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.
Â© Jonathan Bird/ORG. For educational use only. There are over 50,000 known species of Mollusks, which makes them second only to the Arthropods in invertebrate phylum size. Among the Mollusks are some of the most well known of invertebrate sea creatures, like snails, clams, mussels, squid, and octopods.Although one might not see an obvious physical relationship between a snail and a squid, they are remarkably similar in construction.n general, mollusks have 3 body regions: a head, a visceral mass, and a foot.. The head contains the sense organs and brain, while the visceral mass contains the internal organs. The foot is the muscular lower part of the body which is in contact with the substrate.