Can we agree on an ecological classification of subterranean animals?

That the ties between any obligate subterranean species and the hypogean environment depend on the interplay of a species' own physiological characteristics and all of the ecological characteristics of the adjacent epigean habitat(s), including biotic factors, has been emphasized. The reasons why troglomorphy cannot be included within criteria for classifying cave dwellers have been demonstrated. After a review of historic classifications, standardized definitions of the most widely used terms are proposed. The most easily recognized are four categories which are terminological approximations of the classic Schiner-Racovitza terminology: (1) troglobiont is a species or population, strictly bound to a hypogean habitat; (2) eutroglophile is an essentially epigean species, but able to maintain a permanent subterranean population; (3) subtroglophile is inclined perpetually or temporarily to inhabit a subterranean habitat but is bound to the surface for some biological functions (e.g. feeding); (4) trogloxene is a species only occurring sporadically underground.