Adaptation
The blind cave eel isn't so much defined
by its morphological features, but rather by its lack of
morphological features. They lack even the most basic, at least
when considered in reference to other organisms it is related
to, features. The appearance of these troglobites are completely
opposed to our preconceived notions of how “animals” or “fish”
look. These misunderstandings of the way that taxonomic terms
are applied become more pronounced when the appearance of the
blind cave eel is examined in more detail.
The blind cave eel lacks eyes. This simple fact seems so appalling because we are so reliant on our eyes. For many years people considered troglobite organisms to be undergoing “regressive” evolution or to be evidence for Neo-Lamarkism. (Romero, 2001) Regressive evolution comes from our deep-seeded notion that we are the apex of what evolution has to offer. Every organism should be aspiring to ascend the evolutionary mountain to reach the peak that is the human form. Thus, any organism moving farther from how we are structured must be moving down the mountain towards a more primeval from, IE regressing. Neo-Lamarkism suggested that the atrophy of the optic tissue coming from the disuse of these tissues in the opaque subterranean environment was passed onto the offspring of these organisms. However, the observation of many troglobites and their convergence on the same form has debunked both of these theories. Without eyes these organisms have had to develop other means of sensing their environment.
The lateral line of Ophisternon candidum is well-defined and runs from the length of the organism. (Mees, 1962) This specialized group of cells allows the blind cave eel to sense vibrations and other movements in the water around it. The possibilities of the applications of a well-developed lateral line system compensates for the lack of vision. Moving towards a detection system that doesn't rely on light would obviously be advantageous for organisms that live in a very light deficient environment. This system could allow the blind cave eel to detect prey and other organisms around them. Light may be unavailable, but no matter the environment movement in water will always create vibrations that the lateral line system will be able to detect. The lack of light has affected the morphology of the blind cave eel in another way: their lack of pigmentation.
Pigments are used to absorb the sun's light to avoid the damage that can be caused by the UV-radiation. Without any sunlight to protect yourself from the use of energy in the creation of pigments is a distinct disadvantage. So, selection pushed the blind cave eel to lose its pigmentation. The skin of these organisms appears to be a whitish color. (Mees, 1962) While many may see this lack of pigmentation as strange, when viewed in the scope of evolution this characteristic makes perfect sense. Many adaptations of stygofauna deal with the lack of light, but not all.
The elongated form of the blind cave eel's body (Mees, 1962) also serves a distinct function. This body shape is similar to that of worms. Like worms, the blind cave eel makes use of this body form for burrowing. The blind cave eel is believed to burrow into the soft sediments in the walls of the caves, wells, and sinkholes that it lives in. (Bray & Thomas, 2011) The burrowing could serve as a method of searching for food.
When you put together all the adaptations of the blind cave eel and view them in the scope of evolution and its environment, and one can see that the blind cave eel is an extremely specialized and well-adapted organism. The lack of eyes saves the animal the energy of forming and maintaining such a costly organ that would be useless in an environment that lacks light. A lack of eyes led to a greater development of the lateral line system to be used in place of eyes. Likewise, pigmentation would serve no use in an environment without sunlight. The elongated form of the eel that allows for burrowing could help it to secure scarce food in a harsh environment. In these ways the blind cave eel has become specialized and has succeeded in an environment where many organisms would fail.