Trilobite fossil. Fossilised Pillentina sp. trilobite. The trilobites are an extinct group of marine arthropods with a hard, segmented shell that is divided into 3 sections. They lived from the Lower Cambrian to the Upper Permian period (543-248 million years ago). Most were bottom dwellers, feeding either on organic sediment or by catching their own prey. Many trilobites could roll themselves up into a ball when threatened. Assuming this position ensured that only the shell was exposed, defending the animal from attack. Found in Morocco.