Box jellyfish (class Cubozoa) are cnidarian invertebrates distinguished by their cube-shaped medusae. This organism has a benthic polyp stage before developing into a pelagic adult medusae. They have cube-shaped, transparent medusae and are heavily-armed with venomous nematocysts. The medusae of hydrozoans are smaller than those of typical jellyfish, ranging from in diameter. Some have no polyp stages and some (e.g. "hydra") have no medusae. Hydrozoan polyps only bud, while the medusae of some hydrozoans can divide down the middle. This leads to a condition called Caput medusae. Dilation of this particular portacaval anastomosis results in what is referred to as caput medusae. Most hydrozoan medusae have just four tentacles, although a number of exceptions exist. Mars comes from the Medusae Fossae Formation. The medusae are either male or female. Adult medusae can have diameters up to . In medusae the only supporting structure is the mesoglea. Instead, these species rely on their medusae to extend their ranges. These are bell-shaped medusae specialised for locomotion.