A system is proposed for classifying the species occurring in the hypogean environment in relation to their ecological and evolutionary characteristics. The ecological criteria utilized relate to the preferred habitat of the animals (the epigean, endogean or hypogean environment) and the evolutionary criteria specify the grade of adaptive modification in three characteristics: reduction of eyes, amount of pigmentation and extent of elongation of the appendages. The object of developing this classification is to provide a system appropriate for those regions - such as those with volcanic rocks - in which the cave faunas include elements originating in different environments, and in which the species show very variable adaptive grades, depending primarily on the antiquity of the island or other distinct geological zone, where they are found.
Martín, Josè L.; Helga García; and Y. P. Oromí.
Classification of terrestrial subterranean fauna of volcanic substrates in the Canary Islands.
International Journal of Speleology,
Available at: https://digitalcommons.usf.edu/ijs/vol30/iss1/2