ABSTRACT
The terrestrial interstitial habitat or MSS (Mesovoid Shallow Substratum or Milieu Souterrain Superficiel) is the compartment of the terrestrial subterranean biome located between the base of the mineral soil horizon and bedrock. It is composed of a network of small voids, which may be found in one of two types of lithic aggregate: the screes on valley sides (colluvium), or, in volcanic areas, scoriaceous layers; and cracks and interconnected mesovoids in the superficial zone of the rock, including within lava flows (see Figures). The MSS is isolated from the surface by a mantle of soil; it may or may not connect with larger natural and artificial voids; and its depth varies from some tens of centimetres to several metres.
