Taxonomy
The 3 different colour forms of Acavus superbus, superbus (left), grevillei (centre) and roseolabiatus (right).
There are 3 distinct colour forms of the large land snail Acavus superbus:
- superbus
- grevillei
- roseolabiatus
They can be identified by the colour of the lip of the shell which is:
- white with a golden-brown outer margin in superbus
- uniformly black in grevillei
- dark rose pink in roseolabiatus
Distinguishing Acavus superbus from closely related species
Acavus superbus can be readily distinguished from the 2 other species in the genus:
- The shell of A. haemastoma is boldly banded brown and white.
- A. phoenix is a larger species with a paler and more rounded shell and a glossy black body.
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
Acavoid-Strophocheild clade
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:
- Southern Africa
- Madagascar
- the Seychelles
- Sri Lanka
- eastern Australia