Jellyfish usually live a single, floating or swimming life. Few species are in groups, and some groups can live a fixed life. Jellyfish is bell-shaped or inverted bowl-shaped or umbrella-shaped. The convex surface is called the outer umbrella surface or the upper umbrella surface, and the concave surface is called the lower umbrella surface. There is a drooping tube in the center of the lower umbrella surface, called the handle, and its free end is the mouth. The edge of the umbrella has a circle of tentacles, and the edge of the jellyfish umbrella protrudes inward in a narrow sail shape. The jellyfish in the pot have no membrane. The body wall structure of jellyfish type is basically similar to that of hydra type, and it is also composed of two layers of epithelial muscle cells sandwiched between mesothelium, but the mesothelium of jellyfish type is far more developed than that of hydra type. The gastric circulation cavity surrounded by the body wall is also relatively developed, which is either a simple sac or divided into four gastric sacs by the membrane. Four (hydra jellyfish) or more (bowl jellyfish) radiation tubes extend from the gastric sacs to the umbrella rim, and are connected with annular tubes parallel to the umbrella rim. Centrifugal tubules can also extend from the umbrella rim. At the base of an umbrella or tentacle, there are sensory organs, such as eye points or foot sacs.