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Atlanta gaudichaudi Souleyet, 1852a

Overview

This is a medium sized dextrally shelled, pelagic snail 0.5 cm in diameter with large eyes and a single swimming fin. The shell is large, strongly flattened and keeled. The spire is smooth, small, and like the rest of the shell colourless. The operculum has a very small spire. It is a carnivore predating on relatively large zooplankton. This species occurs in warm waters of all oceans (Atlanta gaudichaudi 3, Atlanta gaudichaudi).

Taxonomic Description [based on Richter, 1993]

Shell flatly coiled, small, calcareous, transparent or opaque with a low blunt spire (Atlanta gaudichaudi 2); colourless or brown near the keel base with up to 4.5 whorls. The last whorl is relatively large compared to the preceding species (Atlanta gaudichaudi adult, Atlanta gaudichaudi lateral). The aperture diameter is also larger than in Atlanta peroni. The third whorl is, however, relatively small. The keel is high and ends steeply near the aperture. The spire is smooth except for growth lines and a small spiral line near the suture. The brownish base of the high keel does not insert strongly (Atlanta gaudichaudi swimming). The whorl formula (cf. Tokioka, 1961) varies between 1 : 0.23 : 0.09 and 1 : 0.47 : 0.28. The whorl formula for the soft body (cf. Van der Spoel, 1972) varies between 1 : 1.5 : 3:6 and 1 : 3 : 5.5 : 18. For this species Tokioka (1961) found two types of opercula, the narrow and the wide operculum type, however, it is micro-olygogyre. The apical angle of the spire is smaller than 100°. Eyes (type B) are cuboid but with a slightly broader base than in A. peroni. The Atlanta gaudichaudi radula formula is 2-1-1-1-2, there are 100 transverse rows. The median teeth of the radula (Atlanta gaudichaudi radula 2) broadly rectangular with a strong median cusp. The operculum (type B) is without dentation.
Maximum shell diameter 3-5 mm.

Juveniles

The juveniles (Atlanta gaudichaudi juv.) have a small, dextrally coiled shell with 3.5 smooth whorls except for one spiral line near the suture that starts on the second whorl. At this stage it is clear that the spire is slightly elevated. The velum has first 4, later 6, moderately broad lobes. The shell ranges from 0.04 to 0.40 mm in diameter and is colourless. (Newman, 1990) (Atlanta gaudichaudi protoconch, Atlanta gaudichaudi protoc).

Reproduction

In this species the sexes are separate.

Ecology

This species is carnivorous and epipelagic. It feeds on Creseis chierchiae and other Creseis species. See this Atlanta gaudichaudi feeding on Creseis v. virgula in Australian waters.

Distribution

It is probably an Indo-Pacific species, see the Atlanta gaudichaudi map.

Types

Atlanta gaudichaudi Souleyet, 1852: 397 (1841), pl. 19, figs. 29-34.
Lectotype: MHNP (alcohol collection). Paralectotypes: MHNP, 6 spec. (alcohol collection).
Type locality: Pacific Ocean. Coll.: Eydoux and Souleyet.

Atlanta gaudichaudi