The bulk of animals in this group are mollusks and crustaceans (insects are also considered animals but are such a large group that they are considered in a separate submodule).
Mollusks - these are soft-bodied organisms that commonly have a protective shell. They are found primarily in marine or moist environments. Invasive mollusks are generally introduced through human activity. They commonly cause a decrease in native mollusk populations, and their overgrowth can disrupt important waterways. Examples include the zebra mussel (Dreissena polymorpha) that has invaded the Great Lakes region, and the New Zealand mudsnail (Potamopyrgus antipodarum) that has invaded waterways in the western U.S.
Crustaceans - a member of a larger group called Arthropods. This group includes animals such as lobster, shrimp, and crabs. Crustaceans are mostly found in marine or freshwater environments, although there are a few terrestrial examples. Their primary pathway for introduction is human activity, such as aquaculture. Examples include the European green crab (Carcinus maenas) and the red blue crab, or Bocourt's swimming crab (Callinectes bocourti) found in southwest Florida.
