Oikozetetes is a scleritome-bearing Cambrian organism which may be related to the halkieriids. They bore two morphologically different shells, which were probably calcareous while the organism was alive (although diagenesis sometimes replaces the original minearal with another, such as silica). It is thought to also have borne an armour coat consisting of biomineralised sclerites, like Halkieria. These are never found in direct association with the shells, but there are many biostratinomic processes which could account for this fact.