Maria Elina Bichuette & B.G. Kapoor 
Biology of Subterranean Fishes [PDF ebook] 

In most habitats, adaptations are the single most obvious aspects of an organism”s phenotype. However, the most obvious feature of many subterranean animals are losses, not adaptations. Even Darwin saw subterranean animals as degenerates: examples of eyelessness and loss of structure in general. For him, the explanation was a straightforward Lamarc