Hydra belongs to the phylum Colenterata and the class hydrozoa.

There are over 2,700 species of animals in this class, most of which live in the ocean. Included are certain varieties of jellyfish, such as the Portuguese Man’O War and the By-The-Wind-Sailor (Velella).

The fresh water Hydra are common and found in ponds, lakes and streams throughout the world. They are about 5 mm (1/4″) long and consist of about 100,000 cells. The Hydra is unique in many ways. Its body is composed of only two layers and has only seven different kinds of cells.

It captures food with its stinging tentacles and swallows it whole through a mouth located at the center of the tentacles. The Hydra feeds on Daphnia an ostracods and reproduces by budding. The green Hydra harbors algae within its body as a symbiotic relationship.

Hydra are readily available from science supply companies.