These are the most complex of the mollusks. Squids, octopi belong to this group.
These are predators and feed on fish and other marine organisms. They have well developed nervous systems with a large eye and closed circulatory systems. Blood does not pool up and surround the organs here, it is pumped into the organ by tiny vessels.
Cephalopods are great swimmers and can propel themselves by filling up a hollow body cavity and squeezing it out to shoot them in a certain direction.