Historical reference: Do not rely on this information. It is very old. About this collection
Branchiopoda (i.e. gill-footed), a subdivision of the Entomostraca, including the Cladocera, Phyllopoda, and Trilobita; the characters possessed in common by these three orders are that the gills are borne on the legs, and that some at least of the legs are flattened out to serve as gills.