The nervous system of bivalve molluscs, such as toothless molluscs, is more organized than that of gastropods. Why?

This is due to a partial reduction of the body, namely the absence of a head, and low mobility. The toothless in the nervous system has three pairs of nerve nodes, and the gastropods have 5, located in the head and body, twisted into a spiral. Bivalves, from living in one place, have poorly developed sense organs, only some species have eyes (for example, scallops). Gastropods have well-developed sense organs, because they rely on them as they move through the substrate.