Hydra viridissima is a species of cnidarian and is the only green hydra found in Europe. Green hydra are typically 10mm long, and they have tentacles that are about half of their length. H. viridissima is often known as the green hydra, the species appears green because of the symbiotic relationship with Chlorella vulgaris, which is a green alga that lives within the organism. 

Good photographs are required to support records.

Hydra are normally sessile and live on aquatic vegetation they secrete mucous to attach using their basal disc. Commonly found in freshwater, mostly ponds, rivers, and slow flowing parts of streams and rivers (because they are sessile they cannot be in fast current water).

All year round – hydra do not seem to age, but may die of things like disease or starvation.

Typically they feed on small crustaceans, insects and annelids.

True status in Britain is difficult to determine due to lack of records.

Status in Leicestershire and Rutland not known.