Familia Atlantidae

Family Atlantidae Wiegmann and Ruthe, 1832

Atlantidae is composed of three genera (Atlanta, Oxygyrus, Protatlanta). The taxonomy of Atlanta in this programme is mainly based on the publications by Richter. A dextrally coiled calcareous, aragonite shell is formed and this shell is large enough for the entire animal to retract into. The flatly coiled whorls usually increase rapidly in size and the body whorl has a keel. This keel is composed of two lamella placed over a slit in the body whorl through which the mantle and gills protrude outwards. Transverse growth lines are usually seen and spiral striation is sometimes present on the first whorls. Depending on the species the keel sometimes penetrates between the body whorl and the spire. An operculum is always present.
In Oxygyrus keraudreni the shell only consists of conchioline; even the calcium from the protoconch is reabsorbed in adults, a glassy somewhat flexible "shell" remains. In Protatlanta souleyeti the shell is calcareous but the keel is not calcified. It is not clear if the atlantid shell, as found in Atlanta inclinata, is the original type or that of the Protatlanta shell. The non-calcareous character of Oxygyrus is certainly a secondary character developed as an adaptation to pelagic life. The shape of the visceral parts are coiled to reflect the shape of the shell.
The anatomy of Atlanta is typical of the prosobranch type. Liver and gonads are situated in the tip of the shell. The duct between gonad and sexual aperture passes an accessory sexual gland. The heart (ventricle and atrium) and kidneys are found dorsally to this gland. Gills are found in the mantle cavity and protrude through the slit of the shell. The eyes are, with the cerebral ganglia, the best visible structures. Before the eyes the buccal mass with radula and attached salivary glands is seen. The stomach and intestine are found between liver and mouth, the latter ending in the anus. The columellar muscle connects the shell with the foot and fin (especially operculum and sucker).

[3 genera]