Widespread and large group (130 000 species: Mussels, snails, squids).

Limestone structures of molluscs have been formed since the cambrian period. In the course of evolution, some molluscs developed very complex and efficient structures. The organs of squids for example reach the level of differentiation of respective organs of vertebrates. In particular the eyes of squids and vertebrates are a good example for the development of similar structures starting from different conditions.