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Atlanta pacifica Tokioka, 1955b

Overview

This is a large dextrally shelled, pelagic snail, 0.3 cm in diameter with large eyes and a single swimming fin. There are 4.5 whorls. The shell is strongly flattened and keeled. The spire is straight and purple. The spire of the operculum is relatively small. It is a carnivore predating on relatively large zooplankton. This species occurs in warm waters of the Pacific Ocean (A Atlanta pacifica young specimen after Tokioka).

Taxonomic Description

This species is closely related to Atlanta gaudichaudi, and the shell has the same structure and 4.5 whorls. The spire is nearly straight and purple. The shell is white except for some brown along the keel base. The whorl formula (cf. Tokioka, 1961) varies between 1 : 0.23 : 0.10 and 1 : 0.25 : 0.13, while this formula applied to the body (cf. Van der Spoel, 1972a) varies between 1 : 1.5 : 2.5 : 4 and 1 : 3 : 5. 5 : 10. Two, up to 2.5 whorls, are seen from underneath. The apical angle of the spire is up to 116°. The keel penetrates slightly (only 0.25 whorls distance) in between body whorl and spire (Atlanta pacifica, Atlanta pacifica oral view), it is, however, rather low. Umbilicus small and narrow.
Shell diameter up to 2.6 mm.

Juveniles

The juveniles have a small, dextrally coiled shell. A special description is not available.

Reproduction

In this species the sexes are separate.

Ecology

This species is carnivorous and epipelagic.

Distribution

It is too poorly studied to discuss its zoogeography. It is known from the NW-Pacific Ocean and probably from the Arabian Sea.

Types

Atlanta pacifica Tokioka, 1955b: 249, pl. 17, figs. D-G.
Types are not indicated.
Type locality: Southern waters off Japan. Coll.: Sôyô-Maru cruises (1934-1939).

Atlanta pacifica