Consecutive underwater mappings of specimens of the calcareous spongeClathrina cerebrumwere performed within a plastic quadrat (1 m‐side) fixed to a cliff wall of the Portofino Promontory (Ligurian Sea, Italy) at a depth of 4 m. The typical clathrate forms ofC. cerebrumwere present only during the cold season (from autumn to spring). In summer, species survival depends upon minute forms that represent a successful strategy for withstanding the heat crisis. Investigations carried out with scanning electron microscopy allowed two types of minute forms to be distinguished: type A, which shows the same architecture as the clathrate sponges, and type B, with characteristic quadriradial symmetry. The morphology of both forms is consistent with their different origin: by fragmentation (type A) and by sexual reproduction (type B). Comparative analysis revealed variations in the dimensional range of the porocyte openings. These findings support the hypothesis that the dynamics of water flow differs between clathrate and minute forms.