Acteon chrystomatus, Valdés, 2008

Valdés, Ángel, 2008, Deep-sea “ cephalaspidean ” heterobranchs (Gastropoda) from the tropical southwest Pacific, Mémoires du Muséum national d'Histoire naturelle 196, pp. 587-792 : 593-594

Acteon chrystomatus n. sp.

Figs 2A-D, 3

TYPE MATERIAL. — Holotype MNHN 20256 and 38 paratypes MNHN 20257-20259, 5 paratypes LACM 2976 .

TYPE LOCALITY . — New Caledonia, Passe de Hienghu , 20°35’S, 165°07’E, 408-440 m [ BATHUS 1 : stn DW 687 ] .

MATERIAL EXAMINED. — North of New Caledonia. 497-520 m, 1 dd; stn CP 698, 20°34’S, 164°57’E, 491-533 m, 1 MUSORSTOM 4: stn DW 149 , 19°08’S, 163°23’E, 155 m, 6 dd dd; stn CP 701, Passe du Cap Baye, 20°58’S, 165°36’E, 302-335 & lv, paratypes ( MNHN 20257 ; Fig. 2D); stn DW 150 , 19°07’S, m, 1 dd; stn DE 705, 21°02’S, 165°38’E, 350-400 m, 3 dd . — 163°22’E, 110 m, 5 dd, paratypes ( LACM 2976 ); stn CC 175 , BATHUS 2 : stn CP 760, Passe de Dumbéa , 22°19’S, 166°11’E, 18°59’S, 163°17’E, 355 m, 1 dd . — BATHUS 4 : stn DW 903, 455 m, 5 dd .

Grand Passage, 19°00’S, 163°14’E, 386-400 m, 1 dd. Norkfolk Ridge. BATHUS 3 : stn DW 824 , Banc Jumeau Ouest , New Caledonia proper. VAUBAN: stn 40, 22°30’S, 166°24’E, 23°19’S, 168°00’E, 601-608 m, 4 dd . — BERYX 11 : stn CP 21, 250-350 m, 16 dd, paratypes ( MNHN 20259 ) . — BATHUS 1 : stn 24°44’S, 168°07’E, 430-450 m, 1 dd .

DW 687, Passe de Hienghu, 20°35’S, 165°07’E, 408-440 m, 17 Loyalty Ridge. BIOGEOCAL: stn DW 253, 21°32’S, 166°29’E, dd, holotype (MNHN 20256; Figs 2A-C) and paratypes (MNHN 310-315 m, 2 dd.

20258); stn DE 696, Passe de Hienghène, 20°34’S, 164°57’E,

DISTRIBUTION. — New Caledonia (Fig. 3), in 110-601 m.

DESCRIPTION. — Shell morphology. Length 5.5 mm, width 3 mm (holotype). Shell thin, oval, with convex sides (Fig. 2A). Body whorl large; spire short, conical, variable in length, with 2-3 whorls. Suture slightly channeled. Protoconch globose, about 1.2 whorls and 750 Μm in diameter (Fig. 2B). Umbilicus closed. Aperture wide and short, wider anteriorly, about 3/4 of the body whorl length. Columellar margin not thickened, short, with no folds or teeth. Sculpture of a number of punctuated spiral grooves (Fig. 2C). The punctuations are small, oval, and separate from each other within each groove. The grooves are separated by gaps that increase in width towards the posterior end of the spire. Occasionally narrower grooves are intercalated. There are 2 wide spiral grooves situated near the posterior end of the spire arranged next to each other, having very elongate punctuations. Colour uniformly pinkish, with a lighter band near the posterior end of the suture. Interior surface of the aperture with a yellowish tinge in some specimens.

Anatomy. The radular formula is 49 x 22.0. 22 in a specimen from New Caledonia (MUSORSTOM 4 stn DW 149). The radular teeth are all similar in size and shape. They have an elongate base and 10-12 thin and pointed cusps (Fig. 2D).

REMARKS. — Acteon chrystomatus is most similar to Acteon soyoae Habe, 1961 , from Japan, but the shell of A. soyoae is more elongate with a longer spire, and the sculpture is composed of more densely arranged spiral grooves leaving no gaps or smooth areas.

Acteon chrystomatus is placed in the genus Acteon because of the presence of a wide radula with numerous short teeth, similar to that of Acteon tornatilis (Linné, 1758) , the type species of the genus. For a description of the radula of A. tornatilis see Thompson (1976).

ETYMOLOGY. — From the combination of the Greek noun for mouth (stoma) and the adjective for golden (chryso), in reference to the yellowish colour of the aperture in some specimens of this species.