Jellyfish, any planktonic marine member of the class Scyphozoa (phylum Cnidaria), a group of invertebrate animals composed of about 200 described species, or of the class Cubozoa (approximately 20 species). read more
Jellyfish: Cnidaria Appearance: Jellyfish are neither jelly nor fish. Jellyfish lack backbones, heart, blood, brain, or gills and, in fact, are over 95% water. read more