Retusa crispula (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 : 731-732

Retusa crispula (Watson, 1883)

Figs 71E, F, 72, 73B

Cylichna crispula Watson, 1883: 321 .

TYPE MATERIAL. — 5 syntypes BMNH 1887.2.9.2271-5 .

TYPE LOCALITY. — Rain Island , Cape York, Australia, 11°38’15”S, 143°59’38”E, 283 m [Challenger: stn 185b] .

MATERIAL EXAMINED. — North of New Caledonia. MUSORS- 650 m, 1 dd; stn CP 698, 20°34’S, 164°57’E, 491-533 m, 68 dd . — TOM 4 : stn CC 175 , 18°59’S, 163°17’E, 355 m, 8 dd, 1 lv des- BATHUS 2 : stn DW 717 , Ile des Pins , 22°44’S, 167°17’E, 350-393 troyed to dissect the gizzard plates (Figs 71E, F, 73B) . — BATHUS m, 14 dd; stn CP 755, Passe de Dumbéa , 22°22’S, 166°14’E, 495 4: stn DW 903 , Grand Passage, 19°00’S, 163°14’E, 386-400 m, 1 m, 26 dd; stn CP 760, 22°19’S, 166°11’E, 455 m, 1 dd; stn CP dd; stn DW 923 , 18°52’S, 163°24’E, 470-502 m, 1 dd. 761, 22°19’S, 166°11’E, 490-500 m, 40 dd .

New Caledonia proper. VAUBAN: stn 40, 22°30’S, 166°24’E, Loyalty Ridge. MUSORSTOM 6: stn DW 459 , 21°01’S, 167°31’E, 250-350 m,>100 dd . — BIOCAL: stn DW 41 , 22°45’S, 167°12’E, 425 m, 1 dd .

380-410 m, 6 dd. — CALSUB: pl. 20, SW of Ile des Pins , 22°53’S, Vanuatu. MUSORSTOM 8: stn DW 1045 , 16°54’S, 168°20’E, 167°23’E, 580 m, 2 dd; stn PL 22 , 22°53’S, 167°23’E, 606 m, 459-488 m, 6 dd .

1 dd. — BATHUS 1 : stn DW 683 , Passe de Hienghu , 20°35’S, Wallis Island. MUSORSTOM 7: stn DW 523 , Wallis Island , 165°07’E, 380-400 m, 14 dd; stn CP 695, Passe de Hienghène, 13°12’S, 176°16’W, 455-515 m, 1 dd; stn DW 594 , Banc Field, 20°35’S, 164°58’E, 410-430 m, 50 dd; stn DE 696, 20°34’S, 12°31’S, 174°20’W, 495-505 m, 2 dd; stn DW 604 , Wallis Island, 164°57’E, 497-520 m, 11 dd; stn DE 697, 20°34’S, 164°58’E, 570- 13°21’S, 176°08’W, 415-420 m, 10 dd .

DISTRIBUTION. — Originally described from Raine Island , Cape York, Queensland, northern Australia, in 283 m. Material herein collected from New Caledonia, Vanuatu and Wallis Island (Fig. 72), in 350-606 m, live in 355 m.

DESCRIPTION. — Shell morphology. Length 4 mm, width 1.5 mm (largest specimen examined). Shell fragile, oval to elongate, with slightly convex sides (Fig. 71E). Only 1 whorl visible, forming the entire shell. Anterior end of the shell rounded. Umbilicus closed. Aperture long, wide anteriorly, narrowing gradually at about 1/3-1/2 of its length. At its apical end, the aperture bends over the apex of the shell and the parietal wall forms a short prolongation that covers part of the apex, except for a narrow umbilicus (Fig. 71F). Columellar margin slightly twisted. Sculpture of numerous, faint and densely concentrated spiral grooves crossed by fine growth lines all over the shell surface. Colour uniformly shiny whitish.

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

REMARKS. — The material here examined is very similar to the original description and redescription of Cylichna crispula (see Watson 1883, 1886) and clearly belongs to this species. The most conspicuous feature of C. crispula is the presence of an apical umbilicus, partially covered by the prolongation of the parietal wall.

Watson (1886) placed this species in Cylichna but indicated that it was “deceptively like a Volvulla [= Volvulella ]”. Harry (1967) included Cylichna paupercula Watson, 1883 , another species with an apical umbilicus, in the genus Volvulella , arguing that the shell morphology and sculpture are more similar to those of Volvulella than Cylichna . Examination of the anatomy of the present material has revealed 3 tuberculate gizzard plates in the digestive system, similar to those in other species of Retusa . Therefore this species is here transferred to the genus Retusa .