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. Ink may also interfere with chemical receptors of predator. Octopus eats crab and other arthropods and kills with poisonous salivary secretion. Octopi used to study learning and memory, intelligent. Bilateral symmetry and tube body Body wall and internal organs segmented.