The English popular name jellyfish has been in use since 1796
Jellyfish and generally transparent or translucent, free-swimming
jellyfish are not vertebrates, let alone true fish, the word jellyfish is considered by some to be a misnomer. Public aquariums may use the terms jellies or sea jellies instead. The term "jellies" has become more popular than "jellyfish".
In scientific literature, "jelly" and "jellyfish" are often used interchangeably.
Monterey Bay Aquarium Jellyfish
http://vimeo.com/17748447
Feb 4th 07:15