Fauna of the mesovoid shallow substratum (MSS) in the Iberian Peninsula

When discussing subterranean ecosystems, most people typically think of caves and animals with striking morphological adaptations. However, there are other underground habitats apart from caves. The mesovid shallow substratum (MSS) represents one of these habitats, characterized by typical environmental features of underground environments such as, for instance, aphotic conditions or high humidity. However, it is situated very close to the surface and is formed by small fissures rather than large spaces, which contributes to its uniqueness. In this contribution, we review the most intensive and systematic studies of the MSS conducted to date in the Iberian Peninsula, focusing on the main discoveries regarding the fauna of this singular habitat.