Which cnidarians can live in freshwater?

While most cnidarians are marine animals, some species inhabit freshwater environments. These include:1

• Hydras: These are small, hollow, cylindrical freshwater creatures belonging to the class Hydrozoa. They are among the simplest multicellular animals to possess muscle tissue.12
• Freshwater jellyfish: This term refers to the medusoid (free-swimming) form of the genus Craspedacusta, which also belongs to the class Hydrozoa. The species Craspedacusta sowerbyi is widespread in the freshwaters of the Northern Hemisphere. It is important to note that these are not true jellyfish, as true jellyfish belong to the class Scyphozoa and are exclusively marine.3