The substratum is known to play an important role in the distribution of muddy shore molluscs. The mud snail Terebralia palustris occurs abundantly in the mangal at Nizampatnam (15" 54' N; 80° 43 'E) in the Krishna estuarine region on the east coast of South India. The response of this snail to different types of substrata viz. sand (100%), muddy sand (75% sand and 25% mud), intermediate (50 % sand and 50 % mud), sandy mud (25 % sand and 75 % mnd), mud (100 %) and plants, was studied. T. palustris was found to prefer the substrata with plants. The results are discussed and are compared with those of the other muddy shore forms.