How do gelatinous animals swim?
Among the advantages of the gelatinous lifestyle is built-in buoyancy. With tissue that lacks bone and dense muscles, and is at least 95% water, jellies have about the same density as water. They lack accessory buoyancy structures like the swimbladders of fish, and don’t need to expend a lot of energy in swimming to keep from sinking. Jellies also can be carried relatively passively over long distances by oceanic currents. Nevertheless, jellies and other gelatinous animals do possess decent swimming capabilities using a variety of mechanisms. Cnidarian jellies utilize coronal (circular) muscle fibers in the subumbrella of the bell (the “bottom” of the bell). By contracting these muscles, water is pushed out, which propels the jelly forward. Jellies vary in the frequency and power of the bell pulsing, with some having very rapid, jerky pulsing and others possessing a more gentle, slow-motion style of swimming. The frequency of pulsing is under some nervous control. The margin of the bel
