Trilobites are one of the oldest invertebrate species, appearing more than 500 million years ago during the Cambrian and disappearing during the mass extinction at the end of the Permian, approximately 250 million years ago. Perhaps the most famous fossils after the dinosaurs, more than 17,000 species of trilobite have been discovered all over the world. As marine arthropods, they are the extinct relatives of crustaceans, insects, arachnids, and centipedes. Trilobites are the earliest creatures known to have developed eyes for sight. Their name derives from the Greek for "three-lobed," and they would have used their plated armor to roll up into a ball to protect their more vulnerable undersides. This strategy served th🌺em well as they survived for almost 300 million years, making them one of the most successful species ever to live on Earth.