A number of studies undertaken on the highly polymorphic intertidal mollusc Clithon oualaniensis reported that colour-morph frequencies varied on a regional basis in the Indo-Pacific region (Gruneberg, 1976, 1978, 1979). Our study examined colour-morph variation on a local scale in the same species and demonstrated that a level of variation similar to the regional variation described by Gruneberg was present in Clithon populations collected from different microhabitats at a single locality in northeastern Queensland. An examination of genetic differentiation (using allozyme electrophoresis) of the same populations failed to identify an association between genotype and microhabitat and confirmed that Clithon populations at least on a local scale belong to a single gene pool. Factors that influence the distribution of morphs at particular sites are most likely to be such ecological factors as differential predation. The results of this study indicate that relationships between environmental variables on a regional scale and colour-morph frequencies in Clithon need to be reassessed and the extent of local variation studied intensively.