It is modified to form a funnel, through which water is expelled from the mantle cavity. This sort of jet propulsion results in very fast locomotion in some species. Around their mouths, cephalopods have a ring of tentacles that bear powerful suckers in some species. The tentacles are used to search out and grasp food. Most cephalopods have chromatophores, special pigment cells, in their skins, which allow them to change color rapidly.
Cephalopods have the most complex brain of any invertebrate.
Most species also have excellent eyes that are astonishingly similar to those of vertebrates. Most species have a single pair of gills, a mostly-closed circulatory system, and accessory or branchial hearts. The gills are ventilated by the muscular action of the mantle wall. Cephalopods are dioecious. Fertilized eggs are attached to the substrate and are sometimes tended by the female.