Portuguese men-of-war. Artwork of a group of Portuguese men-of-war (Physalia utriculus) in the open ocean. Each Portuguese man-of-war is not one organism, instead being a colony of hydrozoan animals. Members of the colony have distinct roles. One individual forms the float (seen here), which is filled with a mixture of nitrogen and carbon monoxide. Individuals called gastrozooids are responsible for digesting food and passing it to the rest of the colony. Prey is captured by dactylozooids, which comprises a large stinging tentacle. Reproduction is carried out by gonozooids. The colony is planktonic, being carried around by ocean currents.