The shellplates and the sclerites were probably made of calcium carbonate originally; it has been suggested on the basis of how they were preserved that they may have been wholly organic, but this is less likely since fossils of non-calcified organisms are usually thin films while "Halkeieria" fossils are three-dimensional like those of trilobites and hyoliths - in fact several specimens show curvature in the horizontal plane, which suggests that the muscles associated with the sclerites were still present at the