Observation by SEM of the carapace microstructure of crabs showed, in the past, numerous differences at a specific level (i.e. in the genus Ebalia and Liocarcinus) as described by Spanò et al. (1995, 1999). The aim of this study is to describe the carapace micromorphology of some crab species of very different genera and species. A critical analysis of ecological data and morphological parameters is carried out in order to determine if the differences have adaptive significance.