Presently containing roughly 40 valid species, Cubozoa is the most species-poor class of the phylum Cnidaria. The first cubozoan was described more than 350 years ago by Linnaeus. Having distinctive features, it is not surprising that as additional species were discovered they have nearly always been classified together, usually in the taxon Cubomedusae. In the 1970s, they were elevated into the distinct class Cubozoa, after it was recognized that the polyps and life cycle were rather distinct from those of Scyphozoa, in which cubozoan species had been previously classified.
Few tests of cubozoan monophyly have been conducted, but its members are distinctive. They all have four perradial sensory rhopalia containing strikingly complex eyes with ocelli, vitreous bodies, lenses, and retinas, as well as statocysts. In addition, all cubozoans possess a piece of tissue entirely of subumbrellar origin, known as the velarium, which serves to narrow the ubumbrellar opening for jet propulsion. The velarium contains canals and is supported by structures known as frenulae. The tentacles of cubomedusae have thickened muscular bases termed pedalia and are concentrated at the four interradial corners.