Octopus, also known as Octopus, is a marine mollusk.

A general term for cephalopod mollusks of Octopoda. But strictly speaking, it only refers to Octopus, which is widely distributed in shallow water.

Octopuses vary greatly in size. The smallest octopus is the tree octopus (O. arborescens), which is about 5 cm (2 inches) long, while the largest species can reach 5.4 meters (18 feet) and its wrist span can reach 9 meters (30 feet). A typical octopus has a cystic body; The boundary between the head and the body is not obvious, with large compound eyes and 8 retractable wrists. Each wrist has two rows of fleshy suckers, which can strongly hold other things. The base of the wrist is connected with a webbed tissue called a skirt, and its center has a mouth. There are a pair of sharp horny palates and file-like toothed tongues in the mouth, which are used to drill through shells and scrape their meat.

Octopus sucks water into the mantle, breathes it and excretes it through a short funnel-shaped body tube. Most octopuses crawl along the bottom with suction cups, but when they are frightened, they will spray water from the body tube, thus moving quickly in the opposite direction. When in danger, ink-like substances will be ejected as a smoke screen. Some kinds of substances can paralyze the attacker's sensory organs.

The most well-known octopus is the common octopus (O. vulgaris), which is of medium size and widely distributed in tropical and temperate waters all over the world. It lives in caves or crevices on the rocky seabed and can't hide its joy. They mainly feed on crabs and other crustaceans. This species is considered to be the most intelligent invertebrate, and it has highly developed cells containing pigments, so it can change its body color very quickly, which is also surprising.

Octopus is dioecious. The male body has a specialized wrist, called the stem wrist or the cross wrist, which is used to put the sperm bag directly into the female body's coat cavity. Common octopus mates in winter. Eggs are about 0.3 cm (1/8 inch) long, and the total number is more than100000, and they are produced under rocks or in caves. Larvae at 4? Hatched after 8 weeks, during the incubation period, the female guards beside the egg, cleans the egg with a sucker, and stirs the egg with water. Young octopus looks like an adult and is small. After hatching, it needs to drift with plankton for several weeks, and then sink to the bottom of the water for concealment.

Octopus mainly feeds on shrimps and crabs, but some species eat plankton. Many marine fish feed on octopus. In the Mediterranean region, eastern countries and some other parts of the world, octopus has long been regarded as a delicacy.