in Sri Lanka - Ministry of Environment

The Taxonomy and Conservation Status of the Land snails in Sri Lanka:K. B. Ranawana 1 and T. G. M. Priyadarshana 21Department of Zoology, University of Peradeniya, Peradeniya210/8 Theleawala Road, Mount LaviniaIntroductionMolluscs (snails and slugs) are the second most diverse animal phyla after arthropods (Solem,1981; Emberton et al., 1997). Majority of the molluscs are aquatic (marine and freshwater),whereas only 25% comprise of terrestrial species (Emberton et al., 1997). Class Gastropodais the largest class of mollusks, which is considered as the most successful of all molluscanclasses and they have colonized a wide range of habitats including land, freshwater andmarine environments. Prosobranchia, Opisthobranchia and Pulmonata are the three majorsubclasses of class Gastropoda. Majority of Opisthobranchs are marine inhabitants. Molluscsare important elements in the studies on mechanisms of evolution and examining the effects ofecology on evolutionary change (Crampton, 1932; Cain and Sheppard 1950; Cain and Currey,1963; Cowie, 1992; Johnson et al., 1993). Their low vagility also makes them suitable asindicators for biogeographical studies of early tectonic events (Solem, 1981). Due to their lowmobility, land snails have become models for studying the effects of pesticides and influenceof the activities of man in altering the environment.Of the 253 species of land snails recorded from the country, 166 species belong to Sub classPulmonata and is represented by 28 families. The remaining 87 species belong to the subclassProsobranchia, which is represented by four families. This indicates that the pulmonate groupdominates land snails in Sri Lanka. The families Ariophantidae (mainly Cryptozona andEuplecta) with 50 species and Glessulidae (22 species) are the largest pulmonate familiesfound in the country. Cyclophoridae (54 species) is the largest Prosobranch family.TaxonomyTaxonomic status of some of the land snail groups in Sri Lanka needs to be thoroughly revised.For instance ‘Digoniaxis’ cingalensis (Benson 1863) was described from a single specimencollected by Edgar Layard close to Matale, North of Kandy, Sri Lanka. The taxonomic status of D.cingalensis remains a mystery because the type species of the genus Digoniaxis Jousseaume,1894 was found on a beach near Aden, Yemen, which proves to be a marine pyramidellid.DistributionA significant portion of Sri Lankan snail fauna consists of Gondwana relicts, with origins datingback prior to the breakup of the southern super-continent over 100 million years ago (Naggset al., 2003). Sri Lankan land snails are considered as the most distinct in the South AsianRegion, despite their faunistic affinities with the Indian mainland (Naggs et al., 2003). Speciesrichness and endemicity are high among Sri Lankan land snails (Naggs et al., 2003). Of the253 species of land snails recorded from the country, majority (205 species, approximately81%) are categorized as endemic according to the current available data. Further five landsnail genera are considered to be endemic to Sri Lanka. These include four stylommatophoran65