More obvious in larval forms, adults have fused segments -----> Head | Thorax | Abdomen

Some have a fused head and thorax -- the cephalothorax


Subphylum Chelicerata



Subphylum Crustacea

  • Marine members include shrimp, lobster, barnacles, & crabs

  • Terrestrial crustaceans called isopods (pillbugs or rollypollys)

  • Freshwater members include crayfish and daphnia

  • All have mandibles for chewing or tearing

  • Have cephalothorax & abdomen

  • Lobsters and large custraceans are called Decapods
  • Barnacles are sessile (don't move)
  • Have 10 pairs of jointed appendages
  • Breathe through gills

Crayfish Dissection covers more on the Crayfish Anatomy



Subphylum Uniramia - Insects and their Relatives

Class Chilopoda

Class Diplopoda


Class Insecta

Insect Life Cycle

Metamorphosis - dramatic physical change

Complete metamorphosis: Larva --> pupa ---> adult (example: butterflies)
Incomplete metamorphosis: Egg --> nymph --> adult (example: crickets)


Social Insects: Honeybees (workers, queen, drones). Termites, some wasps

Queen: Lays eggs (1 queen per hive)
Drones: a few males to fertilize eggs
Workers: all infertile females