In the deep-sea trenches which Huntail call home, the Sun's light can not penetrate, so the vast majority of pokemon there – few discovered yet by man – never developed much in the way of eyesight. It seems an understatement to describe Huntail as the exception, for while their other senses are poorly developed, their eyes are as sharp as a Noctowl's.
The reason Huntail are able to use their eyes is because Huntail are themselves a light source. Their glow was once thought to be a means to attract prey, but pokemon with a sense of sight have learned the hard way over generations to swim away from and not into the light. Yet because most deep-sea pokemon are blind, Huntail can be living flashlights without scaring away their prey. The Huntail actually hunt much like Luxray, but are camouflaged not by invisibility, but by the swaying, silent motion in which they swim; they are as difficult to hear as they are easy to see. What little noise deep-sea pokemon hear is that of a Huntail's fishlike tail, so rather than a predator swimming towards them, there are always a few fools who swim out to greet a neighbor.
The depths of the ocean are a harsh environment, and none have made it harsher than the Huntail. Perhaps this is why so many pokemon who do thrive in such environments, such as Shellder and even Clamperl themselves, wall themselves off from the world until they gain the power which comes with evolution. And even without a shell, shyness has become a way of life; Relicanth were all too happy to be mistaken for extinct, and there are undoubtedly many other pokemon still just as glad to remain undiscovered by man.