Hydra

Hydra, genus of freshwater animal of the phylum Coelenterata, perhaps the most familiar of the class Hydrozoa. The hydra is found in ponds, lakes, and streams throughout the world. The body is an elongated 2-in (2.5-cm) column with a mouth at one end surrounded by tentacles. Normally attached by the other end to the substrate, hydras can move by “looping” across a plane surface or by free-swimming. Hydras reproduce by asexual budding when food is abundant. When food is scarce, ovaries and testes develop on the column, and sexual reproduction gives rise to resistant, dormant embryos.