speculator. The trilobites are an extinct group of marine arthropods, with a hard segmented shell that is divided into 3 sections. P. speculator and similar trilobites lived throughout the Silurian and Devonian periods (around 435-345 million years ago). Most trilobites 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.