• 1) Respiratory adaptations depend upon the type of environment:

  a) aquatic: book gills occur in primitive aquatic chelicerates (horseshoe crabs); gills in crustaceans are typically exopodites or epipodites, and may be thoracic (most common) or abdominal; gills depend on some method for pumping water

  b) terrestrial: 1 or 2 pair of abdominal book lungs occur in many terrestrial arachnids; most uniramians, some arachnids and a few crustacea have spiracle/trachea systems; lungs/trachea depend upon diffusion that may be augmented by inspiration/exhalation

• 2) Arthropod coelom is greatly reduced (limited mainly to the gonads)

  a) arises embryologically via schizocoely

  b) most of the primary coelom fuses with the epineural sinus yielding an extensive hemocoel

• 3) Crustacean diversity

  a) 5 classes, 3 major (Branchiopoda, Maxillopoda, Malacostraca) and 2 minor (Remipedia, Cephalocarida)

  b) most are marine, but one class is primarily freshwater and three others have freshwater members

  c) most are free living, 2 classes have a number of parasitic species

  d) body size is generally small (<20mm) in most classes/subclasses, but large size (>100mm) occurs in three subclasses

  e) classes are distinguished by: number of tagmata, number of segments per tagmatum, number of anterior segments covered by a carapace, number of segments fused with the carapace, presence of movable projections (rami) from telson

  f) primitively, crustaceans were probably particle feeders; however the most successful class is mainly raptorial

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