 Starting with an indistinguishable proto-cephalon and proto-pygidium (anaprotaspid) a number of changes occur ending with a transverse furrow separating the proto-cephalon and proto-pygidium (metaprotaspid) that can continue to add segments.Segments are added at the posterior part of the pygidium, but all segments remain fused together.The "meraspid" stages (anamorphic phase) are marked by the appearance of an articulation between the head and the fused trunk.