Members of class branchiopoda are small crustaceans that sometimes have a shield or bivalve-like carapace. They are typically found in fresh-water or brackish environments where they filter feed, eat detritus or prey on smaller animals.
Sources:
Tasch, P. 1969. Branchiopoda, in R. C. Moore ed., Treatise on Invertebrate Paleontology, Part R, Arthropoda 4, Volume 1. The University of Kansas and Geological Society of America. 128-191 pp.