The octopus is compared to the jellyfish, which has no brain or heart.

The jellyfish belongs to the phylum Coelenterata, has no skeleton, has a soft body, is usually transparent or light blue, and can be seen in the center of the body has a transparent round "umbrella cover", surrounded by many tentacles. Jellyfish rely on the flow of seawater to move, but also through the contraction of the body's muscles to move, but also can use the tentacles to catch prey, most of the jellyfish to the plankton for food.

Jellyfish have a relatively simple nervous system, with no real brain or central nervous system. It can only sense stimuli such as light, chemicals and temperature through neurons distributed in various parts of the body, thus controlling the jellyfish's movements and reactions. They also have floating iron-thirsty red blood cells in their bodies that can perform some heart-like functions.

Jellyfish Lifestyle:

Jellyfish are all carnivorous, feeding on plankton, small crustaceans, polychaetes and even small fish. Although jellyfish are beautiful and gentle, they are in fact very ferocious. Because jellyfish do not have respiratory organs and circulatory system, only primitive digestive organs, so the captured food is immediately digested and absorbed in the cavernous intestine.

The jellyfish is shaped exactly like a condensation, it is reddish-purple in color, no mouth, eyes. It has objects under its belly to which shrimp attach to swallow saliva. Most of them live only a few weeks or months, but some live to about a year, and some deep-sea jellyfish can live a little longer. When a jellyfish tries to sink in the water, its tentacles are extended and upward in long lines; when it intends to rise or move in a certain direction, the distal ends of the tentacles are bent against the direction of movement. Jellyfish use their tentacles to effectively change the direction of movement.