Life of a baby sand dollar

Christy Varga adjusts a dial on the microscope.

On the wall above, twelve white circles on a screen lock into focus.

“These look good,” Christy explains, pointing at the screen with a green glove. “See how the surface of the yolk is all wrinkly? That’s a good sign.” Each little dot is a sand dollar egg.

Our aquarist Christy has been breeding sand dollars like these for over a year—it's the first time we’ve cultured sand dollars here at the Aquarium. Thanks to this behind-the-scenes work, visitors can now see cultured sand dollars on display.

A sand dollar (Dendraster excentricus) looks nothing like the smooth, white discs often found at the beach. (That’s actually a sand dollar’s skeleton!) A live sand dollar doesn’t look like money. A type of flattened sea urchin, it sports shades of purple and grey and moves around with hairlike spines.

Breeding these invertebrates requires time, careful work, and gentle care. First, the eggs need to get fertilized. But with virtually indistinguishable males and females, how do you pair them? Encouraging adult sand dollars to spawn (release their eggs and sperm) allows us to see who’s who—eggs come out red and sperm comes out white. After spawning, Christy collects sperm and fertilizes eggs.

A fertilized egg quickly begins to divide and grow. Over the course of several weeks, it sprouts arms: first two, then four, six, and finally eight arms. At this stage, this planktonic (floating) sand dollar baby is called a pluteus. It floats and drifts for about two weeks, then settles and makes its home in the sand.

In total, the time between when an egg is fertilized and when it starts to look like an adult sand dollar is about three months. Though at three months old, the young sand dollar is still small—barely bigger than a grain of sand!

Visitors can see Christy’s baby sand dollars—now about one year old—on display at the Aquarium. “I actually call them sand dimes because they're so small,” Christy says.

To see the sand dollars for yourself, head over to our Monterey Bay Habitats exhibit. You’ll come across a glass dome glowing like a moon in the dark hall. Inside, you can see over 300 juvenile sand dollars wave their tube feet and half-bury themselves in sand with hairy-looking spines.

Look closely and notice the sand dollar’s interesting anatomy. It has a beautiful “flower” pattern created by tiny openings. Tube feet poke through these holes, helping the animal breathe, access fresh seawater, and nab food out of the passing current. In turbulent waters, a sand dollar stands vertically to help direct goodies to its mouth.

By breeding and culturing animals instead of collecting them in the wild, we can reduce pressures on the environment. Christy’s work culturing them here at the Aquarium marks an exciting step that will help showcase these animals and protect their marine ecosystems.