It’s a beachcomber’s prize.
But this sand dollar is just an empty husk… a skeleton.
This is what sand dollars really look like.
Off the coast of California, Pacific sand dollars snuggle up together, like a big pile
of purple sea cookies.
They’re fuzzy… almost cuddly.
But look closer…
That fuzz is actually made up of tiny spines… thousands of them.
Some long and spiky, other rounder.
Mixed in are miniature tube feet with grabby little suckers on the ends.
They use them to meticulously sift the sand and pass the grains down the line, until they
reach the sand dollar’s mouth - at the very center of its underside, buried under all
those spines.
Sand dollars eat sand.
They’re after the algae and bacteria that coat the grains.
And these sand dollars can also stand themselves up on their sides to use the long spines around
their edges to trap tiny plankton floating by.
So what about that part that looks like a flower with five petals?
It’s called the petaloid.
They have special tube feet there that help the sand dollar breathe, absorbing oxygen
out of the water.
You can see that same five-point body plan on the skeletons of their relatives - like
starfish and sea urchins.
In fact, sand dollars are just a type of flat sea urchin.
But while their cousins prefer the rocky shore, chock full of life and spots to hide….
Sand dollars don’t have such a cozy place to live.
They’re at the mercy of what’s basically an undersea desert,
Thrashed and sandblasted.
So being flat is an advantage.
They’re sleeker, streamlined against the powerful currents.
And they have another scrupulous solution for staying put.
Not all sand is the same.
Mixed in there are some extra-heavy grains.
They’re made of magnetite, a type of iron ore.
Scientists think that as they grow, young sand dollars sort them out and swallow them...
grain after grain.
The heavy ore builds up inside their bodies and helps weigh them down to the seafloor.
At the California Academy of Sciences in San Francisco, researchers used x-rays of sand
dollars to look for it.
See those bright white areas?
Those are the pockets of magnetite.
That’s how these tireless little creatures can hack it - out here in such turbulent waters
- where most other things can’t.
Turns out, it takes a lot of work to just lay around.
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