Two new species add to the diversity of Eoniphargus in subterranean waters of Japan, with molecular phylogeny of the family Mesogammaridae (Crustacea, Amphipoda) Author Shintani, Aki Graduate School of Humanities and Social Sciences, Hiroshima University, 1 - 1 - 1 Kagamiyama, Higashihiroshima, Hiroshima, 739 - 8524, Japan Author Lee, Chi-Woo https://orcid.org/0000-0002-0763-4271 Nakdonggang National Institute of Biological Resources, 137, Donam 2 - gil, Sangju-si, Gyeongsangbuk-do, 37242, Republic of Korea Author Tomikawa, Ko Graduate School of Humanities and Social Sciences, Hiroshima University, 1 - 1 - 1 Kagamiyama, Higashihiroshima, Hiroshima, 739 - 8524, Japan tomikawa@hiroshima-u.ac.jp text Subterranean Biology 2022 2022-08-15 44 21 50 http://dx.doi.org/10.3897/subtbiol.44.86914 journal article http://dx.doi.org/10.3897/subtbiol.44.86914 1314-2615-44-21 1865B08110724900BFC7563C0D29DA7D 27097103DFA85FF0954CAADE72F24005 Eoniphargus iwataorum sp. nov. Figs 6 , 7 , 8 New Japanese name: Iwata-chikayokoebi Type material. Holotype : ♀ 5.6 mm (NSMT-Cr 30782), Sabi River ( 36.898181°N , 140.012153°E ), Imaizumi, Ohtawara, Tochigi Prefecture, Japan, collected by Y. Iwata on 27 January 2019. Paratype : ♀ 5.3 mm (NSMT-Cr 30783; G1751), ♀ 6.0 mm (NSMT-Cr 30784), data same as for the holotype. Diagnosis. Urosomite 3 without dorsal setae. Epimeral plates 2-3 each with ventral robust seta. Peduncular article 1 of antenna 1 with robust seta on posterodistal corner. Antenna 2 with peduncular article 2 gland cone not exceeding end of article 3. Mandible with 5-dentate left incisor; left lacinia mobilis 4-dentate, right one bifid with many teeth. Inner plate of maxilla 1 with eight plumose setae. Inner plate of maxilla 2 with seven facial seta in oblique row. Peduncle of pleopod 3 with seta. Uropod 1 with peduncle bearing basofacial robust setae. Uropod 3 with inner ramus 0.25 times as long as outer ramus; outer ramus 2-ariticulate, with plumose setae on medial margin. Telson almost as long as width, cleft for 67% of length. Etymology. The specific epithet was derived from the names of Mr. Yasuyuki Iwata and Mr. Tomofumi Iwata, who collected the specimens of this new species. Description. Female holotype, NSMT-Cr 30782. Head (Fig. 6A ) as long as pereonites 1 and 2 combined; eyes absent; inferior antennal sinus distinct with rounded angle. Dorsal margins of pleonites 1-3 (Fig. 6B-D ) each with four setae. Posterodistal corners of epimeral plates 1-3 (Fig. 6E-G ) weakly produced; ventral margin of epimeral plate 1 without setae, epimeral plates 2 and 3 each with ventral robust seta; posterior margins of epimeral plates 1-3 each with two setae. Dorsal margin of urosomite 1 (Fig. 6H ) with slender setae; urosomite 2 (Fig. 6I ) with dorsal robust setae; urosomite 3 (Fig. 6J ) without dorsal setae. Figure 6. Eoniphargus iwataorum sp. nov., female holotype (NSMT-Cr 30782) A head, lateral view B-D dorsal margins of pleonites 1-3, dorsal views E-G epimeral plates 1-3, lateral views H-J dorsal margins of urosomites 1-3, dorsal views K antenna 1 (some flagellar articles are omitted), lateral view L antenna 2 (some flagellar articles are omitted), lateral view M upper lip, anterior view N right mandible, medial view O incisor and lacinia mobilis of right mandible, medial view P incisor and lacinia mobilis of left mandible, lateral view Q lower lip, anterior view R maxilla 1, dorsal view S apical robust setae on outer plate of maxilla 1, dorsal view T maxilla 2, dorsal view. Antenna 1 (Fig. 6K ) length 0.25 times as long as body; length ratio of peduncular articles 1-3 in 1.0: 0.8: 0.4; posterodistal corner of peduncular article 1 with robust seta; accessory flagellum 4-articulate; primary flagellum 27-articulate. Antenna 2 (Fig. 6L ) length 0.7 times as long as antenna 1; peduncular article 4 slightly shorter than article 5; flagellum 22-articulate; calceoli absent. Upper lip (Fig. 6M ) with rounded apical margin bearing fine setae. Mandibles (Fig. 6N-P ) with left and right incisors comprising five and six teeth, respectively; left lacinia mobilis comprising four teeth, right lacinia mobilis bifid with many teeth; molar process triturative with plumose seta; length ratio of palp articles 1-3 in 1.0: 2.0: 1.5; palp article 1 without setae; palp article 2 with eight marginal setae; palp article 3 with pair of A-setae, several D-setae and E-setae, lateral face with fine setae. Lower lip (Fig. 6Q ) lacking inner lobes; outer lobes broad, shoulder rounded, with fine setae. Maxilla 1 (Fig. 6R, S ) with elliptical inner lobe, bearing eight plumose setae on medial margin; outer plate rectangular, with 11 serrate robust setae apically; palp 2-articulate, article 1 without setae, article 2 with five robust setae and slender plumose seta apically. Maxilla 2 (Fig. 6T ) with inner plate bearing seven plumose setae in oblique row. Maxilliped (Fig. 7A-C ) with inner plate exceeding end of palp article 1, subquadrate, bearing three subapical robust setae and medial robust seta; outer plate ovate, reaching middle of palp article 2, with row of robust setae along apical to medial margins; palp 4-articulate, article 2 longest with medial setae, nail of article 4 distinct. Figure 7. Eoniphargus iwataorum sp. nov., female holotype (NSMT-Cr 30782) A maxilliped, dorsal view B inner plate of maxilliped, dorsal view C outer plate of maxilliped, dorsal view D gnathopod 1, lateral view E palmar margin and dactylus of gnathopod 1, medial view F gnathopod 2, lateral view G palmar margin and dactylus of gnathopod 2, medial view H pereopod 3, lateral view I dactylus of pereopod 3, lateral view J pereopod 4, lateral view K pereopod 5, lateral view L pereopod 6, lateral view. Gnathopod 1 (Fig. 7D, E ) with subquadrate coxa bearing setae along anterior to ventral margins; anterior and posterior margins of basis with long setae; carpus length 0.9 times as long as length of propodus and 1.4 times width of carpus; propodus length 1.7 times width, palmar margin weakly serrate, oblique, with three medial and one lateral robust setae; dactylus reaching posterodistal corner of propodus. Gnathopod 2 (Fig. 7F, G ) with coxa expanded proximally bearing setae along anterior to ventral margins; posterior margin of basis with long setae; carpus length 1.2 times as long as length of propodus and 2.8 times width of carpus; propodus length 2.2 times width, palmar margin weakly serrate, almost vertical, with two medial and two lateral robust setae; dactylus reaching posterodistal corner of propodus. Pereopod 3 (Fig. 7H, I ) with subquadrate coxa, proximally expanded, bearing setae along anterior to ventral margins; posterior margin of basis with long setae. Pereopod 4 (Fig. 7J ) with coxa bearing setae along anterior to ventral margins, posteroproximally concave; posterior margin of basis with long setae. Pereopod 5 (Fig. 7K ) with bilobed coxa bearing seta on posterior lobe; anterior margin of basis with robust setae, posterodistal corner weakly lobate. Pereopod 6 (Fig. 7L ) with bilobed coxa bearing seta on anterior and posterior lobes; basis with robust setae on anterior margin, posterodistal corner weakly lobate. Pereopod 7 (Fig. 8A-C ) with elliptical basis bearing robust setae on anterior margin, posterodistal corner weakly lobate. Figure 8. Eoniphargus iwataorum sp. nov., female holotype (NSMT-Cr 30782) A, B pereopod 7, lateral views C dactylus of pereopod 3, lateral view D coxal gill 4, lateral view E coxal gill 6, lateral view F peduncle of pleopod 1, lateral view G pleopod 2, medial view H peduncle of pleopod 3, lateral view I retinacula of pleopod 2, medial view J uropod 1, dorsal view K uropod 2, dorsal view L uropod 3, ventral view M telson, dorsal view. Coxal gills (Fig. 8D, E ) ovate with stalks on gnathopod 2 and pereopods 3-6. Pleopods 1-3 (Fig. 8F-I ) with peduncles longer than rami, bearing distal seta on pleopods 1 and 2 and proximal seta on pleopod 3; retinacula paired (Fig. 8I ); mediobasal margin of inner ramus with bifid plumose setae; rami well developed. Uropod 1 (Fig. 8J ) with peduncle bearing three basofacial robust setae and dorsal robust setae; inner ramus length 0.7 times as long as peduncle, with two medial and one lateral robust setae, and ventroproximal seta; outer ramus length 0.9 times as long as inner ramus, with two robust setae on medial margin. Uropod 2 (Fig. 8K ) with peduncle bearing dorsal robust setae; inner ramus as long as peduncle, bearing two medial robust setae and ventroproximal slender seta; outer ramus length 0.7 times as long as inner ramus, without marginal setae. Uropod 3 (Fig. 8L ) with peduncle length 0.3 times as long as outer ramus, bearing robust setae on distal edge; inner ramus length 0.2 times as long as outer ramus, with seta on medial margin; outer ramus 2-articulate, proximal article with plumose setae on medial margin and robust setae on medial and lateral margins, terminal article length 0.2 times as long as proximal article with subapical setae. Telson (Fig. 8M ) length slightly shorter than wide, each lobe with two lateral and three apical robust setae and two dorsolateral penicillate setae, cleft for 67%. Distribution and environment. The species is known only from its type locality in the Sabi River, Tochigi Prefecture, Japan. Remarks. Eoniphargus iwataorum sp. nov. is similar to E. kojimai but differs from the latter in the following features (features of E. kojimai in parentheses): urosomite 3 without robust setae on dorsal margin (bearing robust setae), maxilla 2 with inner plate bearing seven setae in oblique row (nine setae), and uropod 2 without robust seta on lateral margin of outer ramus (bearing robust seta).