The octopus is part of the phylum Mollusca; it has a very soft body with eight arms, or four pairs of arms. Each of its arms has two rows of suction cups and if it ever loses an arm the arm it lost will eventually grow back. They live and walk around the ocean floor on their tentacles. An Octopus also has a hard beak with its mouth centered on its arm.
The muscular system of the octopus permits it to move using jet propulsion thanks to three different types of muscles: longitudinal, circular, and radial. The inner skin of the octopus is composed of many layers of muscle, one on top of the other. These structures or muscles enable the various movements of the octopus by balancing and supporting one another. When the octopus flush out water the circular muscles contract in length, which increase their length. During this contraction, the longitudinal muscles stretch to prevent the elongation. In the meantime the radical muscles remain stretched that cause the mantle of the octopus to thicken and then the mantle cavity is filled with water again.