term "endolith", which defines an organism that colonizes the interior of any kind of rock, has been further classified into five subclasses:

;Chasmoendolith: Colonizes fissures and cracks in the rock connected to the surface (chasm = cleft);Cryptoendolith: Colonizes structural cavities within natural pore spaces within the rocks. These pores are usually indirectly connected to the rock surface; (crypto = hidden) ;Euendolith: Penetrates actively into the interior of rocks forming channels and grooves that conform with the shape of its