Mollusks chitons

The three mineralized hard parts are the teeth of certain mollusks called chitons, the dentin component of vertebrate teeth, and the skeleton of the larvae of the sea urchin. They all possess very different material properties. Taxonomically they are also very different, with each being formed by organisms that belong to different phyla the Mollusca, the Chordata and the Echinodermata respectively. 

The largest number of species of mollusks are in the class Gastropoda, which includes snails with a coiled shell, and others lacking a shell. The next largest group are the bivalves (class Bivalvia), the chitons (class Am-phineura), and octopus and squid, (class Cephalopoda). The other classes of mollusks are the class Scaphopoda (consisting of a few species of small mollusks with a tapered, tubular shell) and the class Monoplacophora, a... 

Mollusks are complex invertebrates whose name literally means soft bodied. Even though all mollusks possess soft bodies, their outward appearances vary enormously, from small animals enclosed in two hard shells to large, eight-legged creatures that hide quietly among the rocks. Mollusks are subdivided into four groups based on their anatomy chitons, which are insectlike... 

Led by the work of Bergmann, the sterols of molluscs were recognized very early to be complex mixtures (71) which could not be resolved adequately at that time. More recent studies have confirmed the complexity of sterol composition of mollusks (81-83) and using liquid chromatography and gas chromatography, 17 sterols were identified in one species of scallop (82) and nearly forty were identified in the eastern oyster (83). These studies indicate that, except for the chitons which contain A -sterols (84), the sterols of molluscs are primarily A and may contain from 26 to 30 carbons. Although examinations of many mollusc species indicates that sterol biosynthesis from acetate occurs, it is sometimes slow (81). In the eastern oyster, the most frequently studied... 

The mollusks are divided into seven classes that are very rmequal in the number of species they contain. The Aplacophora are vermiform mollusks, generally of small size and present in all the world s oceans, but their chemistry does not seem to have been studied. The Monoplacophora were discovered in 1952 with the species Neopilina gaiathea they are currently represented only by about 15 species and are stiU poorly rmderstood. The Polyplacophora, known as chitons, have a flattened body covered with eight articulated plates of calcium carbonate. 

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