A hydra is a small, freshwater organism belonging to the phylum Cnidaria. It is known for its tubular body and tentacles that contain specialized cells called cnidocytes, which can sting and capture prey. Hydras are typically found in ponds and streams, where they attach themselves to surfaces using a structure called a basal disc. One of the most fascinating features of hydras is their ability to regenerate. If a hydra is cut into pieces, each piece can grow into a new hydra. This remarkable regeneration ability has made hydras a subject of scientific research, particularly in the study of stem cells and aging.