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Protatlanta souleyeti (Smith, 1888a)

Overview

This is a small, dextrally shelled, pelagic snail, 0.1 cm in diameter with large eyes and a single swimming fin. The teleoconch is calcified but the keel is cartilaginous. The shell has 3.5 whorls and is strongly flattened and keeled. The spire of the operculum is in the medial line. It is a carnivorous species predating on relatively large zooplankton. This species occurs in the warm waters of all oceans (Protatlanta souleyeti).

Taxonomic Description

The right coiled calcareous shell is transparent and has some faint spiral striae. The umbilicus is wide. The keel is cartilaginous and it ends abruptly a little distance before the aperture border; it extends over half the circumference of the shell. The operculum is rounded triangular with the nucleus in the medial line. The suture is brownish, and the inner whorls show a much diluted buff colour. The head parts of the soft body are large in relation to the coiled visceral parts. The eyes are type A and the tentacles are short. The radula, with unicuspoid median plate, resembles the intermediate and lateral plates of the "Atlanta type"(Protatlanta souleyeti radula). The intermediate teeth has a comb. The operculum is of type A has 6 to 7 spiral lines on the nuclear whorls, except the first one. The adult shell has up to 3.5 whorls.
The shell diameter (keel excluded) is 1 to 1.5 mm.

Juveniles

The juveniles have a small dextrally coiled shell. The spire is relatively high, and nearly smooth, but spiral lines composed of small dots are present. The operculum has 6 to 7 spiral lines. The velum has 6 broad lobes.

Reproduction

In this species the sexes are separate.

Ecology

This species is carnivorous and epipelagic.

Distribution

The distribution of this species is similar to Oxygyrus keraudreni and it is found in Atlantic, Mediterranean and Indo-Pacific. The discontinuous pattern seems to reflect the true distribution and is not due to insufficient data. In the central Pacific, for example, the species appears to be absent, see the Protatlanta souleyeti map. The Mediterranean populations are sometimes considered a separate species but here considered as Protatlanta souleyeti.

Types

Atlanta souleyeti Smith, 1888: 43.
Syntypes: BMNH 1888.8.17.111-117, 7 spec. (mounted dry).
Type locality: off Sombrero Is, 18°24'N 63°28'W. Coll.: CCHE stat. 23.

Protatlanta souleyeti