Bivalves have simple nervous systems with several small ganglia near the mouth, a few nerve cords, and simple sense organs. Cephalopods, however, are intelligent and have highly advanced nervous systems, which help them remember things for long periods of time. In most mollusks, there are two different sexes and fertilization is external. In these mollusks, eggs and sperm are released into the water and they find each other by chance. In gastropods, fertilization is internal.
Some mollusks are hermaphroditic, which allows for more efficient reproduction.