The Sandfish
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."
Cahuilla tribesman
Aucun commentaire:
Enregistrer un commentaire