Sophrosyne antarctica Ren in Ren & Huang, 1991: 249, 308, fig. 39. — De Broyer & Jazdzewski, 1993: 15, 75. — De Broyer et al., 2007: 159.
Type locality. South Shetland Islands, Southern Ocean (62°50.6'S 60°20.5'W), 860 m.
Diagnostic description. Head lateral cephalic lobe small, narrowly rounded; eyes apparently absent. Antenna 1 peduncular article 1 short, length 1.3 x breadth; accessory flagellum long, 0.5 x primary flagellum, article 1 long, 2.6 x article 2; flagellum 7-articulate, without callynophore. Antenna 2 peduncular article 3 0.5 x article 4; flagellum 6-articulate. Mandible incisors with straight margins; palp article 2 slender, 1.1 x article 3, without A2-setae, without D2-setae, article 3 length 4.8 x breadth, without D3-setae, with 4 apical E3- setae. Maxilla 1 outer plate with setal-teeth in a 2/1 arrangement . Maxilla 2 inner plate narrow, outer plate broader; inner plate length 0.56 x outer plate. Maxilliped inner plate subrectangular, without apical nodular robust setae; outer plate submarginal setae absent; palp article 2 slender, length 2.4 x breadth, 1.1 x article 3, article 3 slender, length 2.4 x breadth, dactylus with unguis absent. Gnathopod 1 basis length x breadth unknown, anterior margin with slender setae; ischium length 1 x breadth; merus, posterior margin with a few slender setae; carpus length 0.5 x propodus; propodus length 1.7 x breadth, posterior margin subtly sinusoidal, with simple, slender setae, palm margin straight, posterodistal corner with produced subacute spine bearing vestigial seta. Gnathopod 2 minutely subchelate; ischium length 3 x breadth; carpus long, length 3.5 x breadth, posterior margin straight; propodus subrectangular, long, length 2.5 x breadth; palm slightly acute, with concave, smooth margin. Pereopod 3 merus weakly expanded anteriorly. Pereopod 4 merus not expanded anteriorly. Pereopod 5 basis moderately expanded posteriorly; merus slightly expanded posteriorly. Pereopod 6 coxa small, not lobate posteriorly; merus expanded posteriorly. Pereopod 7 basis posterior margin slightly rounded, minutely crenate, posteroventral margin rounded, posteroventral lobe not extending beyond ischium; merus slightly expanded posteriorly; propodus with setae along anterior margin. Epimeron 3 posterior margin with strong upturned spine above rounded posteroventral corner. Urosomite 1 with anterodorsal notch and rounded boss, without lateral flange. Uropod 1 outer ramus slightly longer than inner ramus. Uropod 2 rami subequal in length; rami without robust setae. Uropod 3 peduncle length 1.4 x breadth; rami subequal in length. Telson longer than broad, length 1.2 x breadth, moderately cleft (62%), distal margins rounded, with 1 apical slender seta on each lobe.
Remarks. Sophrosyne antarctica shares with S. californica and S. cantractia a vestigial seta on the posterodistal corner of the gnathopod 2 propodus and a curved posteroventral corner with strong upturned tooth on epimeron 3. Sophrosyne antarctica differs from S. californica in the lack of A- and D-setae on the mandibular palp, in the arrangement of setal-teeth on the outer plate of maxilla 1 and in the presence of slender setae along the posterior margin of the propodus of gnathopod 1. It differs from the other Antarctic species, S. cantractia, in the lack of A- and D-setae on the mandibular palp, in the arrangement of setal-teeth on the outer plate of maxilla 1, in the slender maxillipedal palp article 2 and in the scarcity of slender setae along the posterior margin of the merus of gnathopod 1.
Distribution. South Shetland Islands and Palmer Archipelago, Antarctica in 180–860 m depth.