The arthropods are a major group of animals that developed in the Cambrian period. They have jointed bodies and jointed legs. One type, called the trilobites, dominated the seas in Cambrian, Ordovician, and Silurian times and even hung on until the Permian before becoming extinct.
They looked a little like modern wood lice, or sow bugs, but lived in the sea. The many different kinds had a wide range of life-styles, but they all had a shell that was divided into a head shield, a jointed back, and a tail shield. They had many pairs of legs and gills underneath.
(A) BOTTOM DWELLERS
Heavy trilobites with eyes on stalks, like Encrinurus, crawled along the bottom of the sea.
(B) SWIMMERS
Swimming trilobites, like Deiphon, were light and feathery-looking.
(C) GROWING UP
As a trilobite grew, it would shed its outer shell. The new shell beneath was soft and could grow for a while before hardening.
(D) PROTECTION
Some trilobites, like Calymene, could roll up into a ball for safety.
(E) DIGGERS
Spade-shaped trilobites, like Trimerus, burrowed in the sand.
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