The distribution of molluscs on littoral rocks in Ceylon,with notes on their ecology

Molluscs inhabiting littoral rocks were collected from 43 stations around Ceylon, and 57 species belonging to 20 families were identified. An account is given of the nature and distrbution of littoral rocks around the island, and the stations examined. On each shore, the distribution of the molluscs was studied in relation to the broad zonation of the shores themselves and observations were made on plant and animal associations of each speices. The limits of the broad zones of the shores were defined with reference to biological indicators. Analysis of the data collected led to a classification of the rocky shores into three groups, each characterized by particular combinations of mollusc species and distinct patterns of shore zonation. Some molluscs were found to be distributed over the whole island, others to be common to two groups of shores only, and still others to be confined to a single shore type. An attempt has been made to explain the presence or absence of species on various groups of shores, and to explain discontinuities in distribution on the basis of environmental factors such as the nature of the substratum, degree of wave exposure, and weed cover. A key, based primarily on external features, has been devised for the identification of the species listed.