Retusa sulcata (Watson, 1883)

Valdés, Ángel, 2008, Deep-sea “ cephalaspidean ” heterobranchs (Gastropoda) from the tropical southwest Pacific, Mémoires du Muséum national d'Histoire naturelle 196, pp. 587-792 : 730-731

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scientific name	Retusa sulcata (Watson, 1883)
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Retusa sulcata (Watson, 1883) View in CoL

Figs 71C, D, 72, 73A

Cylichna (Volvulella) sulcata Watson, 1883: 326 .

TYPE MATERIAL. — 3 syntypes BMNH 1887.2.9.2284-6 .

TYPE LOCALITY. — Torres Strait , north Australia, 6-20 m [Challenger]; Wednesday Island, Torres Strait, north Australia, 10°30’S, 142°18’E, 15 m [Challenger: stn 186] GoogleMaps .

MATERIAL EXAMINED. — Coral Sea. MUSORSTOM 5: stn 340, 167°10’E, 675-680 m, 1 dd; stn DW 56 , 23°35’S, 167°12’E, Chesterfield Islands , 19°49’S, 158°41’E, 675-680 m, 2 dd; stn 695-705 m, 1 dd GoogleMaps .

380, 19°38’S, 158°44’E, 555-570 m, 3 dd. Loyalty Ridge. MUSORSTOM 6: stn DW 468, 21°06’S, 167°33’E, North of New Caledonia. MUSORSTOM 4: stn DW 149, 19°08’S, 600 m, 1 dd.

163°23’E, 155 m, 11 dd, 1 lv destroyed to dissect the gizzard pla- Fiji. SUVA 2: stn DW 04, Rewa roads, Viti Levu, 18°12’S, 178°35’E, tes (Fig. 73A); stn DW 150, 19°07’S, 163°22’E, 110 m, 15 dd, 1 100-122 m, 1 dd (Figs 71C, D).

lv; stn DW 151, 19°07’S, 163°22’E, 200 m, 13 dd; stn DW 159, Tonga. BORDAU 2: stn DW 1549, S of Nomuka Islands, 20°38’S, 18°46’S, 163°16’E, 585 m, 1 dd; stn CC 174, 19°00’S, 163°18’E, 175°00’W, 500 m, 2 dd.

365 m, 1 dd. — BATHUS 4 : stn DW 894 , Passe de Poum , 20°16’S, Vanuatu. MUSORSTOM 8: stn CP 1131-1132, 15°38’S, 167°03- 163°52’E, 245-268 m, 1 dd; stn DW 914 , Grand Passage, 18°49’S, 04’E, 140-182 m, 5 dd GoogleMaps .

163°15’E, 600-616 m, 25 dd; stn DW 917 , 18°47’S, 163°14’E, Wallis and Futuna. MUSORSTOM 7: stn DW 494 , Futuna Is- 397-400 m, 2 dd. land, 14°19’S, 178°03’W, 100-110 m, 1 dd; stn DW 523 , Wallis New Caledonia proper. BIOCAL: stn DW 77 , 22°15’S, 167°15’E, Island, 13°12’S, 176°16’W, 455-515 m, 3 dd; stn DW 529 , Banc 440 m, 9 dd GoogleMaps . — BATHUS 4 : stn DW 887 , Passe de Duroc , 21°07’S, Waterwitch, 12°31’S, 176°40’W, 500 m, 2 dd; stn DW 540 , Banc 164°28’E, 320-344 m, 1 dd. Combe, 12°27’S, 177°28’W, 600 m, 1 dd; stn DW 555 , Banc Tus- Norfolk Ridge. SMIB 3 : stn DW 21 , 22°59’S, 167°19’E, 525 carora, 11°47’S, 178°19’W, 540-542 m, 1 dd; stn DW 569 , Banc m, 1 dd; stn DW 22 , 23°03’S, 167°19’E, 503 m, 2 dd GoogleMaps . — SMIB Waterwitch, 12°30’S, 176°51’W, 300-305 m, 1 dd; stn DW 585 , 5 : stn DW 101 , Banc Aztèque, 23°21’S, 168°05’E, 270 m, 1 Wallis Island, 13°10’S, 176°13’W, 415-475 m, 2 dd; stn DW 594 , dd GoogleMaps . — BATHUS 3 : stn DW 824 , Banc Jumeau Ouest, 23°19’S, Banc Field, 12°31’S, 174°20’W, 495-505 m, 1 dd; stn DW 601 , 168°00’E, 601-608 m, 1 dd GoogleMaps . — VAUBAN: stn 22, 22°59’S, Wallis Island, 13°19’S, 176°17’W, 350 m, 18 dd; stn DW 604 , 167°17’E, 540-545 m, 1 dd GoogleMaps . — BIOCAL: stn DW 33 , 23°10’S, 13°21’S, 176°08’W, 415-420 m, 7 dd GoogleMaps .

DISTRIBUTION. — Originally described from the Torres Strait , Australia, in 6-20 m (Watson, 1883). Records herein from the Coral Sea, Fiji, New Caledonia, Tonga, Vanuatu and Wallis and Futuna (Fig. 72), in 110-695 m, live in 110- 155 m.

DESCRIPTION. — Shell morphology. Length 6 mm, width 2 mm (largest specimen examined). Shell fragile, elongate, with nearly parallel sides (Fig. 71C). Only 1 whorl visible, forming the entire shell. Anterior end of the shell rounded. Umbilicus closed. Aperture long, wide anteriorly, narrowing gradually at about 1/4 of its length. At its apical end, the aperture bends over the apex of the shell and the parietal wall forms a blunt prolongation that completely covers the apex. Columellar margin slightly twisted with a small blunt denticle in some specimens (Fig. 71D). Sculpture of 8-12 irregular spiral grooves at the anterior end of the shell, which are not clearly visible in all specimens. The rest of the shell is covered with faint spiral grooves. There are also numerous fine growth lines all over its surface. Colour uniformly shiny whitish.

Anatomy. The digestive system contains 3 tuberculate, unequal gizzard plates (Fig. 73A). There is no radula.

REMARKS. — The material here examined resembles the original description of Cylichna (Volvulella) sulcata by Watson (1883) and subsequent redescription by Watson (1886), and it is provisionally assigned to this species. The shells included in this study show remarkable morphological variability and bathymetric range, but I have been unable to find consistent differences that would allow further separation of morpho-species. All the specimens studied share with the type material of Retusa sulcata a blunt prolongation of the parietal wall that completely covers the apex and several irregular spiral grooves on the anterior end of the shell, not present elsewhere. It is possible that additional material and anatomical information would allow detection of several species within the forms here assigned to R. sulcata . In the meantime they are all included in the same species.

Retusa sulcata belongs to a group of species of Retusa in which the aperture bends over the apex of the shell and the parietal wall forms a blunt prolongation that completely covers the apex. These species have been previously classified in Cylichnina . However, the anatomy of R. sulcata with 3 tuberculate, unequal gizzard plates is similar to that of other species of Retusa and it is therefore placed in this genus.