Harpactopoid Copapod:

• first antennae short (5-9 segments, rarely beyond cephalothorax)
• Slight body taper

Cyclopoid Copapod

• First antennae 6-17 segments, rarely extending beyond prosome

Calanoid Copapod

• 1st antennae very long, 23-25 segments, may be beyond urosome

Malacostroca-Eucarida-Decapoda (includes largest crustacean group and largest living arthropods)

• Crayfish, shrimp and relatives
• Carapace (encloses bronchial chamber)
• thoracic appendages 1-3 maxillipeds
• mandible, 2 pair maxillae, 3 pair maxilliped
• 1 pair cheliped, 4 pair walking legs
• pleopods, uropods and telson

Malacostraca-Pericarida-Isopoda

• flattened dorsoventrally
• 7 pairs walking legs
• Abdominal gills and heart

Malacostraca-Pericarida-Amphipoda

• Laterally compressed
• 2 pairs gnathopods
• 5 pairs walking legs
• thoracic gills and heart