1. (used with a sing. verb) A theory that explains the global distribution of geological phenomena such as seismicity, volcanism, continental drift, and mountain building in terms of the formation, destruction, movement, and interaction of the earth's lithospheric plates. 2. (used with a sing. or pl. verb) The dynamics of plate movement.
Despite the fact that mollusks are very susceptible to changes in their environment because of their permeable skin and soft body (often with an exoskeleton in the form of a shell), they have adapted to all of the main environments of our planetâmarine, freshwater, and terrestrial. With 41% of the 736 documented extinctions of all animal species, the number of mollusks exceeds that of any other major taxonomic group 3. 2  Most documented endangered mollusk species are non marine (they live in freshwater or terrestrial environments) 5.
The most common examples for mollusks include snails, clams and squids. All mollusks have a thin outer layer called the mantle, which surrounds the body organs located insides the visceral mass. Mantle secretes the protective shell of the body. Gas exchange is taken place in gills.Mollusks have an open circulatory system in which the heart pumps blood into the open space around the body organs. They have a prominent head with a mouth and sensory organs. Mollusks like snails have a well-developed muscular foot for movement and adhesion.as exchange is taken place in gills. Mollusks have an open circulatory system in which the heart pumps blood into the open space around the body organs. They have a prominent head with a mouth and sensory organs. Mollusks like snails have a well-developed muscular foot for movement and adhesion.