Scopelocheirus sossi, Zettler & Bastrop & Lowry, 2023

Zettler, Michael L., Bastrop, Ralf & Lowry, James K., 2023, Ten thousand kilometres away and still the same species? The mystery of identity of Scopelocheirus sp. (Amphipoda: Scopelocheiridae) from the South Atlantic, Records of the Australian Museum (Rec. Aust. Mus.) 75 (4), pp. 609-622 : 616-618

Scopelocheirus sossi sp. nov.

urn:lsid:zoobank.org:act:697B376F-15F7-4ACF-8BE9-110545096A4F

Figs 7–10

Holotype: Male , 6.6 mm, ZMB 34580 , Namibia, Namib Desert Coast, 25.0000°S 14.3775°E, water depth 130 m, amphipod trap, Stn. M 157_41, salinity at bottom 33.6 psu, temperature at bottom 10.5°C, oxygen 0.22 ml/l, collected 5 Sept 2019 . Paratypes: Paratype 1, male, 6.6 mm, ZMB 34581 , data same as holotype ; Paratype 2, female, 7.6 mm, ZMB 34582 , data same as holotype .

Other material examined. 18 individuals, ZMB 34583 , data same as holotype; 20 individuals, ZMB 34584 , Namibia, Namib Desert Coast , 25.0001°S 14.5611°E, water depth 107 m, amphipod trap, Stn. M 157_43, salinity at bottom 34.9 psu, temperature at bottom 10.7°C, oxygen 2.93 ml/l, collected 6 Sept 2019 .

Type locality. Namibia (Province Hardap) about 100 km west of Sossusvlei (Namib Desert) , 25.0000°S; 14.3775°E, in 130 m water depth.

Etymology. The name “sossi ” is the Latin genitive of “sossus” and is Nama for “no return” or “dead end” and refers to Sossusvlei, a salt and clay pan, located in the southern part of the Namib Desert, which is about 100 km east of the locus typicus.

Diagnosis. Lateral cephalic lobe weak triangulate. Eyes elongated oval. Slender shape of palpus of maxilla 1. Outer and inner plate of maxilla 2 subequal, both with feathered setae. Dorsal-anterior margin of segment 2 of mandible palp without setation. Coxae 1–4 lacking ventral setae. Basis of pereopod 5 wider than long with a brush of 8 or 9 feathered setae in the inner side. Clear longitudinal keel on basis of pereopod 5–7. Epimeral plate 2, ventral margin slightly concave with up to 6 setae anteroventrally, posteroventral corner rectangular. Uropods 1 and 2 sparsely spinose. Uropod 3, inner ramus reaching end of proximal article of outer ramus; inner ramus lined with plumose setae along medial margin.

Description. Based on male holotype, 6.6 mm. Head. Head lateral cephalic lobe weak triangulate, eyes elongated oval, of medium size. Antenna 1 short. Peduncle almost as long as head; peduncular article 1 very stout, as long as wide, dorsal margin with a row of 8 palm-like setae, ventral margin with a row of palm-like spines; peduncular articles 2 and 3 very short. Primary flagellum short, 11-articulate, 2 times as long as peduncle; flagellar article 1 large, callynophore well developed.Accessory flagellum 0.5 times as long as primary flagellum, 3-articulate; article 1 as long as primary flagellar article 1, calceoli absent. Antenna 2 longer than antenna 1, about half as long as body; peduncular articles 4 and 5 subequal in length; flagellum 28-articulate, calceoli absent. Labrum with epistome, slightly produced frontally, vaulted. Mandible incisor broad, cutting margin smooth and slightly convex, with blunt cusp on each side, 1 subacute tooth (left) and 3 acute teeth (right) on medial side. Lacinia mobilis on left, stemmed, expanded distally, with irregularly cusped blade. Palp attached midway, 3-articulate; article 2 longest, slightly swollen anteriorly, with oblique row of 15 setae distally; article 3 weakly falcate, 0.7 × as long as article 2, with 17 setae along distal ⅔ of posterior margin. Maxilla 1 inner plate narrowing distally, setose, with 10 plumose setae along medial margin and apex; outer plate with 10 toothed setae apically and with several setae submarginally; palp bi-articulate, distal article swollen distally, apical margin oblique, with 5 bi-dentate short setae and 1 mono-dentate elongate seta. Maxilla 2 each plate broad and subequal in length; inner plate with row of 19 plumose setae along distal half of medial and apical margins; outer plate with row of 14 plumose setae apically. Maxilliped inner plate with mediodistal row of plumose setae, apex with 3 nodular setae; outer plate well developed, half of palp length, lined with 12 nodular setae, several simple setae, palp 4-articulate, article 2 the longest, article 4 about ⅔ of article 3, with short apical seta.

Pereon. Gnathopod 1 of scopelocheirin form; coxal plate triangular; basis elongate, anterior and posterior margins straight, lined with 5–7 setae; ischium 0.4 × as long as basis; carpus elongate, 0.6 × as long as basis; merus half as long as ischium; carpus elongate, longer than ischium, 0.6 × basis; propodus subrectangular, slender, and longer than carpus, with dense tuft of stout setae covering the rudimentary dactylus. Gnathopod 2 slender; coxa subrectangular; basis elongate with parallel anterior and posterior margin lined with few long and short setae; ischium elongate, 0.7 × as long as basis; merus 0.5 × as long as ischium, round posteriorly, with many short setae and 1 bundle of long plumose setae; carpus as long as ischium, anterior margin swollen, with several clusters of short setae, long plumose setae at anterodistal and posterodistal corner reaching mid-propodus; propodus oval, 0.6 × as long as carpus, with clusters of small setae and 6 bundles of plumose setae distally; dactylus fitting palm, minutely chelate. Pereopod 3 stout; coxa subrectangular, similar to coxa 2, slightly curved; basis rectangular, elongate with few short and three longer setae; ischium 0.3 × as long as basis, anterior lobe weak, several long setae on posterior margin; merus expanded anteriorly, half as long as basis, several long setae on posterior margin, anterodistal corner weakly produced with bundle of setae; carpus slender, 0.8 × as long as merus, with simple and robust setae on posterior margin; propodus 2 × as long as carpus, lined with robust setae on posterior margin and few longer setae, with pair of locking setae posterodistally; dactylus falcate, 0.3 × as long as propodus. Pereopod 4 coxa 4 much broader than other coxae, with well-developed posteroventral lobe, other articles similar to pereopod 3, though propodus shorter. Pereopod 5 coxa large, rounded; basis with a weak longitudinal keel, broadly expanded, with a row of single robust spines along anterior margin, with a brush of 8 long plumose setae in middle of inner side; ischium 0.3 × as long as basis with few long and short setae on anterior margin, merus 2 × as long as ischium with several robust and some longer setae anteriorly; posterior expansion ending in lobe with row of 9 long setae and 1 apical spine; carpus 0.8 × as long as merus lined with clusters of spines anteriorly; propodus 2 × as long as carpus, with 4 clusters of paired spines along anterior margin and 1 posterodistal seta. Pereopod 6 longer and more slender than pereopod 5; coxa subrectangular, smaller than coxa 5, with 7 plumose setae anteriorly, and 6 plumose setae posteroventrally; basis ovoid, 1.7 × as long as wide, with weak longitudinal keel, anterior margin rounded proximally and straight distally, bearing short robust setae, posterior margin broadly expanded, smooth, weakly crenulate, bearing 10 small setae, posterodistal end reaching almost the end of ischium; ischium short half as long as merus, l with 4 pairs of robust spines anteriorly; merus half as long as basis, slightly expanded posteriorly with several spines along the margins; carpus rectangular, elongate, 1.2 × as long as merus, with 4 pairs of spines anteriorly and 2 setae posterodistally; propodus linear, slightly longer than carpus, with single and paired robust setae on anterior margin and 4 simple long setae on posterior margin, posterodistal edge with 1 long spine; dactylus falcate, 0.2 × as long as propodus. Pereopod 7 coxa rhomboid, with 3 plumose setae anteriorly; basis 1.4 times as long as wide, with weak longitudinal keel, anterior margin weakly concave armed with several small spines, posterior margin convex and crenulate with several small setae, posterodistal lobe obtuse, nearly as long as ischium; merus slender other articles similar to pereopod 6.

Pleon. Epimeron 1 rounded, obtuse-angled anteroventrally with 1 spine. Epimeron 2 subquadrate, concave ventrally, posterior margin crenulate, 6 spines anteroventrally. Epimeron 3 rounded, posterior margin slightly crenulate, 6 spines on ventral margin. Urosomite 1 with deep dorsal depression and mid-dorsal carina. Uropod 1 peduncle longer than rami, peduncle with 6 robust setae on dorsolateral margin and 5 robust setae on dorsomedial margin; outer ramus with 6 lateral robust setae and 1 apical spine; inner ramus as long as outer ramus, with 2 medial and 2 lateral robust setae and one apical spine. Uropod 2 as long as uropod 1; peduncle with 3 robust setae medially and 6 robust setae laterally on each dorsal margin; outer ramus with 5 lateral robust setae only and 1 apical spine; inner ramus as long as outer ramus, with 3 lateral and 2 medial robust setae and 1 apical spine. Uropod 3 0.8 × as long as uropod 2; peduncle with 1 pair of robust setae distally on each side and 2 long setae medially; outer ramus bi-articulate, basal article with 3 lateral setae and 2 terminal setae; inner ramus 0.8 × as long as outer ramus, reaching distal end of proximal article of outer ramus, with 3 lateral setae and row of plumose setae along medial margin. Telson longer than broad, cleft about 80%, each lobe with apical notch bearing 1 robust and 1 slender seta apically, with 2 or 3 robust setae and 1 pair of sensory setae dorsolaterally.

Female. (Paratype 2). Females in general very similar to males but slightly larger. Antenna 1 slightly shorter than in male; peduncular article 1 more slender; primary flagellum 8-articulate. Antenna 2 shorter than in male, reaching one-third of body length; flagellum 24-articulate. Oostegites present on pereopods 2–5.

Habitat. This new species occurred in water depths between 107 and 130 m on muddy sediments. The salinity ranged between 33.6 and 34.9 psu, the oxygen content in bottom water varied between 0.22 and 2.93 ml/l. The temperatures were about 10°C.

Distribution. Currently known only from the coast of Namibia.

Remarks. Scopelocheirus sossi sp. nov. can be separated from the Kattegat entity, herein identified as S. hopei , by the following characters ( S. hopei in brackets). Eyes small, 0.4 × height of head (larger, 0.5 × height of head); palp of maxilla 1 slender (broader); pereopod 5 basis with 8 or 9 plumose setae on medial surface (4 or 5); pereopod 5 merus expanded posterodistally (expanded along whole posterior margin); pereopods 5–7 basis with longitudinal keel as seen in Aroui minusetosus Jung, Coleman & Yoon, 2017 (keel absent); epimeron 3 ventral margin with six spines (nine spines); telson length 2 × width with 2 or 3 pairs of dorsal spines (length 2.2 × width with 1 pair of dorsal spines); body uniformly yellowish without pigment spots (body densely mottled with yellowish-orange pigment spots (in life sometimes with numerous brown spots)).

Figures

Figure 7. Habitus photograph of Scopelocheirus sossi sp. nov., female, 6.2 mm, Namibia, Stn. M157_41.

Figure 8. Scopelocheirus sossi sp. nov., holotype, male, 6.6 mm, Namibia, habitus, Stn. M157_41.

Figure 9. Scopelocheirus sossi sp. nov., holotype, male, 6.6 mm, Namibia, Stn. M157_41.

Figure 10. Scopelocheirus sossi sp. nov., holotype, male, 6.6 mm, Namibia, scale bar 200 µm, Stn. M157_41.