Trilobite
U.S. Geological Survey photo by E. H. McKee. (fair use policy)
Trilobites lived throughout the Paleozoic Era (550 to 250 million years ago) and inhabited every continent. A primitive member of the arthropod family, trilobites went extinct in the great Permian-Triassic mass extinction. Most of them lived on the sea floor, grazing in the mud or hunting smaller creatures there.
Trilobites are named for their three-lobed body form, consisting of a central or axial lobe and symmetrical pleural lobes on either side. In this trilobite, the front end is on the right, where its head or cephalon ("SEF-a-lon") is. The segmented middle part is called the thorax, and the rounded tailpiece is the pygidium ("pih-JID-ium"). They had many small legs underneath, like the modern sowbug or pillbug (which is an isopod). They were the first animal to evolve eyes, which look superficially like the compound eyes of modern insects.
By far the best place on the Web to learn more about trilobites is www.trilobites.info.
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