Is there such a thing as a freshwater jellyfish?

Yes, but… the freshwater “jellyfish” is not a true jellyfish as are some of its marine relatives. Freshwater “jellyfish” differ slightly from the true marine jellyfish. Craspedacusta sowerbii (kras-ped-uh-kus-tuh) is the scientific name of this freshwater “jellyfish”.

One obvious difference is that unlike marine jellyfish, C. sowerbii has a structure called a velum on the ventral surface. This thin, shelf-like membranous structure extends inward from the circular edge (ring canal) of the bell. The manubrium, which ends in a mouth, extends down through a hole in the velum. The velum helps set C. sowerbii apart from the true jellyfish. However, because C. sowerbii looks like a jellyfish, we call it a jellyfish!

C. sowerbii belongs to the class Hydrozoa which includes the more common hydra.