Hydra are small polyps from 1 to 20 mm in body length. The body is crowned by up to 10 or 12 tentacles.

Can we see hydra with naked eyes?

Hydra are truly fascinating small aquatic animals. Most hydra are tiny, reaching a maximum of only about 30 mm long when fully extended. They are barely visible to the naked eye and a hand lens or microscope are needed to be able to see them properly.

How big is a freshwater hydra?

Hydra vulgaris, the fresh-water polyp, is a small animal freshwater hydroid with length from 10 mm to 30 mm and width about 1 mm.