There are 3 distinct colour forms of the large land snail Acavus superbus:
They can be identified by the colour of the lip of the shell which is:
Acavus superbus can be readily distinguished from the 2 other species in the genus:
Shells of Acavus heamstoma (left) and A. phoenix.
In the field, Acavus may be confused with the closely related Oligospira, another large snail which is also endemic to Sri Lanka.
In Oligospira, however, the upper surface of the shell is flattened and compressed, whereas Acavus has a noticeably conical shell.
Oligospira polei shell
Acavus and Oligospira belong to a very ancient group of land snails, the Acavoid-Strophocheild clade, that has a history dating back to the break-up of the supercontinent of Gondwana more than 200 million years ago.
The modern-day representatives of this ancient clade have a distribution extending from South America to: