|-Segmented animals with exoskeleton composed of chitin or calcium carbonate, with jointed limbs.
-Grow to length of 6-750mm by shedding exoskeleton and rapidly growing while new shell hardens.
-Body is divided into three main sections. The cephalon (head), thorax and pyguidium (tail), with classification of the order dependant on a disparite morphology of these parts.
-Limbs are only preserved in instances of exceptional preservation.
|-Order became fully extinct at the Permo-Triassic boundary.
-Two genera of trilobite still around at the P-T boundary which became extinct.
-No suvivors to the Triassic mixed faunas.