The hydra freshwater polyp moves by attaching its tentacles to an object, then dragging itself or rolling in a cartwheel motion to its new location, usually a stick or leaf that has been submerged. It can also detach from its base to float freely on an air bubble for longer distance travel.
The educational website Biology Corner says hydras are a type of cnidarians, a phylum of tentacled, stinging water-dwelling life forms that includes sea anemones and jellyfish. The hydra lives in freshwater ponds, eating tiny organisms like brine shrimp that come a little too close to the tentacles. It grows up to a half-inch in length, but it only grows when it is attached to a plant or the pond bottom. Some hydras reproduce asexually through budding, while other hydras produce eggs or sperm. Fertilized eggs fall to the lake bottom, where they lie dormant until conditions are appropriate for hatching.
While hydras are very simple life forms, they are of particular interest to biologists because they do not seem to age or to die of age, and they can regenerate damaged parts. Upon close study, it appears that their stem cells are able to renew themselves indefinitely instead of shutting off like stem cells in higher organisms.