Asaphida is a large, morphologically diverse order of trilobite found in strata dated from the Middle Cambrian to the Silurian. The order contains six superfamilies (Anomocaroidea, Asaphoidea, Cyclopygoidea, Dikelocephaloidea, Remopleuridoidea and Trinucleioidea), but no suborders. Asaphids comprise some 20% of described fossil trilobites.The Asaphida generally have cephalon (head) and pygidium (tail) parts similar in size, and most species have a prominent median ventral suture.