Acteocina gracilis (A. Adams, 1850)

Valdés, Ángel, 2008, Deep-sea “ cephalaspidean ” heterobranchs (Gastropoda) from the tropical southwest Pacific, Mémoires du Muséum national d'Histoire naturelle 196, pp. 587-792 : 709-710

Acteocina gracilis (A. Adams in Sowerby, 1850)

Figs 59E, F, 60C, D, 61

Bulla gracilis A. Adams in Sowerby, 1850 [in 1848-50]: 569, pl. 121, fig. 36.

TYPE MATERIAL. — Not examined .

TYPE LOCALITY. — China Seas .

MATERIAL EXAMINED. — Coral Sea. MUSORSTOM 5: stn 349, Passage, 19°00’S, 163°14’E, 386-400 m, 8 dd.

Chesterfield Islands , 19°34’S, 158°34’E, 275 m, depth, 2 dd. New Caledonia proper. VAUBAN: stn 40, 22°30’S, 166°24’E, North of New Caledonia. LAGON: stn 502, Lagon Nord, 250-350 m, 1 dd . — MUSORSTOM 4: stn DW 203 , 22°36’S, 19°08’S, 163°30’E, 190 m, 1 dd . — MUSORSTOM 4: stn DW 167°05’E, 105-110 m, 1 dd . — LAGON: stn 830, Secteur de 149, 19°08’S, 163°23’E, 155 m, 1 dd; stn DW 150 , 19°07’S, Poindimié, 20°49’S, 165°19’E, 105-110 m, 1 dd . — BATHUS 1 : 163°22’E, 110 m, 4 dd; stn DW 151 , 19°07’S, 163°22’E, 200 stn DW 674 , Grande Passe de Touho , 20°49’S, 165°19’E, 105- m, 3 dd; stn CC 173 , 19°02’S, 163°19’E, 250-290 m, 1 dd; stn 110 m, 1 dd; stn CP 713, Passe SE de Ngoe, 21°45’S, 166°37’E, CC 174 , 19°00’S, 163°18’E, 365 m, 3 dd; stn CC 175 , 18°59’S, 250 m, 1 dd . — BATHUS 2 : stn DW 715 , Ile des Pins , 22°39’S, 163°17’E, 355 m, 23 dd, 1 lv, destroyed to dissect the reproduc- 167°11’E, 202-227 m, 1 dd; stn CP 755, Passe de Dumbéa, tive system (Figs 60 C, D) . — BATHUS 4 : stn DW 903 , Grand 22°22’S, 166°14’E, 495 m, 2 dd .

Loyalty Ridge. BATHUS 3: stn DW 790, Mont J, 23°49’S, 176°08’W, 415-420 m, 4 dd; stn DW 635, SW Pacific 13°49’S, 169°48’E, 685-715 m, 3 dd; stn DW 793, 23°47’S, 169°49’E, 179°56’W, 700-715 m, 2 dd.

731-751 m, 5 dd. Tonga. BORDAU 2: stn DW 1523, Eua, 21°18’S, 175°00’W, 300- Vanuatu. MUSORSTOM 8: stn DW 976, 19°25’S, 169°27’E, 302 m, 1 dd; stn DW 1531, 21°12’S, 174°56’W, 970-983 m, 1 160-182 m, 17 dd; stn DW 1094, 15°08’S, 167°12’E, 312-314 dd; stn DW 1537, 21°41’S, 175°19’W, 391-421 m, 2 dd; stn DW m, 1 dd; stn DW 1100, 15°05’S, 167°10’E, 258-265 m, 1 dd; stn 1552, S of Nomuka Islands, 20°38’S, 174°58’W, 491-500 m, 1 DW 1106, 15°05’S, 167°12’E, 305-314 m, 2 dd. dd; stn DW 1586, Vava‘u Islands, 18°34’S, 173°55’W, 440-487 Fiji. BORDAU 1: stn DW 1469, 19°40’S, 178°10’W, 314-377 m, m, 1 dd; stn DW 1587, 18°37’S, 173°54’W, 309-400 m, 2 dd; 1 dd. stn DW 1601, centre of Ha‘apai Islands, 20°50’S, 174°57’W, Wallis and Futuna. MUSORSTOM 7: stn DW 505, Futuna Is- 200-487 m, 1 dd; stn DW 1611, Seamount, 23°00’S, 175°47’W, land 14°19’S, 178°04’W, 245-400 m, 1 dd; stn DW 601, Wallis 278-323 m, 1 dd; stn DW 1612, 23°02’S, 175°47’W, 327-342 m, Island, 13°19’S, 176°17’W, 350 m, 3 dd; stn DW 604, 13°21’S, 1 dd (Figs 59E, F).

DISTRIBUTION. — Found in China, Philippines and Japan (Habe 1955). Records herein from the Coral Sea, Fiji, New Caledonia, Tonga, Vanuatu and Wallis and Futuna (Fig. 61), in 110-970 m, live in 355 m.

DESCRIPTION. — Shell morphology. Length 11 mm, width 4 mm (largest specimen examined). Shell solid, elongate, fusiform, with almost parallel sides (Fig. 59E). Body whorl very large; spire conical, variable in length, with 2-3 whorls. Suture canaliculate. Protoconch flattened, about 1.2 whorls and 150 Μm in diameter (Fig. 59F). It is only attached to the teleoconch by the aperture. Umbilicus closed. Aperture very long, about 7/10 of the shell length, narrow, wider anteriorly, narrowing gradually towards the posterior end. Columellar margin thickened, oblique, with a long, thin callus running from its anterior end to about 1/3-1/5 of the aperture length. Sculpture of fine spiral lines, crossed by faint axial lines, not visible in all specimens. Colour uniformly whitish.

Anatomy. The digestive system contains 3 smooth and irregular gizzard plates, all of them similar in shape and size (Fig. 60D). The radular formula is 12 x 1.0. 1 in a specimen from New Caledonia (MUSORSTOM 4 stn CC 175). The lateral teeth are hook-shaped with a number of small denticles on the single, curved cusp (Fig. 60C).

REMARKS. — Comparison of the material here examined with the remaining syntype of Acteocina gracilis illustrated by Higo et al. (2001), confirms that they belong to the same species.

Acteocina gracilis is characterized by its fusiform shell with an elongate callus on the aperture. Acteocina fusiformis A. Adams in Sowerby 1850, figured by Hori (2000b) is probably a synonym, but that determination must await further study.