Stenopontius alatus, Lee, 2025

Stenopontius alatus View in CoL n. sp. ( Figs. 19 View Fig , 20 View Fig )

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5CDF-407B-A8FE-BFAEDC3AD997

Type material. Holotype (♀, dissected and mounted on a slide; MABIK CR00257790 ) from washings of dredged invertebrates collected from the Korea Strait (33°13 ʹ 39.4 ʺ N, 126°33 ʹ 48.2 ʺ E), at a depth of 127 m, collected by Jimin Lee, on 17 March 2024. The holotype has been deposited in the National Marine Biological Institute of Korea ( MABIK), Seocheon. GoogleMaps

Etymology. The name is derived from the Latin alat (= winged), referring to the wing-like lateral expansions of the genital double-somite and first abdominal somite.

Female. Body ( Fig. 19A View Fig ) small, narrow, slightly dorsoventrally depressed. Body length 455 μm. Prosome with parallel lateral margins, 239 × 155 μm. Cephalothorax 134 μm long, wider than long. Fourth pedigerous somite with irregularly curved posterior margin. Urosome ( Fig. 19B View Fig ) 5-segmented. Fifth pedigerous somite narrow, 60 μm wide. Genital double-somite 85 × 126 μm, peculiarly consisting of narrow anterior 40% (68 μm wide at this part) and greatly broadened, wing-like posterior 60%, with produced, angular posterolateral corners; genital apertures positioned dorsolaterally at posterior region of narrow anterior part. First abdominal somite 34 × 85 μm, with wing-like, posterolateral expansions. Second abdominal somite 22 × 56 μm, posterolaterally expanded. Anal somite ( Fig. 19C View Fig ) 27 × 43 μm, with angular posterolateral corners and large anal operculum; anal operculum covering proximal part of caudal rami. Caudal ramus ( Fig. 19C View Fig ) 1.56 times longer than wide (25 × 16 μm), broadening distally, with pointed posterolateral and posteromedial corners, armed with 6 short setae; dorsal seta (seta VII) naked, other setae pinnate.

Rostrum absent. Antennule ( Fig. 19D View Fig ) 12-segmented; armature of proximal segments uncertain, due to damage of setae; armature of distal 3 segments 3, 1, and 10 + aesthetasc; terminal segment longest; ninth segment distinctly narrower than other segments. Antenna ( Fig. 19E View Fig ) consisting of 4 segments and terminal claw; coxa short, unarmed; basis 33 μm long; exopod represented by 2 subequal, naked setae located at about distal third of outer margin of basis; first endopodal segment (third segment) unarmed, 30 μm long; second endopodal segment 12 μm long, bearing 3 small setae; terminal claw smooth, strongly curved at distal 80% region, with acutely pointed distal tip.

Oral siphon ( Fig. 19F View Fig ) 98 × 34 μm, gradually narrowing distally, with truncate distal apex. Mandible ( Fig. 19G View Fig ) represented by straight, needle-like stylet of 84 μm long; palp absent. Maxillule ( Fig. 19G View Fig ) bilobed; small outer lobe 10 μm long, tipped with 2 equal, naked setae, both of them 38 μm long; inner lobe about 30 μm long, tipped with 3 subequal, naked setae, longest middle one of them 59 μm long. Maxilla ( Fig. 19H View Fig ) 2-segmented; proximal segment (syncoxa) 30 μm long, smooth; distal segment (basis) 60 μm long, bearing spinules and setules on convex margin. Maxilliped ( Fig. 19I View Fig ) 5-segmented; armature formula 0, 0, 0, 2, and 1 + claw; lengths of second segment (basis) to terminal claw 42, 9, 30, 24, and 32 μm, respectively.

Legs 1-4 ( Fig. 20A- D View Fig ) with 3-segmented rami; coxa lacking inner seta. Intercoxal plate of legs 2-4 sparsely covered with spinules. Inner margin of basis of legs 1-4 protruded, that of legs 1-3 with fine spinules. First exopodal segment of leg 1 lacking inner seta. Outer and distal setae on third endopodal segment of leg 1 naked. Inner seta on first exopodal segment of legs 2-4 short. Second endopodal segment of legs 1-4 with bicuspid outer distal corner. Armature formula for legs 1-4 as follows:

Coxa Basis Exopod Endopod Leg 1 0-0 1-I I-0; I-1; II, 2, 3 0-1; 0-2; 1, 2, 3 Leg 2 0-0 1-0 I-1; I-1; III, I, 5 0-1; 0-2; 1, 2, 3 Leg 3 0-0 1-0 I-1; I-1; III, I, 5 0-1; 0-2; 1, I, 3 Leg 4 0-0 1-0 I-1; I-1; III, I, 5 0-1; 0-2; 0, I, 2

Leg 5 ( Fig. 19J View Fig ) consisting of protopod and exopod; protopod distinctly articulated from somite, bearing 1 pinnate seta on outer margin; exopodal segment oval, 1.42 times longer than wide (51 × 36 μm), bearing 3 small, naked setae on distal margin; lengths of these setae 25, 9, and 14 μm, respectively, from inner to outer. Leg 6 ( Fig. 19K View Fig ) represented by 1 seta and 1 spinules on genital operculum.

Male. Unknown.

Remarks. The new species is clearly distinguishable from other species of Stenopontius by the unique shape of the female urosome, featuring wing-like lateral expansions on the genital double-somite and the first abdominal somite. These are distinctive key characteristics of the new species.

The armature condition (two spines plus five setae) on the third exopodal segment of leg 1 is also unique within the genus, as it differs from the condition present in S. boxshalli and S. humesi or compared to three spines plus five setae in S. parvus and S. brevicauda n. sp., or three spines plus four setae in S. spinulatus Kim, 2010 (Marnane, 1967; Boxshall, 1990; Malt, 1991; Kim, 2010).