ABSTRACT
Troglomorphy is not universal among cave organisms. In order for it to occur two factors have to be present: 1) a strong selection pressure for the development of a particular characteristic, and 2) the genetic and physiological or behavioural ability of the organism to respond to this pressure. Many cave organisms lack one or both of these factors. The phreatobite entomostracan crustacea and the extremely edaphic Collembola, such as the members of the family Onychiuridae, rarely show morphological troglomorphy. In many other groups, troglomorphy is questionable or inconsistent (Culver, 1982). It is also absent in cave environments such as guano piles or large masses of organic debris which are extremely energy rich. Peck has pointed out that troglomorphy should not be expected in these cases since troglomorphy only occurs when organisms are exploiting large volume spaces such as the surface of cave walls or floors (Peck, 1973), or large bodies of water. Indeed it has been long noted that the troglomorphic features of cave Entomobryidae are most closely approached in two very different surface habitats. The foot structure is closest to that seen in aquatic Collembola but the body shape features are most similar to those seen in forms (largely tropical) which live above the litter or soil, in trees. It is interesting that something similar to troglomorphy has been found in phreatobites where small size and elongate body form are developed convergently (Boutin & Coineau, 2000).
