Cypris are ostracods (a type of crustacean) and related to mussels and shrimp. They are small, about 1/2 – 2mm long, with a hard outer shell. In freshwater ponds they are usually found scuttling around among the debris at the shallow edges. They swim smoothly with appendages extended from between the two halves of their carapace (shell). When disturbed, they withdraw their limbs into their shell and clamp the halves tightly together.