Four species of the genus Stephonyx (Crustacea: Amphipoda: Uristidae) from Japan, with description of a new species Author Narahara, Yukiko Author Tomikawa, Ko Author Torigoe, Kenji text Journal of Natural History 2012 J. Nat. Hist. 2012-06-30 46 23 - 24 1477 1507 http://dx.doi.org/10.1080/00222933.2012.675598 journal article 10.1080/00222933.2012.675598 1464-5262 5200209 B4D66BC0-1866-4F68-95C0-2A1584B6141B Stephonyx laqueus ( Barnard, 1967 ) (Japanese name: Tsumamisokoebi ) ( Figures 12–14 ) Euonyx laqueus Barnard, 1967: 55 , figs 23–24: Sekiguchi and Yamaguchi , 1983: 7 , fig. 4. Stephonyx laqueus Diffenthal and Horton, 2007: 39 (key); Senna and Serejo, 2007: 13 (key). Material examined NSMT-Cr 22034, one male ( 19.6 mm ), NSMT-Cr 22033, one female ( 20.1 mm ), Sea of Okhotsk , 44 ◦ 35.4 ′ N , 144 ◦ 42.1 ′ E , baited trap , 1551–1578 m , bottom at 14:34 on 2 August 2009 , R / V Soyo-maru , Soyo-2009, St-trap 3 ( Sea of Okhotsk ), 3 August 2009 , coll. H. Yamasaki. Description of male Head ( Figure 12A ) deeper than long, lateral cephalic lobe rounded; rostrum absent; eyes L-shaped. Epimeral plates 1–3 ( Figure 14D–F ) with anteroventral corners rounded, with setae; posterior margin of plate 1 convex; posteroventral corner of plate 2 with tooth and corner of plate 3 weakly pointed. Antenna 1 ( Figure 12B, C ) 0.2 times body length, peduncular articles 1–3 length ratio of 1.0: 0.3: 0.5; accessory flagellum eight-articulate; primary flagellum 27-articulate, calceoli present on article 18; callynophore well-developed, 26 rows, two fields. Antenna 2 ( Figure 12D ) 1.7 times antenna 1; anterior margins of peduncular articles 4 and 5 with brush setae, peduncular articles 4 and 5 not swollen; flagellum 57-articulate, calceoli present on articles 11, 13, 15, 16, 22, 27, 28, 30, 31, 33, 34, 37, 43, 44, 47 and 49. Figure 12. Stephonyx laqueus ( Barnard, 1967 ) , male (19.6 mm), NSMT-Cr 22034, Sea of Okhotsk. (A) Head, lateral view; (B) right antenna 1, medial view; (C) peduncular articles 1–3, primary flagellum articles 1–3, and accessory flagellum of right antenna 1, medial view; (D) right antenna 2, medial view; (E) epistome and upper lip, lateral view; (F) lower lip (damaged and shrunk), ventral view; (G) left mandible, medial view; (H) incisor of right mandible, medial view; (I) maxilla 1, dorsal view; (J) outer plate of maxilla 1, dorsal view; (K) terminal article of palp of maxilla 1, dorsal view; (L) maxilla 2, dorsal view; (M) maxilliped (inner plate twisted outward), dorsal view; (N) inner plate of maxilliped, ventral view. Mouthpart bundle, subquadrate. Epistome and upper lip ( Figure 12E ) separated by notch, subequal. Mandible ( Figure 12G, H ) incisor smooth, left lacinia mobilis four-denticulate, right lacinia mobilis absent, accessory setal row present; molar setose, not triturative; palp attached midway, article 2 with setae along distal half of lateral margin, article 3 with setae along most of posterior margin, articles 1–3 in length ratio of 1.0: 1.8: 1.1. Lower lip ( Figure 12F ) outer lobe broad (shrunk by drying; before shrinkage, resembled Figure 14N ), lateral lobe long, inner lobe indistinct. Maxilla 1 ( Figure 12I–K ) with narrow inner plate, bearing four plumose setae apically; outer plate narrow, with 11 spine-teeth in a 7/4 crown arrangement; palp two-articulate, terminal article with six distal robust setae and slender seta. Maxilla 2 ( Figure 12L ) with inner plate shorter than outer plate, both setose. Maxilliped ( Figure 12M, N ) with subrectangular inner plate, bearing two nodular robust setae on inner distal corner and one on outer distal corner, oblique setal row well developed; outer plate large, subovate, with apical robust setae and plumose setae; palp four-articulate, dactylus with unguis. Figure 13. Stephonyx laqueus ( Barnard, 1967 ) , male (19.6 mm), NSMT-Cr 22034, Sea of Okhotsk. (A) Right gnathopod 1, medial view; (B) propodus and dactylus of right gnathopod 1, medial view; (C) distal parts of propodus and dactylus of right gnathopod 1, medial view; (D) right gnathopod 2, medial view; (E) propodus and dactylus of right gnathopod 2, medial Gnathopod 1 ( Figure 13A–C ) with reduced coxa, subquadrate; anterior margin of basis straight with slender setae, posterior margin bare; ischium elongate, 5.6 times width, 0.6 times basis; merus short; carpus linear, elongate, 6.6 times width and subequal to propodus in length, margins subparallel, anterior margin bare, straight; palmar margin of propodus serrate, slightly convex, distal corner with one lateral and one medial tooth; dactylus 0.3 times propodus, distally bifid with medial seta. Gnathopod 2 ( Figure 13D–F ) with large coxa, anterior margin convex, subequal to coxa 3; basis elongate, posterior margin weakly curved, anterior margin with setae; ischium elongate, 3.5 times width; posterior margin of merus rounded; carpus linear, elongate, 4.8 times width, margins subparallel; propodus oval, length 1.6 times width; palmar margin of propodus deeply concave; posterodistal corner 73 ◦ , with four medial stout setae; dactylus almost reaching palmar corner. Pereopod 3 ( Figure 13G, H ) subequal to pereopod 4, coxa subrectangular, propodus slender, dactylus simple, with posteroproximal crenulations. Pereopod 4 ( Figure 13I ) with well-developed posteroventral lobe of coxa; propodus slender, dactylus simple. Pereopod 5 ( Figure 13J ) with bilobed coxa, length 0.9 times width; posterior margins of basis and merus expanded. Pereopod 6 ( Figure 13K ) with subrectangular coxa, weakly bilobed; posteroventral lobe of basis well developed; posterior margin of merus broadly expanded. Pereopod 7 ( Figure 13L ) with subquadrate coxa; posterior margin of basis weakly convex, expanded, posteroventral lobe well developed; posterior margin of merus broadly expanded. Coxal gills on gnathopod 2 and pereopods 3–7. Coxal gills 2–6 with accessory lobe; gill 2 subovate, exceeding distal part of basis; gills 3–5 pyriform, exceeding distal part of basis; gill 6 horizontally long, reaching middle of basis; and gill 7 subquadrate, exceeding distal margin of coxa, but not reaching middle of basis. Pleopods 1–3 ( Figure 14A ) with paired retinacula ( Figure 14B ) and associated setae on inner distal corner of peduncle; inner basal margins of inner rami with 5–7 bifid plumose setae (clothes-pin setae) ( Figure 14C ); inner rami of pleopods 1–3 23-, 24- and 23-articulate, respectively; outer rami of pleopods 1–3 at least 14-, 27- and 26-articulate, respectively. view; (F) palmar margin of propodus and dactylus of right gnathopod 2, medial view; (G) right pereopod 3, medial view; (H) dactylus of right pereopod 3, medial view; (I–L) right pereopods 4–7, medial views. Figure 14. Stephonyx laqueus ( Barnard, 1967 ) , (A–J) male (19.6 mm), NSMT-Cr 22034; (K–Q) female (20.1 mm), NSMT-Cr 22033, Sea of Okhotsk. (A) Right pleopod 1, posterior view; (B) retinacula of right pleopod 1, posterior view; (C) distal end of bifid plumose setae (clothes-pin setae) of right pleopod 1, posterior view; (D–F) right epimeral plates 1–3, medial views; (G, H) Uropod 1 ( Figure 14G ) peduncle with medial and lateral robust setae; with outer ramus 0.9 times peduncle, bearing seven lateral and three medial marginal robust setae and terminal robust seta; inner ramus 1.1 times outer ramus, bearing five lateral and 11 medial marginal robust setae and terminal robust seta. Uropod 2 ( Figure14H ) peduncle with medial and lateral robust setae; with outer ramus 1.1 times peduncle, lateral and medial margins each with seven and one robust setae, with terminal robust seta; inner ramus 1.3 times outer ramus, lateral and medial margins each with five and 12 robust setae, with terminal seta. Uropod 3 ( Figure 14I ) with peduncle length 2.0 times width, laterodistal and mediodistal corner with robust setae; outer ramus 1.7 times peduncle, two-articulate, medial margin of proximal article with setae (broken); inner ramus subequal in length to outer ramus, medial margin with numerous plumose setae. Telson ( Figure 14J ) length 2.0 times width, cleft 89% of length, distal margin incised, with one penicillate seta and one robust seta on each lobe. Description of female Similar to male, except the following. Antenna 1 ( Figure 14K, L ) with primary flagellum 25-articulate, calceoli absent; callynophore small, 12 rows. Antenna 2 ( Figure 14M ) peduncular articles 4 and 5 lacking brush setae, flagellum 44-articulate, calceoli absent. Maxilla 1 ( Figure 14O, P ) with 10 spine-teeth in a 6/4 crown arrangement. Gnathopod 2 with posterodistal corner of propodus 80 ◦ . Uropod 3 ( Figure 14Q ) medial margin of proximal article with few plumose setae. Distribution San Benitos Islands, Baja California (J. L. Barnard, 1967 ), Kumano-nada (Northwest Pacific, Japan ) ( Sekiguchi and Yamaguchi 1983 ), and Sea of Okhotsk (this study); 330–1578 m . Remarks Stephonyx laqueus is morphologically similar to S. arabiensis in having article 1 of mandibular palp shorter than 0.5 times article 2, carpus of gnathopod 1 longer than 0.75 times propodus, concave palmar margin of gnathopod 2, and distal margin of telson incised. However, S. laqueus differs from S. arabiensis by the following features (features of S. arabiensis are shown in parentheses): lateral cephalic lobe rounded (pointed), palm of gnathopod 2 propodus more strongly concave (concave), dactylus of gnathopod 2 almost reaching (not reaching) distal corner of palmar margin, and anterior margin of coxa 4 weakly rounded (more rounded). The present specimens from Japan differ from the original description of S. laqueus by Barnard (1967) in the following point (information from the original description is right uropods 1 and 2, dorsal views; (I) right uropod 3, ventral view; (J) telson, dorsal view; (K) right antenna 1, medial view; (L) peduncular articles 1–3, primary flagellum articles 1–2, and accessory flagellum of right antenna 1, medial view; (M) right antenna 2, medial view; (N) lower lip, ventral view; (O) maxilla 1, dorsal view; (P) outer plate of maxilla 1, dorsal view; (Q) right uropod 3, ventral view. given in parentheses): the inner plate of maxilliped with three (two) nodular robust setae.