 Trilobite development was unusual in the way in which articulations developed between segments, and changes in the development of articulation gave rise to the conventionally recognized developmental phases of the trilobite life cycle (divided into 3 stages), which are not readily compared with those of other arthropods.Actual growth and change in external form of the trilobite would have occurred when the trilobite was soft shelled, following moulting and before the next exoskeleton hardened.Trilobite larvae are known from the Cambrian to the Carboniferous and from all sub-orders.