Antarctophiline abyssalis Peralta-Serrano, Schrödl, Wilson & Moles, 2025, sp. nov.

Antarctophiline abyssalis sp. nov. Diagnosis Body oval, large, arched sagittally, white nacreous coloured. Cephalic shield sub-rectangular. Shell internal, ovate-subquadrate, slightly angled dorsally, wide dorsoventrally. Radular formula 15 × 2.1.0.1.2. Gizzard plates (3) elongated, oval, ventral plate smaller than dorsal ones; internal surface highly chitinous, convex, holes or slits absent; external surface flattened, with concentric amber and dark brown bands. ZooBank registration urn:lsid:zoobank.org:act:2B7C5D1E-C187-47CE-8897-250E481- 2071F. Etymology The species’ name derives from its depth distribution encompassing the abyssal plain from ~ 3000 to 4550 m depth. Type locality Transition Weddell Sea to south of South Sandwich Islands, 2892.8–4547.6 m depth. Material examined Transition Weddell Sea to south of South Sandwich Islands, St. PS 61/1384, 62 ○ 57 ′ 48 ′′ S, 27 ○ 52 ′ 8.4 ′′ W, 4547.6 m depth: 1 specimen, ZSM20021046 (holotype; 16 March 2002), COI barcode MN486283, L = 27 mm, W = 10 mm. North Elephant Island, St. PS 61/046-7, 60 ○ 39 ′ 11.4 ′′ S, 53 ○ 56 ′ 51 ′′ W, 2892.8 m depth: 1 specimen, sequenced, ZSM20021211 (paratype; 30 January 2002), COI barcode MN486284, L = 5 mm, W = 2 mm. Northwest Bouvet Island, South Atlantic Ocean, St. PS 71/013-15, 52 ○ 2 ′ 31.8 ′′ S, 0 ○ 0 ′ 36 ′′ E, 2996 m depth: 2 specimens, 2 sequenced, ZSM20081179 (paratypes; 6 December 2007), COI barcode MN486285, L = 10 mm, W = 5 mm, COI barcode MN486286, L = 8 mm, W = 3 mm; St. PS 79/081-18, 52 ○ 21 ′′ S, 10 ○ 1 ′ 28 ′′ E, 3705–3757 m depth: 1 specimen, ZSM20130151 (paratype; 20 January 2012), COI barcode MN486287, L = 16 mm, W = 5 mm; PS79/081-17, 52 ○ 11 ′′ S, 10 ○ 43 ′′ E, 3743–3763 m depth: 1 specimen, dissected, ZSM20130153 (paratype; 20 January 2012), COI barcode MN486288, L = 27 mm, W = 11 mm. External morphology (Fig. 6a) Maximum L = 27 mm, W = 11 mm. Body oval, large, arched sagittally. Shell slightly wide, white nacreous coloured; surrounded by translucent white thin mantle. Cephalic shield sub-rectangular, representing 45% body extension, slightly over shell; posteriorly slightly bilobed. Parapodia triangular, extended over shell. Foot smooth, extending from mouth approximately three-fifths of the animal. Shell (Fig. 6b) Maximum L = 12.6 mm, W = 8.6. Internal, ovate-subrectangular, white, thin, slightly angled dorsally, wide dorsoventrally. Periostracum thin, pellucid. Aperture almost representing full extension of shell. Columellar wall concave. Parietal callus thin; outer lip directed towards body whorl, extending downwards. Body whorl wide. Apex bulky, umbilicated, sunken, left-sided. Growth lines marked. Radula (Fig. 6c) Radular formula 15 × 2.1.0.1.2. Rachidian not detected. Lateral teeth hook-shaped, inner lateral thick, with broad base, tip rounded or pointed, inner edge with very faint denticulation. Outer lateral teeth hook-shaped, with broad base, tip rounded or pointed. Digestive tract (Fig. 6e) Buccal mass highly muscular. Salivary glands long, connected ventrally, entering pharynx from dorsal end, extending under pharynx, going up over crop to beginning of gizzard. Crop globose, saccular, thin walled. Gizzard elongated, surrounded by circular muscle fibres. Gizzard plates (3; maximum L = 1.5 mm, W = 0.8 mm), elongated, oval, ventral plate smaller than dorsal ones; internal surface highly chitinous, convex, translucid, holes or slits absent; external surface flattened, with concentric amber and dark brown bands (Fig. 6e,f); spines present in gizzard (Fig. 6d). Male reproductive system (Fig. 6g,h) Penial sheath short, pyriform. Penial papilla small, ~ 4 mm in length. Ejaculatory duct surrounded by musculature tissue. Prostate granulose, saccular, shorter than penial sheath, displayed attached to seminal vesicle. Seminal vesicle saccular, slightly smaller than prostate, containing autosperm. Ecology Found in abyssal plains from 2892.8 to 4547.6 m depth. Sponge spicules and foraminifera were found in the gut contents of the single specimen studied (Fig. 5d–f). Distribution Known from the South Atlantic Antarctic Ridge, from the vicinities of Bouvet Island to Elephant Island. Remarks The new species is differentiated from its counterparts (i.e. A. alata, A. amundseni, A. apertissima, A. easmithi, A. falklandica, A. gibba, A. malaquiasi sp. nov.) by the larger size and wider shell. The shell has a large columellar callus and presents a greater length/width ratio and larger body compared to the other species. In addition, the dark brown, highly chitinous, small gizzard plates, pronouncedly convex internally and flattened externally, are characteristic of this species. The bathymetric range of A. abyssalis sp. nov. encompasses bathyal and abyssal depths in the South Atlantic Antarctic Ridge, where no previous records of any other species are found. The most closely related species is A. amundseni, known from 196 to 1048 m depth in the Weddell Sea.