Octopus are soft-bodied, eight-limbed mollusks of the order Octopoda. The order consists of 300 species and is grouped within the class Cephalopoda with squids, cuttlefish, and nautiloids. Like other cephalopods, an octopus is bilaterally symmetric with two eyes and a beaked mouth at the center point of the eight limbs. However, the soft body can radically alter its shape, enabling octopuses to squeeze through small gaps. They trail their eight appendages behind them as they swim. The siphon is used both for respiration and for locomotion by expelling a jet of water. Octopuses have a complex nervous system and excellent sight and are among the most intelligent and behaviorally diverse invertebrates.

Octopus is eaten in many cultures, such as on the Mediterranean and Asian coasts. The arms and other body parts are prepared in various ways, often varying by species or geography. Live octopuses are eaten in several countries around the world, including the US.

Shellfish

Shellfish is a colloquial and fisheries term for exoskeleton-bearing aquatic invertebrates used as food, including various species of mollusks, crustaceans, and echinoderms. 

Although most kinds of shellfish are harvested from saltwater environments, some are found in freshwater. Shellfish are among the most common food allergens.