Crustaceans (Class Crustacea) is a large class of mostly aquatic animals. Although many species are marine, there is a large number of small freshwater species and a few species of larger freshwater crayfish. There are many subdivisions to the Crustacea including such diverse animals as water fleas, fish lice, barnacles, crabs, shrimp, and crayfish.

Jointed Legged Animals (Phylum Arthropoda) make up the largest phylum. There are probably more than one million different species of arthropods known to science. It is also the most successful animal phylum in terms of the total number of living organisms.

Butterflies, beetles, grasshoppers, various insects, spiders, and crabs are well-known arthropods.

The phylum is usually broken into the following five main classes:

   Arachnida:      Spiders and Scorpions
   Crustacea:      Crabs and Crayfish
   Chilopoda:      Centipedes
   Diplopoda:      Millipedes
   Insecta:        Insects

There are several other "rare" classes in the arthropods that should be mentioned. A more formal list is as follows:

   Sub Phylum Chelicerata

     C. Arachnida:      Spiders and scorpions
     C. Pycnogonida:    Sea spiders (500 species)
     C. Merostomata:    Mostly fossil species

   Sub Phylum Mandibulata

     C. Crustacea:      Crabs and crayfish
      
   Myriapod Group

     C. Chilopoda:      Centipedes
     C. Diplopoda:      Millipedes
     C. Pauropoda:      Tiny millipede-like
     C. Symphyla:       Garden centipedes

   Insect Group

     C. Insecta:        Insects

The above list does not include some extinct classes of Arthropods such as the Trilobites.

Animal Kingdom contains numerous organisms that feed on other animals or plants. Included in the animal kingdom are the lower marine invertebrates such as sponges and corals, the jointed legged animals such as insects and spiders, and the backboned animals such as fish, amphibians, reptiles, birds, and mammals.