Crepter

Two crepters on a rock, seen on a misty morning. Crepters are barnacle-like, sessile organisms that eat whatever edible debris settles on their slime, usually microbes borne on the wind.

Their reticulated outer layer is shed to form two crusty, calcified shells that give them a degree of protection. The darker inner layer is tougher and denser than the grayer outer one; the grayer outer one is made when the first armor layer is shed to make room for growth. The outer layer may crackle and crumple if trod upon, while the inner layer is as hard as a rock.

Bunny Crabs ([link]) eat crepters.