The way jellyfish move is by shrinking the outer shell and squeezing the inner cavity.

The jellyfish changes the volume of the inner cavity by shrinking the outer shell and squeezing the inner cavity, and sprays out the water in the cavity. , moves by water jet propulsion.

The muscle fibers in the jellyfish epidermis extending from the top to the end of the umbrella control the contraction and expansion of the inner cavity. The inner cavity expands, and the water is slowly sucked in, filling the inner cavity; the inner cavity contracts rapidly, squeezing the water out of the cavity, and the thrust generated by the water spray makes the jellyfish move along the axial direction of the body.

When a jellyfish attempts to sink in the water, its tentacles extend upward in a long line shape; when it attempts to rise or move in a certain direction, the distal end of the tentacles bends against the direction of movement. Jellyfish use their tentacles to effectively change the direction of movement.

The bell-shaped body of some jellyfish has a special gland that emits carbon monoxide, causing the bell-shaped body to expand. When a jellyfish encounters a predator or encounters a big storm, it will automatically release its gas and sink to the bottom of the sea. When the sea is calm, it only takes a few minutes for it to produce gas to expand and float. In addition, some jellyfish umbrellas have air bags on the top. These jellyfish control the amount of inflation in each air bag and can also change the direction of the jellyfish's movement.