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Atlanta fusca Souleyet, 1852a

Overview

This is a medium sized dextrally shelled, pelagic snail, 0.2 cm in diameter with large eyes and a single swimming fin. The shell is large, strongly flattened and keeled. There are 5 whorls. The spire is high but small, and like the rest of the shell of a buff colour, it shows spiral sculpture (Atlanta fusca 1). The operculum has a small spire. It is a carnivore predating on relatively large zooplankton. This species occurs in warm waters of all oceans.

Taxonomic Description

The inflated solid shell with a buff colour, composed of about 5 whorls is very small. Aperture rounded (Atlanta fusca SEM). The spire is high but relatively small which is shown by the whorl formula varying between 1:0.29:0.14 and 1:0.36:0.21. The spire has 5 to 7 wavy spiral lines. The high, white keel shows a slight tendency to penetrate between the spire and body whorl. The apical angle of the spire is somewhat smaller than in the other species of this group, being about 90°, the spire is also higher than in the other species. The eyes (type A) are not broad based but in the contrary are slightly cylindrical with a relatively small lens. The thick operculum is, in young specimens, oval shaped, but in adults it is relatively broad. The axial angle is straight or obtuse. The gyre is large, but the central part is small and situated in the upper axial half shifted a little to the anterior side. The lateral radula teeth are bicuspoid. The operculum (type A) is very thick (Atlanta fusca operculum, Atlanta fusca operculum1).
Shell diameter up to 1.7 mm.

Juveniles

The juveniles have a small dextrally coiled shell. The reddish/brown larval shell is not as depressed as in the other species. On the Atlanta fusca protoconch more than 3 finely undulating spiral lines are present, one or two are continuous while the others are interrupted (Atlanta fusca juvenile). The velum has 6 broad lobes (Atlanta fusca juv.).

Reproduction

In this species the sexes are separate.

Ecology

The species is carnivorous and epipelagic.

Distribution

This species is a common and widely distributed in warm water, see the Atlanta fusca map.

Types

Atlanta fusca Souleyet, 1852: 389 (1841) pl. 21, figs. 15-29.
Lectotype: MHNP (alcohol collection), Paratypes: MHNP 9 specimens (alcohol collections).
Type locality: restricted to the Indian Ocean Coll.: Eydoux and Souleyet.

Atlanta fusca