Stephonyx biscayensis ( Chevreux, 1908 )

Narahara, Yukiko, Tomikawa, Ko & Torigoe, Kenji, 2012, Four species of the genus Stephonyx (Crustacea: Amphipoda: Uristidae) from Japan, with description of a new species, Journal of Natural History (J. Nat. Hist.) 46 (23 - 24), pp. 1477-1507 : 1486-1493

publication ID	https://doi.org/ 10.1080/00222933.2012.675598
publication LSID	lsid:zoobank.org:pub:B4D66BC0-1866-4F68-95C0-2A1584B6141B
persistent identifier	https://treatment.plazi.org/id/3F55985F-FFB9-FF93-DDD1-AD4F2603FCB0
treatment provided by	Felipe
scientific name	Stephonyx biscayensis ( Chevreux, 1908 )
status

Treatment

Stephonyx biscayensis ( Chevreux, 1908) View in CoL

(Japanese name: Biskê-tsumamisokoebi, new)

( Figures 7–11 View Figure 7 View Figure 8 View Figure 9 View Figure 10 View Figure 11 )

Euonyx biscayensis Chevreux, 1908: 1 View in CoL , fig. 1;? Barnard, 1916: 110; Stephensen, 1923: 42;? Schellenberg, 1926: 200; Chevreux: 1927: 47, 1935: 7, pl. 5, fig. 2;? Barnard, 1961: 34, fig. 4;? Griffiths, 1975: 144;? Ledoyer, 1986: 748, fig. 289.

Stephonyx biscayensis: Lowry and Stoddart, 1989: 522 View in CoL , figs 23; Palerund and Vader, 1991: 43 (list); Poupin, 1994: 16 (list);? Lowry and Stoddart, 1997: 129, figure 63; Diffenthal and Horton, 2007: 39 (key); Senna and Serejo, 2007: 13 (key).

Stephonyx sp. :? Paulmier, 1993: 29, pl. 34, fig. 1 (list).

Material examined

NSMT-Cr 22021–22025, five males (22.1–27.4 mm), NSMT-Cr 22026–22030, five females (21.4–27.4 mm), East China Sea, 28 ◦ 29.5 ′ N, 127 ◦ 59.2 ′ E, baited trap, 1073–1080 m, bottom at 10:08 on 29 July 2010, R / V GoogleMaps Soyo-maru , Soyo-2010, St-trap 7 (Okinawa Trough), 30 July 2010, coll. K. Kakui.

NSMT-Cr 22031, one female (23.9 mm), NSMT-Cr 22032, one male juvenile (17.1 mm), off Aguni-jima Island (East China Sea), 26 ◦ 48 ′ N, 127 ◦ 26 ′ E, baited trap, 856–910 m, bottom at around 13:00 on 13 September 2010 GoogleMaps , Kohuku-maru , 14 September 2010, coll. Atsushi Kaneko.

Description of male

Head ( Figure 7A View Figure 7 ) deeper than long, lateral cephalic lobe rounded; rostrum absent; eyes L-shaped. Epimeral plates 1–3 ( Figure 9G–I View Figure 9 ) 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 7B, C View Figure 7 ) 0.2 times body length, peduncular articles 1–3 length ratio of 1.0: 0.3: 0.4; accessory flagellum 8–10-articulate; primary flagellum 21–26-articulate, calceoli present on the 5–22 articles; callynophore well-developed, 39–46 rows, two fields. Antenna 2 ( Figure 7D View Figure 7 ) 1.7–2.0 times antenna 1; anterior margins of peduncular articles 4 and 5 with brush setae, peduncular articles 4 and 5 not swollen; flagellum 44–53-articulate; calceoli present on the 1–49 articles.

Mouthpart bundle, subquadrate. Epistome and upper lip ( Figure 7E View Figure 7 ) separated by notch, subequal. Mandible ( Figure 7G, H View Figure 7 ) incisor smooth, with 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: 2.6–3.0: 2.0–2.3. Lower lip ( Figure 7F View Figure 7 ) with broad outer lobe, lateral lobe long, inner lobe indistinct. Maxilla 1 ( Figure 7I–K View Figure 7 ) with ovate inner plate, bearing three plumose setae apically; outer plate narrow, with 11 spine-teeth in a 7/4 crown arrangement; palp two-articulate, terminal article with six to eight robust setae and one or two slender setae. Maxilla 2 ( Figure 7L View Figure 7 ) with inner plate slender and shorter than outer plate, both setose. Maxilliped ( Figure 7M, N View Figure 7 ) with subrectangular inner plate, bearing two or three 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.

Gnathopod 1 ( Figure 8A–C View Figure 8 ) with reduced coxa, subquadrate; anterior margin of basis straight with slender setae, posterior margin with minute setae; ischium elongate; merus short; carpus linear, 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 8D–F View Figure 8 ) with large coxa, subequal to coxa 3, anterior margin convex; basis elongate, posterior margin weakly curved, anterior margin with minute setae; ischium elongate; posterior margin of merus rounded; carpus linear, elongate, margins subparallel; propodus oval, length 1.7–2.0 times width; palmar margin of propodus slightly convex, oblique, with medial stout setae; dactylus not reaching palmar corner. Pereopod 3 ( Figure 8G, H View Figure 8 ) subequal to pereopod 4, coxa subrectangular, propodus slender, dactylus simple, with posteroproximal crenulations. Pereopod 4 ( Figure 8I View Figure 8 ) with well-developed posteroventral lobe of coxa, propodus slender, dactylus simple. Pereopod 5 ( Figure 9A View Figure 9 ) with bilobed coxa, length slightly shorter than wide; posterior margin of basis with posteroventral lobe, posterior margins of basis and merus expanded. Pereopod 6 ( Figure 9B View Figure 9 ) with subrectangular coxa, weakly bilobed; posterior margin of basis expanded, posteroventral lobe developed; posterior margin of merus broadly expanded. Pereopod 7 ( Figure 9C View Figure 9 ) with subquadrate coxa; posterior margin of basis expanded, weakly convex, posteroventral lobe 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 9D View Figure 9 ) with paired retinacula ( Figure 9E View Figure 9 ) and associated setae on inner distal corners of peduncles; inner basal margins of inner rami with 6–11 bifid plumose setae (clothes-pin setae) ( Figure 9F View Figure 9 ); inner rami of pleopods 1–3 24–26-, 25–28- and 23–27-articulate, respectively; outer rami of pleopods 1–3 27–31-, 28–30- and 27–30-articulate, respectively.

Uropod 1 ( Figure 10A View Figure 10 ) peduncle with medial and lateral robust setae; with outer ramus 0.8–0.9 times peduncle, bearing nine to eleven lateral and four to six medial marginal robust setae and terminal robust seta; inner ramus 1.1 times outer ramus, bearing four to seven lateral and 12–15 medial marginal robust setae and terminal robust seta. Uropod 2 ( Figure 10B View Figure 10 ) peduncle with medial and lateral robust setae; with outer ramus 0.9–1.0 times peduncle, lateral and medial margins each with eight to ten and three to four robust setae, with terminal robust seta; inner ramus 1.2–1.3 times outer ramus, lateral and medial margins each with three to five and 14–17, with terminal robust seta. Uropod 3 ( Figure 10C View Figure 10 ) laterodistal and mediodistal corners of peduncle with robust setae; outer ramus two-articulate, medial margin of proximal article with plumose setae; inner ramus subequal in length to proximal article of outer ramus, medial margin with numerous plumose setae.

Telson ( Figure 10D, E View Figure 10 ) cleft for about 90% of length, dorsal surface with ( Figure 10D View Figure 10 ) or without ( Figure 10E View Figure 10 ) robust setae, distal margin incised, with one or two penicillate setae and two or three robust setae on each lobe.

Description of female

Similar to male except the following. Antenna 1 ( Figure 11A, B View Figure 11 ) with primary flagellum 22–26-articulate, calceoli absent; callynophore much smaller, 26–28 rows. Antenna 2 ( Figure 11C View Figure 11 ) 1.5–1.7 times antenna 1, flagellum 37–41-articulate, calceoli absent. Medial margin of uropod 3 ( Figure 11E View Figure 11 ) outer ramus has fewer plumose setae. Oostegites ( Figure 11D View Figure 11 ) on gnathopod 2 and pereopods 3–5, baculiform, margins irregular, without setae.

Distribution

The Bay of Biscay ( Chevreux 1908), North Atlantic Ocean ( Stephensen 1923; Chevreux 1927; Lowry and Stoddart 1989; Palerud and Vader 1991), South Atlantic Ocean ( Barnard 1916; Schellenberg 1926; Griffiths 1975), Indian Ocean ( Barnard 1961; Ledoyer 1986), Caribbean Sea ( Paulmier 1993; Poupin 1994; Lowry and Stoddart 1997), and East China Sea (this study); 494–1510 m.

Remarks

Stephonyx biscayensis View in CoL is closely similar to S. mytilus View in CoL in having a rounded lateral cephalic lobe, 11 spine-teeth on the outer plate of maxilla 1, slightly convex palmar margin of gnathopod 2, and dactylus of gnathopod 2 not reaching distal corner of palmar margin. However, this species is distinguished from S. mytilus View in CoL by the longer propodus of gnathopod 2 (1.7–2.0 times width in S. biscayensis View in CoL vs 1.4–1.6 times width in S. mytilus View in CoL ) and length of inner ramus of uropod 3 (as long as proximal article of outer ramus in S. biscayensis View in CoL vs as long as outer ramus in S. mytilus View in CoL ). Barnard (1961) described S. biscayensis View in CoL based on two specimens collected from the Indian Ocean, off Kenya. He distinguished S. biscayensis View in CoL from S. mytilus View in CoL by the rounded, posteroventral corner of epimeral plate 2 (pointed in S. mytilus View in CoL ). Though the epimeral plate 2 was not described in the original description of S. biscayensis View in CoL by Chevreux (1908), no other description or illustration of this species shows a rounded posteroventral corner of epimeral plate 2 ( Barnard 1916; Ledoyer 1986; Lowry and Stoddart 1989). Lowry and Stoddart (1989) and Diffenthal and Horton (2007) regarded Barnard’s (1961) S. biscayensis View in CoL as an undescribed species of Stephonyx View in CoL and we agree with their opinions.