This makes the irritant smooth and less painful to bivalve. The feet, or arms, of these creatures are connected to their heads, not their bodies. The rest of the body is in front of the head. The cephalopods appear to be very different from other mollusks, but physiologically they are similar. Cephalopods, like most mollusks, have a mantle, a mantle cavity, a radula, and a U-shaped digestive tract.
Cephalopods have two kidneys and three hearts, which pump blue blood.
They are carnivores that feed on fish, shrimp, crabs and other cephalopods. A bite from a Blue-Ringed octopus, found in the South Pacific, is almost always fatal to humans. However, it takes a lot of provocation to get any octopus to bite a person. The most obvious difference between most cephalopods and other mollusks is the apparent lack of a shell. Octopuses do not have shells at all, while squids have a small internal shell.