As Cnidaria they have stinging cells on their tentacles. They are hydrozoa, and belong to the same order as other polyps. Most "Hydra" are microscopic in size. Hydras can be found in almost any unpolluted body of water. Hydras reproduce by budding. In budding, the offspring forms as a lump on the parent and eventually becomes big enough to break off and live by itself. They can move if they need to by a kind of slow somersaulting motion. 