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By the time the
sand dollar washes up on the beach, it's missing it's velvety covering
of minute spines, and appears somewhat bleached from the sun. The fragile
disk is the skeleton or 'test' of a marine animal. It's hard to believe
it was once alive.
Sand dollars are
from the class of marine animals known as Echinoids, spiny skinned creatures.
Their relatives include the sea lily, sea cucumber, star fish, and sea
urchin. When alive, the local species, Echinarachnius parma, is a
purplish maroon color of moveable spines, that encompass the entire shell.
Like its close relative, the sea urchin, the sand dollar has five sets
of pores, arranged in a petal pattern. The pores are used to move sea water
into it's internal water vascular system, which allows for movement. Also
sand dollars have suckers which are fueled by water pressure. The suckers
help the sand dollar slide into the sand to get away from predators
Sand dollars live
in low water, on top of or just beneath the surface, of sandy or muddy
areas. The spines on the somewhat flattened underside of the animal, allow
it to burrow or to slowly creep through the sand. Fine, hair like cilia,
cover the tiny spines. These cilia, in combination with a mucous coating,
move food to the mouth opening, which is in the center of the star shaped
grooves, on the underside of the animal.
The surface of
the sand dollar appears to have petal patterns, which are really tube feet
used for respiration. These tube feet combines with mucous coated cilia,
and it catches food that is favored by the sand dollar. Some of these foods
are cod, haddock, plankter, and organic particles. The sand dollar likes
to mainly feed on small worms and algae. The sand dollars eat the food,
by consuming it on the underside of itself, and with a set of five teeth,
chew and swallow its food. These mouths are much like a bird beak because
it can be used to scrape things like algae off of rocks.
The sand dollar
has many predators. Sand dollars have no way to protect themselves, except
for camouflaging themselves in the few inches of sand they are under. Their
main predators are starfish, birds, otters, flounder, crustaceans, and
octopus. Sometimes, crabs cause damage, because they nip at the sand dollar,
and with their claws. Sometimes, it will eat or attack the sand dollar,
and then leave it alone, to die.
Sand dollars also
die from heavy storms. When severe storms hit, sand is shifted all around,
which can bury a sand dollar in 12 inches of sand. This disables the sand
dollar, and it cannot escape. Another mass mortality is, from high temperatures.
Sand dollars can survive in water that is 95°F for only three hours.
One type of sand
dollar, is called the keyhole urchin, or the keyhole sand dollar.
On the keyhole sand dollar, there are 5 shaped slots, that look just like
a keyhole. This feature gives the keyhole sand dollar, its name. The skeleton
is rarely found on some beaches. Once the tan urchin dies, the spine will
fall off, and the skeleton is bleached white. Many times, dead sand dollars
are found, but they are chipped. These urchins, just like other sand dollars,
live on the tide line, where they can burrow deep into the sediment.
On the ocean bottom,
sand dollars are frequently found together. This is due in part to their
preference of soft bottom areas, as well as convenience for reproduction.
The sexes are separate, and gametes are released into the water column,
as in most echinoids. The free swimming larvae, metamorphose through several
stages, before the 'test' begins to form, and they become bottom dwellers.
The eggs are fertilized by the moving currents. They develop into tiny
swimming larvae. After a month, the larvae sink to the bottom, and then
start to grow a protective shell.
One type of sand
dollar is called the keyhole urchin, or the keyhole sand dollar. It is
related to a normal, plain sand dollar. On the keyhole sand dollar, there
are 5 shaped slots that look just like a keyhole. This feature gives the
keyhole sand dollar its name. The skeleton is rarely found on some beaches.
Once the tan urchin dies, the spine will fall off, and the skeleton is
bleached white. Many times dead sand dollars are found but they are chipped.
These urchins, just like other sand dollars, live on the tide line where
they can burrow deep into the sediment.
You can find dead
sand dollars on the beach after they have been washed ashore. People, for
hundreds of years, wear the fossil of sand dollars as jewelry, or use them
in various arts and crafts.
What Is A Sand
Since the sand
dollar lives in sandy locations, anyone who would like to collect their
shells, should comb beaches as the tide recedes. The very best time for
collecting, is after a heavy storm, as many of the shells that have died,
are dredged up by the increased wave action.
Click Big On Sand Dollar
© (1998, 1999, 2000, 2001) by Larry's Dream,