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The Cubomedusae, variously known as the box jellies, sea wasps, or fire medusae, comprise the Cnidarian class Cubozoa. The Cubomedusae were formerly considered to be an order in the Scyphozoa. Now they are considered their own class and comprise two orders, the Carybdeida and the Chirodropida. The group includes about 48 species found in tropical and subtropical latitudes.

Bells of the Cubomedusae are indeed cuboidal, with four flattened sides that are square when viewed from the exumbrellar side or in transverse section (Figure 3.14a). The bell has a simple margin that bends inward to form a velarium (Figure 3.14b). Tentacles arise from the four corners of the bell, either singly or in groups. The base of the tentacle(s), the pedalium, is a blade‐like structure that gives rise to a single tentacle in the family Carybdeidae and a palmate structure that gives rise to several tentacles in the family Chirodropidae (Figure 3.14c and d). Below the pedalium, the tentacle is hollow and armed with rings of nematocysts.

A four‐sided manubrium leads to a simple, central stomach that is located at the apex of the sub‐umbrellar surface. The stomach differentiates into four gastric pockets that occupy the flattened sides of the umbrella.

The life history of the Cubomedusae is much like that of the hydromedusae and scyphomedusae with one important difference: the polypoid stage of the Cubomedusa does not strobilate. Rather, each polyp metamorphoses into an individual medusa. Arneson and Cutress (1976) described the development of Carybdea alata in Puerto Rican waters as proceeding from a released blastula stage to a swimming planula in 1 day, settlement of the planula in an additional 4 days, growth and maturation of the polyp for about 60 days, and the metamorphosis culminating in a liberated medusa taking an additional week, for a total of about 75 days for the entire process. Temperature during development was 26–29 °C.

Genera include: Carybdea, Tripedalia, Tamoya, Chirodropus, Chiropsalmis, and Chironex.