Water flea (Daphnia)

Daphnia are small, planktonic crustaceans, between .2 and 5 mm in length. Daphnia are one of the several small aquatic crustaceans commonly called water fleas because of their saltatory swimming style. They live in various aquatic environments ranging from acidic swamps to freshwater lakes, ponds, streams and rivers.

Daphnia as an aquarium shrimp ?

Amano shrimp (Caridina multidentata)

This aquarium shrimp was previously known as Caridina japonica but was renamed Caridina multidentata following a study in 2006. They are usually used in an aquarium because they are known as algae eaters, thus cleaning the aquarium if in large numbers.  

Red Cherry Shrimp (Neocaridina heteropoda)

These aquarium shrimp are primarily algae eaters. They will eat any food intended for aquarium use, but some will prefer compressed algae discs. 

Snowball Shrimp (Neocaridina cf. zhangjiajiensis var. white)

This aquarium shrimp is one of the most beautiful species of shrimp in the hobby. Its pure white coloration, including the eggs, are what really set this species apart from the rest. The Snowball Shrimp was named after the color of its eggs, which look like snowballs. They are also known as algae eaters like the rest of Neocaridina family.

Cray fish

Cray fish, crawfish, or crawdads are freshwater crustaceans resembling small lobsters, to which they are closely related. Pet crayfish are kept in freshwater aquariums, their disposition towards eating almost anything will also cause them to consume most aquarium plants in a fish tank.