Scyphozoan

noun

1. Any of various marine cnidarians of the class Scyphozoa, which includes most of the jellyfishes, characterized by the absence of a polyp stage or by a polyp that is extremely small.
2. Any true jellyfish of the class Scyphozoa
3. any of various usually free-swimming marine coelenterates having a gelatinous medusoid stage as the dominant phase of its life cycle