Jellyfish swim by opening and closing a part of their body called the bell, which is the transparent, sack like part of their body that the tentacles hang from. The bell catches water when it opens and ejects it when it closes, propelling the jellyfish forward.
When jellyfish open and close their bell it is much like an umbrella being opened and closed. The bell has a ring of muscles around it, which allow it to constrict and relax. The bell makes up the body of the jellyfish, giving it shape and buoyancy. Jellyfish move vertically through the water, sinking and rising as the bell opens and closes. They are carried by the currents of the water, unable to steer themselves.
During storms or strong tides, jellyfish can be washed ashore, leaving them helplessly stranded. Due to their delicate nature, jellyfish tentacles are subject to being ripped off in rough waters. The tentacles of jellyfish hang from the bell and do not help them swim. Instead, they capture small animals on which jellyfish feast. There are stinging organs in the tentacles that stun prey as the jellyfish drifts by. The mouth of the jellyfish is located on the underside of the bell.