in a closed environment...these sound nasty....
" Hydrozoa are the least familiar of the four classes because most species are small. In their complex life cycle they alternate between two types of body plan. In the asexual fase it consists of a tubular body that is connected to the substratum at the lower end and bears a ring of tentacles around the mouth at the opposite end. These types of individuals are called polyps. They asexually bud off the second stage wich resemble a miniature jellyfish and is called a medusa. They are umbrella-shaped with a pulsing bell that propels them forward, on through the water,and a central trailing malibrum that carries the mouth below the bell. Medusa are the sexual fase in the life cycle of the hydrozoa. They produce sperm and ovaries (eggs) that fuse to create planktonic larvae. Ultimately these setle and give rise to polyps. A few species have solitary polyps, but in most cases the polyps devide repeatedly to form whole colonies often featherlike in appearance. An extreme example of the division of labour in a colony occurs in the bluebottle: One individual forms the float, others serve as defensive, stinging tentacles, others are for digestion and some solely engage in reproduction."