The word "Hydra" was applied to a variety of large, poisonous, snake-like creatures.
One Hydra was a creature that dragged itself across the ground. It had a bulbous body and three eyes, one looking forward, the other two on the sides. Inside the Citadel, Captain Richard Haliwell and Emily Boyes-Dennison were forced to face one of these during one of their tests for survival. Haliwell managed to blind the creature using his cutlass. (PROSE: Imperial Moon)