well... the pipefish have like two flaps of skin, and the female produces the eggs and places a long string of eggs in the middle of these flaps, and then the male folds the flap together, continue till the end of the gestation period... Know all cnidarians are polyps at some time in their life... I'll just talk about those that end up as "jellyfish"... the children are free FLOATING , then when they land, they grow for a while, and this is when they are polyps, then when they reach a certain age, they detach from wherever they were attached , and they become free SWIMING, this is called the medusa, when they mate, the females release the eggs into the water, and the males release the sperm, these --- cells meet somewhere in the water column, where they mature into the free FLOATING stage,...