An extinct marine arthropod common from the Cambrian to Permian eras (570-245 million years ago). Trilobite fossils are abundant in rocks of this period. Trilobites were 10-675 mm long, and their flattened oval bodies were divided into three lobes by two longitudinal furrows. They had a single head shield, which bore a pair of antennae and, in many species, insect-like compound eyes. This was followed by more than 20 short body segments, each with a pair of forked appendages. Many trilobites apparently burrowed in sand or mud, preying on other animals or scavenging.