"Physalia" is not a single animal: it is a siphonophore. This is a colony of four kinds of zooids. Zooids are very small, highly modified individuals. These zooids are specialized polyps and medusoids. Though structurally similar to other cnidarians, the zooids do not live by themselves: they are attached to each other. Each type of zooid does not have some structure and functions. It depends for survival on the others doing what it cannot do by itself.