7 swinging sand dollar facts

by Carolyn Kraft on 05/01/2012

Sand dollar

The sand dollar or Dendraster excentricus is one animal that continues to surprise me every time I see it. Long before I started learning about the ocean and marine life, I remember seeing faded-white sand dollar shells (former sand dollar endoskeletons) and not thinking much of them. Now I find sand dollars fascinating because they are just so strange. Drum roll please…here are seven swinging sand dollar facts:

1. Sand dollars live in…you guessed it! The sand. Typically, the species Dendraster excentricus is found close to shore in the low intertidal zone to as deep as 30 feet from Alaska to Baja California. (The low intertidal zone is the area close to shore that is usually covered with water except at very low tides.)

2. For sand dollars, living right  next to each other in very large groups or beds is the way to go. Sometimes there are neighborhoods of sand dollars that are several square feet (suburban dwelling) and others stretch for miles across the sandy ocean floor (urban dwelling). (Here’s a good photo of sand dollars hanging out together.)

3.There are many species of sand dollars living around the world with a variety of common names including sea cookie and sand cake. Sand dollars also come in a variety of colors such as green, blue or black; the local California species, Dendraster excentricus, is purple.

4. Sand dollars are members of the phylum Echinodermata, which means they are echinoderms and closely related to sea stars, sea urchins and sea cucumbers.

5. It’s hard to believe, but this flat and round-shaped creature is designed for burrowing in the sand. Their bodies are covered with tiny spines (similar to a sea urchin’s spines but super small) that they use to dig. Once they’ve burrowed into a good position (see above photo) sand dollars keep their butt end above the sand’s surface to capture food.

6. The feeding strategy of sand dollars is fascinating. Their bodies are covered with tiny appendages to capture food particles small and large. Tiny cilia (extra small hairs) on the sand dollar’s spines sweep up small bits of food and tiny tube feet adeptly collect larger food pieces. Once food is caught the tiny appendages on the sand dollar work together to sweep food towards the mouth, which is located at the center of the five-petal flower pattern on bottom. The mouth has a five-toothed set-up called Aristotle’s lantern for chomping food. (Five pattern symmetry is a characteristic of echinoderms, sea stars have five arms, etc.)

7. Sand dollars reproduce by spawning; male sand dollars release sperm and female sand dollars release eggs into the water during spring. Reproduction is assisted by sand dollars living so close together. In fact, this post is very timely since it’s May 1st, coinciding with the beginning of sand dollar spawning season that continues through July. Sand dollars begin their lives as larvae and go through several larval stages before developing skeletons and settling on the ocean floor as the first step to adulthood. An adult sand dollar is about three inches in diameter and lives approximately eight years.

(Note: The above sand dollar facts are for the species Dendraster excentricus, other sand dollar species may have slightly different adaptations depending on where they live in the world.)

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{ 10 comments… read them below or add one }

JNapoli May 2, 2012 at 10:21 am

These sand dollars are indeed swinging! I love how they live in gated communities, and any day with a reference to cilia is a good day! Thanks, OWT.

RMillan August 16, 2012 at 1:38 pm

I stay in a small village on the west coast of Scotland and spend many days with my daughter at the beach looking for marine life in small rock pools but most of the beach is sand and a few weeks ago i found one of these sand dollars which was shaped as round and it was floating in shallow water at the edge. im pretty sure it was a sand dollar but when ive googled it all it says is that they are from Calirfonia. Do you get these creatures in the sea’s of Scotland, UK and why was it floating?

Carolyn Kraft August 19, 2012 at 11:44 am

Hello RMillan,
There are many different species of sand dollars found throughout the world and I’m guessing you found a species local to Scotland’s coast. There may be more information available on the California species because it has been studied more, but it’s definitely not the only species out there. I recommend contacting the National Aquarium in Devon and ask them what species of sand dollars live along the UK coast.

A floating sand dollar usually means a sand dollar close to the end of its life cycle. It’s possible that a strong wave or predator knocked the sand dollar loose and it floated off or it died and was washed ashore, most likely it was the later scenario. I hope this answer helps!

ewna prnvqjner October 2, 2012 at 12:46 pm

OMG THIS SO HELPED ME WITH MY PROJECT THANKS SO MUCH

Jacob Jontson March 19, 2013 at 2:15 pm

THX U HELPED ME A LOT WITH MY PROJECT

Sand Feline March 19, 2013 at 2:16 pm

thx!
:)

Maureen Baker October 27, 2013 at 7:59 pm

My family visited Pacific Beach, Wa. recently. We have often found sand dollars on our Pacific Coast. This trip we saw what appeared to be the impression of the underside of the Sand dollar on the surface of the sand. Can you tell us what this is??????Thanks

hailey February 17, 2014 at 5:17 pm

thanks so much needed that very much

Elizabeth April 21, 2014 at 9:26 am

My ever curious nephew got a couple of sand dollars from the Easter Bunny & asked me if it was a shell or what. So thank you for these facts so I can sound smart!!

Carolyn Kraft April 22, 2014 at 4:00 pm

Glad I could help Elizabeth!

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