Introduction

Abstract

The phylum Mollusca is probably the third most successful animal group after the arthropods and the vertebrates. Slugs and snails belong to the class Gastropoda, generally characterized by having a distinct head with tentacles and eyes, a broad flattened foot and a dorsal visceral mass at least partly covered by the mantle. The mantle extends downwards to enclose a mantle cavity, which contains gills in aquatic gastropods. The visceral mass exhibits torsion to a varying degree and is often coiled and typically covered by a calcareous shell.