Atlanta gibbosa Souleyet, 1852a
Overview
This is a medium sized dextrally shelled, pelagic snail, 0.4 cm in diameter with large eyes and a single swimming fin. The shell is large, strongly flattened and keeled. There are 7 whorls. The spire is large and slightly oblique, and like the rest of the shell colourless, it shows no spiral sculpture. The operculum has a clear spire. It is a carnivore predating on relatively large zooplankton. This species occurs in warm waters of the Indian Ocean (Atlanta gibbosa).
Taxonomic Description [after Richter, 1990]
Medium sized shells with the keel penetrating over a distance of a half whorl in between the preceding whorl. The spire is large but only slightly oblique. The clear suture is deep. The apical angle is 85°. The sides of the spire whorls are slightly concave. There are up to seven whorls. The umbilicus is wide and the underside of the shell is not flat. The keel is high, not steep ending, and stops far from the aperture. There is no sculpture except for growth lines. The spire whorls are not decalcified. The operculum (type B) is oligogyre and very thin. The eyes (type B) and lens are very large. The radula is ribbon-shaped, the width shows an increase angle of 15°. The median tooth has a thin, long median cusp. The lateral teeth show a inner cusp and a large thin additional cusp. There is sexual dimorphism in the radula: in females the additional teeth are shorter than the lateral teeth and have only a curved tip; in males they are smaller and curved over their whole length.
Shell diameter up to 4 mm.
Juveniles
The juveniles have a small, dextrally coiled shell. The Atlanta gibbosa juvenile has a rather smooth broad conical shell.
Reproduction
In this form the sexes are separate.
Ecology
This species is carnivorous and epipelagic.
Distribution
This species is found in the Indian ocean, see the Atlanta gibbosa map.
Types
Atlanta gibbosa Souleyet, 1852: 386, pl. 21, figs. 1-8.
Syntypes: are probably present in MHNP.