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 : 635-636

“ Acteon “ sp. 5

Figs 22E, 23

MATERIAL EXAMINED. — Indonesia. KARUBAR: stn DW 28 , Kai Islands , 05°31’S, 132°54’E, 448-467 m, 1 dd .

Tonga. BORDAU 2: stn DW 1552, S of Nomuka Islands, 20°38’S, 174°58’W, 491-500 m, 1 dd (Fig. 22E).

DISTRIBUTION. — Shells collected only from Indonesia and Tonga (Fig. 23), in 467-491 m.

DESCRIPTION. — Shell morphology. Length 5.5 mm, width 3 mm (largest specimen examined). Shell fragile, short, oval, with convex sides (Fig. 22E). Body whorl large, about 4/5 of the shell length. Spire short with 2 whorls. Suture slightly channeled. Umbilicus closed. Aperture wide and long, wider anteriorly, about 3/4 of the body whorl

length. Columellar margin slightly thickened, with a single fold. Sculpture of several punctuated spiral grooves. The punctuations are small, oval, and separated from each other within each groove. The grooves are separated by gaps, several times wider than the grooves. Colour uniform dirty white to pale brown.

Anatomy. Unknown. All shells collected lacked soft parts.

REMARKS. — The two shells of “ Acteon ” sp. 5 here examined could belong to two different species but are here maintained in the same taxon because of the lack of distinctive differences. The shell from Tonga has a smaller tooth on the columella and the spiral grooves are more densely arranged than in the specimen from Indonesia. Also, the shell from Indonesia is darker. Anatomical information is necessary to determine the taxonomic position of these two shells.

“ Acteon ” sp. 5 most resembles Acteon chrystomatus n. sp. in overall shell morphology, colouration and sculpture, but the spire and the aperture of “ Acteon ” sp. 5 are much shorter.

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