Figure 6

Evolutionary hypothesis of the shell-coiling mechanism in Gastropoda. The most recent common ancestor of Gastropoda acquired the asymmetric dpp expression pathway in the mantle at one stage (orange line). Later, the Patellogastropoda lost this pathway and the non-coiled shell shape evolved in this group (blue line). Moreover, other species with non-coiled shells in Vetigastropoda, Caenogastropoda or Heterobranchia most likely evolved like Patellogastropoda (broken blue lines).