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Snail


Snail common name for the soft-bodied animals of the class Gastropoda, phylum Mollusca, having distinct head with one or two pairs of tentacles, a broad flat foot, mantle cavity and twisted visceral mass enclosed in a single halicoid shell often closed by an operculum. Included in this class are thousands of species that are terrestrial, marine or freshwater in habit. In the pulmonate snails the mantle cavity has been converted into a vascularized lung-like structure for gaseous exchange in air or secondarily in water. Terrestrial pulmonates have two pairs of retractile cephalic tentacles, and the eyes are situated at the tips of the hind pair (Stylommatophora). Aquatic pulmonates have only one pair of cephalic tentacles which may be contractile but not retractile and the eyes are situated at the bases of the tentacles (Basommatophora). Fossil records indicate that the gastropods first appeared in the Cambrian 570 to 500 million years ago, but it is not clear when the gastropod populations were established in Bangladesh territory.

A variety of snails

The shell varies greatly in length from 1 mm to 380 mm. About 50,000 species, of which 23,000 are marine, 22,000 terrestrial and 5,000 freshwater, have been reported from the world. Prevailing subtropical monsoon climate and rich vegetation as well as the natural rivers, streams, swamps, artificial lakes, water reservoirs, and 480 km long coastal line on the southern zone of the country with vast deep sea area provide good habitats for the land, freshwater and marine molluscs in Bangladesh. However, there is no consolidated report on how many snail species are there in Bangladesh. Ahmed (1990) and Jahan et al. (1990, 1993) reported 212 species of marine snails from the coastal waters of Bangladesh under 80 genera, 40 families and 5 orders.

A total of 26 terrestrial species (Cyclophoridae 5; Achatinadiae (exotic) 1; Enidae 1; Ariophantidae 2; Glessulidae 1; and Zonitidae 16); and 80 freshwater species (Neritidae 5; Viviparidae 8; Pilidae 3; Hydrobidae 5; Bithynidae 10; Stenothyridae 5; Thiaridae 22; Lymnaeidae 10; Ancylidae 1; and Planorbidae 11) have been recorded from Bangladesh. It is estimated that Bangladesh has more than 300 species of snails. The land snail Cyclophorus auranticus and C. aurora are confined to the evergreen hill forests of Sylhet District. The snails feed on the semi-decayed leaves of trees and remain active in day and night following the showers during the monsoon. They play a vital role in the conversion of organic materials into the soil components.

All the land snails undergo aestivation during dry season. Land snails, Macrochlamys indica and M. sequax are vegetable pests throughout the country. Recently, M sequax appears to cause heavy damage to the mulberry plant in the northern parts of Bangladesh. The Giant land snail, Achatina fulica was introduced in the garden of the Royal Asiatic Society, Calcutta from Mauritius in 1847 by the Choncologist Benson. The presence of this species has been reported from all the districts of the country except Mymensingh, Sherpur, Jamalpur, Kishoreganj and Maulvibazar. The snail have become a serious pest of vegetable crops, timber-yielding and ornamental plants. A. fulica is considered as a delicious protein rich food in western countries. Some tribal people of Bangladesh eat freshwater snail Bellamya bengalensis and Pila globosa. These snails are also utilized as supplementary feed for the exotic fish Clarias gariepinus, and domestic ducks almost throughout the year. Recently, chopped flesh of P. globosa is being used as supplemental feed for the prawns, Macrobrachium rosenbergii and Penaeus monodon. B. bengalensis, P. globosa, Lymnaea luteola, L. acuminata, L. stagnalis, Indoplanorbis exustus and Gyrulus convexiusculus harbour larval trematodes and other parasites which are injurious to birds, domestic animals, and man. Most of the marine snails have colourful and variously sculptured shells which are adorned to a variety of uses such as bracelets, necklaces, bangles, key bunch, astray, as trumpets (Turbinella pyrum, the chunk), for cameos carving, as curios, as mother of pearl, etc. [Md Sarwar Jahan]

Bibliography ATA Ahmed, Studies on the identity and abundance of molluscan fauna of the Bay of Bengal. Bangladesh Agriculture Research Council, Contract Research Project Report, 1990; MS Jahan, MA Mannan, and MN Mandal, Intertidal Molluscs of the Sundarbans, Bangladesh. Environment and Ecology 8(2): 603-607, 1990; MS Jahan, Some terrestrial and freshwater gastropods of Bangladesh with their ecological notes. Univ. J. Zool. Rajshahi Univ. 12: 65-71, 1993.