As we know Mollusca is a filum that includes many classes of organisms, characterized by a hard shell, among these we can find certain exceptions such as Cephalopoda where are located octopuses and squids, which actually have the characteristic shell of mollusk but is very different from other organisms like bivalves. Cephalopoda have the hard sell next to the head, in the inner part of the animal, for example in the squids is also located next to the head but is harder to distinguish as look like a hard transparent foil that runs along the head.