Hydra are tiny animals closely related to jellyfish. They are a carnivorous species that can be found in healthy freshwater rivers and streams where they attach themselves to plants and rocks.

Hydra have a sack-shaped body with a ring of tentacles around the mouth at the top. They use those tentacles, covered with paralyzing nematocysts, to trap small cruscaceans, stun them and bring them into the mouth where they are digested.