Anchored off a calm sandy beach, I rowed ashore and
found many beautiful white shells or ‘tests’ of once-living
sand dollars scattered about. Shells, sure, but I wondered
where these creatures lived. On a minus tide, I returned and
was surprised to find thousands of these off-center reddishbrown
creatures that are close relatives of sea urchins almost
entirely covering the beach. While urchins, are purple and
cylindrical in shape and have long spines, sand dollars
have flattened reddish bodies that are off-round shaped or,
as their scientific name (Dendraster excentricus) implies,
eccentric. Also called ‘sea-cake’ or ‘biscuit urchin’, these
creatures don’t lie flat on the sandy bottom except when
they’re moving about. Instead, they upend themselves and
stand erect to catch floating debris that they pass with feet
and spines to a central mouth.
They anchor themselves with those same tiny tube feet to stand angled so their undersides and mouth catch the current. When in a good flow of water, they gather in groups all lined up like little
soldiers as they funnel and filter water. In heavy currents,
young sand dollars will swallow sand to keep them in
place, but they actually move around rather a lot in search
of better feeding grounds. Able to live at least 13 years –
which can be proved by counting the test’s rings, large
colonies develop and 625 sand dollars per square yard have
been counted in some areas, making for many tight rows
of little upright disks all jammed together. Sand dollars
have few predators, but can quickly bury themselves
if a sea star or crab walks through a sand dollar colony.
A few sand dollar shells make for an interesting beach –
but imagine what it must be like just a few feet offshore.
Larry Eifert paints and writes about wild places. His work is in many
national parks across America – and at www.larryeifert.com.