Of ‘clams’ and water fleas! -

This unknown is so much like Daphnia, we decided to show both here. Many people guess this Mystery Organism as a species of Daphnia. Perhaps we fool our viewers by removing one of the two clam-like carapace plates - in this case, the left one, exposing a full view of the body of this beautiful Arthropod.

Clam shrimps belong to the Order Conchostraca, a group of crustaceans common in freshwater ponds, although not as common as Daphnia. Daphnia belongs to a closely related order, Order Cladocera. Daphnia lacks the hinged bivalve carapace of the clam shrimp, and its carapace is partially fused on the dorsal side at the bottom of the animal. Another distinguishing feature is the number of 'legs' or trunk appendages - 10 to 30 pairs in clam shrimp, but only 4-6 pairs in Daphnia and other Cladocerans.

Some clam shrimps live in seasonal ponds. As the pond dries out, the clam shrimp females lay eggs capable of surviving seasonal drought. In the spring, after these 'vernal pools' have filled with the winter rains, the clam shrimps once again hatch and develop into adults with the characteristic bivalve carapace. Some species grow up to 1.5 cm across!

For a concise and revealing teaching video about Arthropods, get our video/DVD: Branches On the Tree of Life: Arthropods. For a rich overview of freshwater biology, see our program: The Biology of Lakes Ponds and Wetlands.