The sandfish, Cephalaspis desertii, is found exclusively in the California desert. It is the only species of Cephalaspidomorphii known that has survived the genus’ extinction during the Devonian period (420 mil. years B.C to 360 mil. years B.C.). It is believed to have appeared two hundred million years ago, living in what was then an area covered in a shallow sea. How it managed to survive during that 160-million year gap is unknown.
As the land began to rise and form the Rocky Mountains, the shallows were drained of their water. But the process was slow enough to allow evolution to keep pace.
Unlike most "modern" fish, the Cephalaspidomorphii have a bony exoskeleton covering most of their body. In the sandfish, this feature is even more pronounced. The whole animal is covered in seamless bone, head to flippers. This allows them to avoid loss of moisture, but requires them to shed their exoskeleton in order to grow. The exoskeleton is costly to produce in energy and nutrients, and tough to break. In addition, the sandfish is at his most vulnerable after having shed his old skeleton, and before having completed the new one. Because of this, sandfish only seldom shed their skin, and grow very slowly.
They have also evolved two separate mechanisms for breathing on dry land. First, their air bladder has been modified to have a greater surface, and thus absorb more oxygen. In addition, the gills are constantly immerged in mucus, to maximize gas exchanges. But the exoskeleton that prevents water loss is also hindering this exchange.
The sandfish has only one opening in his body, which is used to both absorb prey and excrete waste, as well as respiration. This double-function is used efficiently by the animal, since the smell of the waste and the high CO2 concentration is used to attract its prey, compensating for its limited mobility. Even though the same opening is used for both feeding and excretion, the sandfish does possess a full gastro-intestinal track, that doubles back on itself, so the entry and exit are situated next to each other. Again, the use of only one opening in the exoskeleton favors moisture-retention.
The sandfish uses highly modified flippers to crawl forward, but because of his heavy exoskeleton, his speed is very slow. To capture his prey, he uses what, at first glance, appear to be chelicerae. This confusion has caused the sandfish to be classified as an insect in the past, but a more detailed anatomical examination has shown that the pseudo-chelicerae are in fact modified fins, which the fish uses to drag insects into his mouth/anus, as well as to hermetically seal the opening to prevent moisture-loss.
Despite its many adaptive features, the sandfish has only a very short period of activity. Only at dusk and at dawn will this furtive creature spring into action, hunting the small insects that are its prey. During the day, the heat combined with the lack of oxygen forces it to rest in the shade. And during the night, the cold makes it sluggish, and it needs to maximize oxygen absorption in preparation for the day.
Nevertheless, its hard skeleton and adaptive camouflage mean it has very few natural enemies. Combined with its slow metabolism, which requires it to eat only one cricket every other day, the sandfish wages a war of attrition.
Due to the fact that Native Americans have a purely oral culture, no written records of the sandfish exist prior to European colonization. However, it is commonly accepted that the "Chief-stone" (so-named by early explorers because it was present in the chief's hut)of the Cahuilla-tribe is, in fact, a sandfish. The animal is believed to be revered by the Cahuilla-tribe as a symbol of fortitude and endurance, as well as patience. An ancient proverb of the tribe is seen by many as a clear reference to the animal:
"If you wait long enough, even in the desert will you catch a fish."