Water comes in by incurrent siphon, moves over gills. Gills are covered with mucus that traps bits of food. Food is moved by cilia to mouth. Most have 2 separate sexes, with sperm shed into water, enters female and fertilizes eggs in mantle cavity. Young develop in female.
Tentacles have suckers to hold prey.
Mantle is thick and muscular, with a funnel-like siphon Move by jet propulsion, filling cavity with water, then ejecting it out siphon. Chromatophores are cells with pigment granules. By expanding and contract cells, octopus, etc. have mottled appearance that lets them blend into background. Ink sac has thick, black liquid. When whale or moray tries to eat squid, etc., ink clouds water and squid swims away.