Acteon, Montfort, 1810

Valdés, Ángel, 2008, Deep-sea “ cephalaspidean ” heterobranchs (Gastropoda) from the tropical southwest Pacific, Mémoires du Muséum national d'Histoire naturelle 196, pp. 587-792 : 633

“ Acteon ” sp. 2

Figs 22B, 23

MATERIAL EXAMINED. — Philippines. MUSORSTOM 2: stn DR 34, 13°28’N, 121°12’E, 155-167 m, 2 dd .

DISTRIBUTION. — Collected from the Philippines (Fig. 23), in 155-167 m.

DESCRIPTION. — Shell morphology. Length 3.2 mm, width 1.6 mm (largest specimen examined). Shell thin, oval, with convex sides (Fig. 22B). Body whorl large, about 3/4 of the shell length; spire short with only 1 whorl. Suture slightly channeled. Umbilicus narrow, partially covered by an expansion of the columellar margin. Aperture wide and short, wider anteriorly, about 3/4 of the body whorl length. Columellar margin slightly thickened, short, with a small fold. Sculpture of a few punctuated spiral grooves. The punctuations are small, oval, and partially fused to the next one within each groove. The grooves are separated by gaps that increase in width towards the centre of the spire. Colour uniform pale brown.

Anatomy. Unknown. All shells collected lacked soft parts.

REMARKS. — “ Acteon ” sp. 2 most resembles Bathyacteon aequatorialis (Thiele, 1925) in having a fragile shell with narrow, separate spiral grooves, composed of small, oval punctuations. Differences between these two species include the smaller number of spiral grooves in “ Acteon ” sp. 2, which are more separate, and the presence of a small umbilicus partially covered by an extension of the columella in this species. Because of its small size, it is possible that “ Acteon ” sp. 2 is a juvenile of another Indo-Pacific species, but examination of complete specimens is necessary to confirm this point.

A definitive generic placement for this species is not possible until complete specimens become available for study.