Chitons are considered to be very primitive molluscs. Chitons are a very distinctive group because their protective armour consists of eight separate, usually overlapping, plates or valves held in position by an encircling muscular girdle.
The girdle is often marked with unusual spikes and spines. Chitons are long (elongate), usually flattened, and symmetrical. The Spiculed Chiton Acanthoplera gaimardi (on the left), as its name suggests, has a girdle of blunt spicules.
Chitons are adapted to living on hard rock surfaces. They have a very muscular foot, and when disturbed, can clamp down so that they cannot be dislodged unless their shell is smashed. Chitons can live for one to twenty years, or more.
Chiton sexes are separate, the eggs and sperm being shed into the water where fertilization takes place. The Snake-skin Chiton Chiton pelliserpentis (to the right) is a very common chiton on south-eastern Australian shores.
Chitons are particularly abundant in Australia, and the shores of southern Australia have the most species in the world. It is believed that Chitons first evolved there. Chitons belong to the class Polyplacophora.
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