A trilobite is part of a group of animals known as arthropods. They are from the class Trilobita. Although trilobites are now extinct they first appeared 528 million years ago during the Cambrian Period. They eventually became extinct during the End-Permian mass extinction 251 million years ago. In total there were more than 17,000 different species of trilobite worldwide.
Trilobites were all adapted to their living conditions. Some were able to swim or walk across the sea floor, others behaved like plankton and floated in the currents and some were able to bury themselves into the soft sediment on the sea floor. The one thing most trilobite species were able to do was the roll up into a ball when they felt threatened; much like today’s woodlice if they feel scared.
The name trilobite comes from their body shape. They are split into three (tri) parts in two directions. This includes three lobes (left, right and axial/central) running from side to side and then the head (cephalon), body (thorax), tail (pygidium) split lengthways. So basically they are tri-lobed.
Some trilobites managed without eyes whereas others had large eyes with many small lenses. This allowed the trilobite to see almost 360° around it. Some trilobites had up to 15,000 lenses per eye making them very efficient in moving around and hunting.