What is hydra are considered to be ___.?

Hydra are considered to be a type of freshwater cnidarians, which are simple, multicellular organisms that belong to the phylum Cnidaria. They are radially symmetrical with a sac-like body and tentacles that surround a central mouth. Hydra are predatory and use their tentacles to capture small prey such as water fleas, insect larvae, and crustaceans. They have a unique ability to regenerate and can regrow body parts, even if torn into pieces. Hydra are found in freshwater environments all over the world, including ponds, lakes, and rivers. They are also commonly used in scientific research as a model organism for studying regeneration and aging.