Chromatic polymorphisms in shells may be associated with adaptive characteristics in molluscs. Colouring among Hastula cinerea reveals different patterns in large aggregations of individuals. Although the impacts of temperature are considered critical in the intertidal region, selective effects associated with colouring in H. cinerea shells, in addition to possible physiological consequences, remain an open issue. In this context, H. cinerea is a viable evolutionary model for investigating selective processes related to chromatic polymorphism in shells given its abundance and biological characteristics. Individuals from the same population were classified into three groups according to shell colour: light, reddish and dark. They were then examined with regard to frequency of colour morphs and morphological patterns in each group. Reddish and light-coloured specimens were the most abundant, while those with dark coloration were less common and morphologically distinct from the first two colour morphs. Morphological differences in the anterior region of dark shells, which may be associated with movement ability and lower frequencies in these specimens, suggest possible selective effects on types that are less reflective to light in the intertidal zone.
