2. Octopus, also known as octopus, is a mollusk, which evolved from cephalopod mollusk. Generally, the body is very small, and the eight tentacles are thin and long, so it is also called "Octopus".
3. Octopus is the "overlord" in the ocean. It is extremely powerful, cruel and resourceful, and many marine animals are afraid of it. Octopus is a sensitive animal, and its nervous system is the most complex and advanced among invertebrates, including central nerve and peripheral nerve, and auditory nerve, olfactory nerve and visual nerve are divided in the cerebral ganglion. The most developed of its sensory organs is the eye, which is not only big, but also bulging and motionless. The structure of the eye is very complicated, with a cornea in front, a sclera around it, and a well-developed lens comparable to that of vertebrates. In addition, there is a small nest in the skin behind the eyes, which is specially used for smell.