Peraclis depressa (non Vayssiére, 1913) Meisenheimer, 1906a
Overview
This is a pelagic snail with a left coiled shell, 0.3 cm high; it has 3 whorls and a deep suture without radial crests. The spire is depressed. A short keel ends in a distinct aperture tooth. The aperture is wide, the base of the aperture is pointed towards the keeled rostrum. The shell surface shows a regular structure of spiral lines which sometimes constitutes a reticulate pattern. The wings are fused into a swimming plate. This species lives usually at great depths in the Atlantic Ocean (Peraclis depressa).
Taxonomic Description
The shell is only slightly elongate and composed of three whorls with a deep suture. The spire is depressed, with whorls quickly increasing in size. A tooth-like protrusion is visible in the inner angle of the upper aperture border which is turned upwards and lies close to the apex. The aperture tooth has a keel which runs only over a short distance, along the upper whorl. Radial striae between the suture and keel are lacking. Outer aperture border regularly rounded. Columella provided with a very strong keel which continues into the rostrum; the columellar membrane is relatively well developed, but not broad. The umbilicus is clearly visible and wide. The rostrum is invisible in apical view. The shell surface has a regular structure of spiral lines which sometimes constitutes a reticulate pattern. The colour of the shell is white, only large specimens have a yellowish apex, the keel is horny to yellow. The operculum, with five whorls, has no radial striae.
Shell measurements of the type specimen: height 3.0 mm, maximum diameter 2.5 mm.
Juveniles
The juveniles have a small left coiled shell. A special description is not available.
Reproduction
This species is a protandric hermaphrodite.
Ecology
This species is phytophagous and mesopelagic.
Distribution
This species is typical for the E-Atlantic occurring in the eastern and southern basins, see the Peraclis depressa map. There is no proof of its occurrence in equatorial currents.
Types
Peraclis depressa Meisenheimer, 1906: 125, pl. 5, fig. 12.
Syntypes: HMEB S6725a, 3 spec., HMEB 56725b, 1 spec., HMEB 56725C, 1 spec. (alcohol collection) (Dr. Kilias in let.).
Type locality.: 11°S 19°W; 32°5'S 8°30'W ; 21°N 32°W. Coll.: CDSE stat. 11-X-I901; stat. S-XI-1901; stat. 13-X-I903.