• Octopus is popularly known as devil-fish.

• Body is globose and bag-like with large head and trunk region.

• Head bears a pair of eyes and eight elongated equal arms webbed at the base which surrounded the month.

• Each arm bears suckers arranged in two rows. Suckers are sessile and large.

• Shell is absent.

• Mantle encloses the mantle cavity and the visceral mass.

• Octopus produces inky-fluid, which diffuses in water and forms a smoky screen for defence from the enemies.