In "A. superstes" the central canals of sclerites are flattened on their upper surfaces, and this produces a depression on the upper surface of the tip. The surface of this depression is not mineralized, which suggests the depression may have helped the animals' sense of smell by letting chemicals in the water penetrate the exposed skin. The phosphatic coating on sclerites of "A. superstes" has features that suggest they were originally covered by a thin organic skin. An outer organic layer has also been found on sclerites of the chancelloriids, sessile organisms that are thought to have looked rather like cacti. If halkieriids were early molluscs, the outer layers of the sclerites may have been similar to the periostracum of some modern molluscs.