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.
Mollusks. Maybe you think that snails, clams, mussels, squid, and octopods are very different. Yet, they are all in the same category of animals known as mollusks and are structurally similar. Mollusks are some of the most well known of invertebrate sea creatures (there are over 50,000 species). Some are very rare and are only found in very deep-water. Mollusks have three body regions. 1. The head contains the brain and the sense organs. 2. The visceral mass contains the internal organs. 3. The foot is the muscular part of the body. Mollusks usually, but not always, have a shell, which is secreted by a body wall called the mantle. Many mollusks have a tongue of sorts, called a radula. The radula is rough like sandpaper. Mollusks have well developed body organs that are used in the respiratory, circulatory and nervous systems. The Stomach-Foot The stomach-foots (class Gastropoda) contains about 70% of all mollusk species.