Anguila ciega  (Ophisternon infernale)

Like many cave-dwelling species, the Anguila ciega, otherwise known as the blind swamp eel, has lost its eyes and pigmentation, which are of no use in the dark depths of a cave (3). Instead, this fish has a large number of sensitive pores on its long, bulb-shaped head to detect environmental stimuli (2) (3). This is a very elongate fish with an exceptionally long tail, giving it a somewhat worm-like appearance (2).