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.
For most mollusk, their shell is external including snails, scallops, oysters, clams and mussels. For other mollusk, like squid, and cuttlefish, they have a internal skeleton similarly to a shell. There are also some that do not have a shell at all, like octopus and slugs, with only a mantle for protection of organs.ollusks have a body without a cavity, has more than two layers of cell layers, tissues and organs. Mollusks are soft bodied animals with three main regions: head, visceral mass, and foot. The head of the mollusk contains the sense organs such as the brain. It has a pair of eyes, a mouth, sensory and nervous structures.