FRESHWATER STINGING ANIMALS ( CNIDARIA)
In contrast to the marine species, there are very few freshwater hydroids. The two stalked species of hydra - Hydra viridis Linnaeus and H. oligactis Pallas, green and brown respectively - are widespread in Britain, including Cornwall. There are four other European species, none of which have been recorded in Cornwall, and all of which are stalkless. The fifth European hydroid, Cordylophora lacustris Allman, is branched and can live in fresh or brackish water: it is said to be “rather local and scarce” (Fitter & Manuel, 1994) and has been found in the Tamar at Calstock.