Octopuses have a pouch-shaped body and eight powerful arms (not tentacles), usually with two rows of suction discs on each. They don't have any bones, but in some cases, the brain may be enclosed in cartilage. Their size can range from 1.5 cm (0.6 in.) to more than 5 m (16 ft.); spans of up to 9 m (30 ft.) have been recorded, although these measurements are often considered questionable. The arms usually make up about half their span.
The octopus (cephalopod) is a mollusk having no shell, eight muscular arms or tentacles, a pouch-shaped body, and two large, highly developed eyes. The prey (crabs, lobsters, and other shellfish) is seized by the sucker-bearing arms and pulled into the web of tissue at the base of the arms, paralyzed and partially digested by a poisonous salivary secretion, and chewed by the horny, beaklike jaws and the radula, or tooth ribbon. Octopuses move by pulling themselves along with their arms or by forcibly expelling water through the funnel or siphon in the manner of their near relative, the squid. Sometimes they construct barricades of large stones; most hide in rocky crevices at the approach of danger or cloud the water by ejecting dark "ink" from the ink sac. They also change color (from pinkish to brown) according to mood and environment, sometimes exhibiting rapid waves of color changes that sweep over the body. The 3-ft (91-cm) American devilfish is found off Florida and in the West Indies; a smaller species that reaches only 2 in. (5 cm) is found N of Cape Cod. The common octopus of the Mediterranean and the Atlantic occasionally reaches 10 ft (3 m) in length; the giant octopus of the Pacific may have a diameter of over 30 ft (9 m). Octopuses reproduce sexually. One of the arms of the male is modified into a sexual organ that deposits spermatophores in the mantle cavity of the female. The eggs are encased in capsules and attached to a rock, where the female guards them. The young hatch directly, without a larval stage. Octopus is eaten in many parts of the world.