Dark field light micrograph of a Hydra sp. organism. Hydra are small, freshwater cnidarians that are closely related to jellyfish and sea anemones. They have a hollow, tube-like body with a crown of tentacles surrounding their mouth, which they use to capture prey. These organisms are particularly interesting due to their remarkable regenerative abilities and their apparent immortality. Magnification: 45x when printed 10 centimetres wide.