Characteristics :

  • Have jointed legs
  • Have three or more pairs of mouthpars, including hard mandibles that hold, cut and crush food
  • Have two pair of antennae, or feelers, on head that function as sense organs
  • Have eyes with many lenses and are called compound eyes
  • Body has three main sections: head, thorax or trunk, and abdomen; in some, such as the crayfish, the head and thorax are fused into a cephalothorax
  • Have a brittle, external skeleton called an exoskeleton that completely covers the body and is shed periodically, even during the adult stage
  • Heart pumps circulating fluid through an open circulatory system, mean that the fluid is not always contained within tubes
Classification of the crustaceans is undergoing some restructuring. Listed below is a possible system of classification for these organisms. 
  • Kingdom: Animalia
    • ​Phylum: Cindaria
      • Class: Anthozoa (coral, anemones, others), Cubozoa (box jellies), Hydrozoa (hydras, fire corals, others), Scyphozoa (jellyfish)
Student Challenge:
  • Cnidarians typically go through two developmental stages, each with a body form that looks different from the other. These two body forms are calle polyp and medusa. How does each shape help it survive in its ecological niche?