The Collaborative International Dictionary
Swimming bell
Swimming \Swim"ming\, a.
That swims; capable of swimming; adapted to, or used in, swimming; as, a swimming bird; a swimming motion.
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Suffused with moisture; as, swimming eyes.
Swimming bell (Zo["o]l.), a nectocalyx. See Illust. under Siphonophora.
Swimming crab (Zo["o]l.), any one of numerous species of marine crabs, as those of the family Protunid[ae], which have some of the joints of one or more pairs of legs flattened so as to serve as fins.
Wiktionary
swimming bell
n. The bell-shaped part of a jellyfish (and similar organism) that generates locomotion by pulsate