Acteon ionfasciatus, 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

Acteon ionfasciatus n. sp.

Figs 1C-F, 3

TYPE MATERIAL. — Holotype MNHN 20260 and 33 paratypes MNHN 20261-20264, 1 paratype LACM 2975 .

TYPE LOCALITY. — Philippines, 11°58’N, 121°06’E, 448-466 m [MUSORSTOM 3: stn CP 118] .

MATERIAL EXAMINED. — Philippines. MUSORSTOM 2: stn ( LACM 2975 ); stn DR 140, 11°43’N, 122°34’E, 93-99 m, 29 dd, CP 36, 13°31’N, 121°24’E, 569-595 m, 1 dd, paratype ( MNHN paratypes ( MNHN 20263 ; Figs 1E, F).

20261); stn CP 44, 13°23’N, 122°20’E, 760-820 m, 1 dd, 1 lv Indonesia. KARUBAR: stn DW 28, Kai Islands, 05°31’S, (destroyed to dissect the radula), paratypes ( MNHN 20262; Fig. 132°54’E, 448-467 m, 1 dd, paratype ( MNHN 20264).

1D). — MUSORSTOM 3: stn CP 118, 11°58’N, 121°06’E, 448- New Caledonia proper. BATHUS 4 : stn DW 948 , Passe de 466 m, 2 dd, holotype ( MNHN 20260 ; Fig. 1C) and 1 paratype Hienghène, 20°33’S, 164°57’E, 533-610 m, 1 dd .

DISTRIBUTION. — Philippines, Indonesia and New Caledonia (Fig. 3), shells only in 99-760 m, live in 760-820 m.

DESCRIPTION. — Shell morphology. Length 30 mm, width 13 mm (holotype). Shell thin, elongate, with convex sides (Fig. 1C). Body whorl large; spire elongate, conical, variable in length, with 4-6 whorls. Suture channeled. Protoconch globose, about 1.2 whorls and about 500 Μm in diameter (Fig. 1E). Umbilicus closed. Aperture narrow, wider anteriorly, and long, about 4/5 of the body whorl length. Columellar margin thickened, slightly oblique, with a small, simple fold. Sculpture of a number of punctuated spiral grooves (Fig. 1F). The punctuations are conspicuous, irregular, almost rectangular, and situated next to each other within each groove. The grooves are separated by gaps as wide as the grooves themselves, and occasionally narrower grooves are intercalated between the main grooves. Colour brownish, with a wide, spiral, pale violet band on the centre of the body whorl, surrounded by a paler area. Some specimens are bleached and show no traces of colouration.

Anatomy. The radular formula is 117 x 58.0. 58 in a specimen from the Philippines (MUSORSTOM 2 stn CP 44). The radular teeth are all similar in shape and size, with an elongate base and 5-7 pointed cusps (Fig. 1D).

REMARKS. — Two other Indo-Pacific species with a similar shell shape are Japonacteon sieboldii (Reeve, 1842) and Acteon archibenthicola Habe, 1955 , both illustrated and described by Hori (2000a). Japonacteon sieboldii differs from Acteon ionfasciatus by having a conspicuous umbilicus, a white subsutural band and by lacking a pale violet band. Acteon archibenthicola is a uniformly pinkish species with a narrow umbilicus.

Acteon ionfasciatus 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.

Acteon cumingii A. Adams, 1854 from the western Atlantic has a radular morphology very similar to that of Acteon ionfasciatus , with several sharp cusps on each lateral tooth (see Marcus 1972). However, the outermost teeth of A. cumingii have very short bases and elongate denticles, whereas those of A. ionfasciatus are similar in shape and size. Also, Acteon turritus Watson, 1886 from the eastern Atlantic, a species assigned to Tomlinula Strand, 1932 by Bouchet (1975), has very different radular teeth, with only 2 cusps on the inner lateral teeth, and reduced and simple outermost teeth.

ETYMOLOGY. — From the combination of the Greek noun for violet (ion) and the Latinization of the Greek noun for band (fascia), in reference to the violet band present on the shell of this species.