Classification 
Evolution and extinction 
Morphology 
Ecology 
Anatomy 
Reference and Links 
The Hooper Virtual Natural History Museum
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Trilobites
T he trilobites were one of the most successful groups of organisms to have ever lived. The first trilobite appeared in the Lower Cambrian and became extinct by the end of Permian. In their 350 million years of existence, trilobites evolved into diverse forms adapting to different marine environments. Trilobites are among the first to have developed the highly sophisticated visual organs.
Trilobites are arthropods, their bodies divided into segments; protected themselves by exoskeleton. Compound eyes in trilobites are thought to be related to the compound eyes of the modern arthropods. Modern day arthropods include spiders, shrimps, lobster and other joint-legged organisms.
The most characteristic feature
is the three lobes found along the posterior-anterior axis. Its
name is also derived from this characteristic: tri-lob-ite (three
lobed things). The largest trilobites were measured up to more
than a meter long and the smallest reached a few millimeters.
On average, trilobites are two and seven centimetres long. Some
had spikes all over the body. Some lacked eyes or had elaborate
extensions.
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