Introduction

Atlantids are the most species-rich family of heteropods, containing over 60% of all species. They are microscopic (<1 cm shell diameter), and bear a coiled shell into which they can retract their bodies. After retraction into the shell, the shell aperture is closed off by a chitinous operculum attached to the opercular lobe of the foot. The head has a pair of large tentacles anterior to the eyes. A large muscular sucker, located on the posteroventral margin of the swimming fin, is used to hold prey fast while feeding. Atlantids are found primarily between the surface and 200 m in tropical to subtropical waters. Many species undergo vertical migration from daytime depths into shallower waters at night.

Brief Diagnosis

A family of heteropods with:

• Microscopic size (<1 cm shell diameter)
• Body retractable into coiled shell; shell aperture closed off by chitinous operculum
• Swimming fin with large, muscular sucker that is used to hold prey while feeding