Craspedacusta sowerbii is a freshwater jellyfish in the phylum Cnidaria. Since it is classified as a hydrozoan, it is one of many jellyfish that are also known as hydromedusae. Hydromedusan jellyfish differ from scyphozoan jellyfish because they have a muscular, shelf-like structure called a velum on the ventral surface, attached to the bell margin. Originally from the Yangtze basin in China, C. sowerbii is an invasive species now found throughout the world in bodies of fresh water.