Class CRUSTACEA.
Sub-class ENTOMOSTRACA.
Order Astracoda—Free. Body enclosed in a bivalve shell.
Order Copepoda—Free. Five pairs of feet adapted for swimming.
Order Cirripedia—Sessile. Enclosed in a shell of many valves.
Order Branchiopoda—Free. Gills attached to feet.
Sub-class MALACOSTRACA.
Division EDRIOPHTHALMATA, or Sessile-eyed Crustaceans.
Order Isopoda—Body flattened. Seven pairs of legs—equal.
Order Amphipoda—Body flattened laterally. Legs adapted for both walking and swimming.