The coelosclerites ("hollow sclerites") of halkieriids and chancelloriids resemble each other at all levels: both have an internal "pulp cavity" and a thin external organic layer; the walls are made of the same material, aragonite; the arrangement of the aragonite fibers is in each is the same, running mainly from base to tip but with each being closer to the surface at the end nearest the tip. It is extremely improbable that totally unrelated organisms could have developed such similar sclerites independently, but the huge difference in the structures of their bodies makes it hard to see how they could be closely related. This dilemma may be resolved in various ways: