The American Heritage® Dictionary of the English Language, 4th Edition
n. Any of various marine coelenterates of the class Scyphozoa, which includes the large jellyfishes, characterized by the absence of a velum and by a polyp stage that is very small or lacking entirely.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
n. any of various usually free-swimming marine coelenterates having a gelatinous medusoid stage as the dominant phase of its life cycle
Word Usage
"Kuhn K, Streit B, Schierwater B (1999) Isolation of Hox genes from the scyphozoan Cassiopeia xamachana: implications for the early evolution of Hox genes."