Craspedacusta sowerbyi Lankester, 1889 (Limnomedusae, Oliandisidae), reaching diameters of 2-3 cm, is one of the few freshwater medusae. It occurs now on all continents, except Antarctica. Its polyp stage is probably more widespread, but due to its small size of 1 mm it is rarely detected. The medusa develop only under special conditions, one of them being that the water temperature must be above 25 °C over a certain period.