Trilobite (Naraoia compacta). Dorsal reconstruction of the trilobite, Naraoia compacta, from the Middle Cambrian Burgess Shale of British Columbia. This blind, soft-shelled trilobite had only two parts to its exoskeleton. Like other trilobites, however, its carapace was three-lobed, it had jointed walking legs with attached gills for oxygen exchange, and it had paired antennae. The head region shows two branched digestive glands connected to a central gut. It ranges in size from 9 to 40 mm.