.taxon	etymology	Etymology. The specific name lumbiniger, from the Latin lumbus (= loin, lower back) and niger (= black), refers to the dark coloration along the dorsal midline of male pleonite 3 and urosomite 1 in life (Fig. 6 A). The Japanese name is derived from this band, which resembles a vein running along the back of a shrimp, known as “ Sewata ”.	en	Yoshimura, Hiro, Lee, Chi-Woo, Tomikawa, Ko (2025): Taxonomy of the genus Elasmopus (Crustacea, Amphipoda) in Japan and South Korea, with description of a new species. ZooKeys 1261: 307-335, DOI: 10.3897/zookeys.1261.162923
967A4C8DAA6D5A269D40336937981218.taxon	description	Figs 13, 14, 15 [New Japanese name: Mukuinu-iso-yokoebi]	en	Yoshimura, Hiro, Lee, Chi-Woo, Tomikawa, Ko (2025): Taxonomy of the genus Elasmopus (Crustacea, Amphipoda) in Japan and South Korea, with description of a new species. ZooKeys 1261: 307-335, DOI: 10.3897/zookeys.1261.162923
967A4C8DAA6D5A269D40336937981218.taxon	diagnosis	Diagnosis. Epimeral plate 3 posterior margin weakly serrated. Antenna 1 peduncles bearing slender setae on lateral and medial margins, with bi- or tri-articulate accessory flagellum. Mandibular palp article 3 short. Gnathopod 2 carpus anterodistal corner with slender setae, length of the longest seta reaching 0.3 – 0.6 and 0.4 – 0.6 × width of carpus in male and female. Male gnathopod 2 propodus posterior margin and inner surface with dense slender setae, length of the longest seta 0.9 × width of propodus, palmar margin with semicircular hump near hinge of dactylus, mid-palmer margin with ridge. Pereopods 5 – 7 basis posterior margin smooth, without long setae. Telson cleft, border than long; lobe trapezoid, with shallow incision at apex, inner apical corner rounded and produced, each lobe bearing one plumose and one or two robust setae apically.	en	Yoshimura, Hiro, Lee, Chi-Woo, Tomikawa, Ko (2025): Taxonomy of the genus Elasmopus (Crustacea, Amphipoda) in Japan and South Korea, with description of a new species. ZooKeys 1261: 307-335, DOI: 10.3897/zookeys.1261.162923
967A4C8DAA6D5A269D40336937981218.taxon	description	Description of male (NSMT - Cr 33081). Body (Fig. 13 B): smooth, not carinate, with a few short setae dorsally on pereon and abdomen. Head: eyes oval; lateral cephalic lobe broad, anteroventral margin with notch; dorsal surface with a few short setae. Epimeral plate 3 (Fig. 14 A): ventral margin with two pairs and four single robust setae, posterior margin weakly serrated, with four short setae. Antenna 1: length 0.6 × body length; peduncular articles 1 – 3 with slender setae on lateral and medial margins; accessory flagellum (Fig. 14 B) tri-articulate, reaching to distal margin of primary flagellar article 1, accessory flagellar article 3 tiny; primary flagellum 28 - articulate, with slender setae. Mandible (Fig. 14 C – E) with left and right incisors three and four teeth, respectively; left and right lacinia mobilis three and four teeth, respectively; accessory setal row consisting of four setae on each of left and right mandibles; molar process well developed, triturative; palp well developed, tri-articulate; article 2 with seven setae, article 3 falcate, length 3.2 × width. Gnathopod 1 (Fig. 15 A): subchelate; coxa anteroventral corner weakly produced; basis with long setae on posterior margin and medial surface; carpus subequal in length to propodus, with slender seta on anterodistal corner, with dense setae on posterior margin and medial surface; propodus with four and five clusters of setae on anterior margin and medial surface, respectively, posterior margin with row of slender and robust setae, palmar margin almost transverse, minutely serrate, with rows of robust setae on medial and lateral palmar submargins. Gnathopod 2 (Fig. 15 B): subchelate; basis with long setae on posterior margin; carpus with slender setae on anterodistal corner, length of these setae reaching 0.6 × width of carpus, with dense setae on posterior margin; propodus with one cluster, one pair and three single setae on anterolateral submargin, length of these setae reaching 0.2 × width of propodus, with nine clusters of setae on anteromedial submargin, lateral palmar margin with hump on near insertion of dactylus, mid-palmar margin with ridge, posterior margin with row of plumose setae, the proximal seta longer than the distal seta, length of the longest seta reaching 0.9 × width of propodus. Telson (Fig. 13 F): broader than long, cleft for 65 % of length; lobe trapezoid, with shallow incision at apex, inner apical corner rounded and produced, each lobe bearing one plumose and two robust setae apically, lateral margin of each lobe with one plumose seta.	en	Yoshimura, Hiro, Lee, Chi-Woo, Tomikawa, Ko (2025): Taxonomy of the genus Elasmopus (Crustacea, Amphipoda) in Japan and South Korea, with description of a new species. ZooKeys 1261: 307-335, DOI: 10.3897/zookeys.1261.162923
967A4C8DAA6D5A269D40336937981218.taxon	description	Description of female (NSMT - Cr 33083), sexually dimorphic characters. Antenna 1: accessory flagellum (Fig. 14 G) bi-articulate. Gnathopod 1 (Fig. 15 C): propodus anterior margin with three clusters of setae, medial surface with five clusters of setae. Gnathopod 2 (Fig. 15 D): slender setae on carpus anterodistal corner 0.6 × width of carpus; propodus with four slender setae on anterolateral submargin, the longest setae 0.4 × width of propodus, with eight and ten clusters of setae on anteromedial margin and medial surface, respectively; palmar margin almost straight, with minutely serrate on the distal 2 / 5 of the palmar margin.	en	Yoshimura, Hiro, Lee, Chi-Woo, Tomikawa, Ko (2025): Taxonomy of the genus Elasmopus (Crustacea, Amphipoda) in Japan and South Korea, with description of a new species. ZooKeys 1261: 307-335, DOI: 10.3897/zookeys.1261.162923
967A4C8DAA6D5A269D40336937981218.taxon	distribution	Distribution. Japan: Shizuoka, Izu Islands (Shikinejima Island and Hachijojima Island), Tokyo (present study); Okinawa Island, Okinawa (Sir and White 2022; present study) (Fig. 1).	en	Yoshimura, Hiro, Lee, Chi-Woo, Tomikawa, Ko (2025): Taxonomy of the genus Elasmopus (Crustacea, Amphipoda) in Japan and South Korea, with description of a new species. ZooKeys 1261: 307-335, DOI: 10.3897/zookeys.1261.162923
