 The snail's shell is also unusual. The shell structure consists of three layers. The outer layer is about 30 μm thick, black, and is made of iron sulfides, containing greigite Fe3S4. This feature makes this gastropod the only extant animal known so far that employs this material in its skeleton. The middle layer (about 150 μm) is equivalent to the organic periostracum which is also found in other gastropods. The periostracum is thick and brown. The innermost layer is made of aragonite (about 250 μm thick), a form of calcium carbonate that is commonly found both in the shells of molluscs and in various corals. The color of the aragonite layer is milky white.
