The term 'water flea' is used to describe a small aquatic organism known as Daphnid, which has seven letters. It is a type of CRUSTACEAN, which has ten letters. Water fleas are small, planktonic organisms that belong to the class of Crustacea, and are found in both freshwater and marine environments. They are an important part of the food chain, providing food for many species of fish, amphibians, and other aquatic animals.