Sand Dollar from Maine
I never got around to posting many pictures from our trip to Maine in July of 2019, so now is as good a time as any. We were at Bar Harbor. While many people were there for Acadia National Park, they mostly seemed interested in the inland hills and forests. What we were there for, though, were the beaches. And on the sandy beaches, one of the more common things was these Sand_dollars. I believe these were at Seal Harbor, which is a nice sandy beach that is relatively protected. The sand dollars tended to nestle down in the sand and lightly bury themselves, but running water as the tide went out washed away enough of their cover that we could see them.
Their dorsal side was darker with short fir, while their underside was lighter colored with a combination of what I think are movable hairs and tube feet.
Sand dollars are echinoderms, like starfish and sea urchins. They have a skeleton of sorts, that most of their body is inside of but their feet and hairs/spines project through. When they die and decompose, the skeleton is left behind, allowing us to see the patterns. Here is a dead one from the dorsal (upper) side:
and a closeup of the perforations through the skeleton.
Those pores are apparently the anus, excreting wastes into the seawater. The mouth is on the other side:
They don’t appear to have jaws or anything, they just pull in whatever small food items will fit in their mouths, and digest them. There are a bunch of short spines around the mouth when they are alive, but nothing that looks like a chewing mechanism.
Yeah, OK, they aren’t very exciting. But they are definitely something we don’t see back home in Lake Superior. In fact, there do not appear to be any freshwater echinoderms, so not only are there not and sand dollars in Lake Superior now, it is exceedingly unlikely that there will ever be any in the future.
Comments are closed.
Nice post. I live just a couple hours from Acadia National Park but have never seen live sand dollars on the beach. With the severe storms (4 now) we’ve had this winter many of our beaches have been completely rearranged. Even some lighthouses have been damaged.
Hopefully the Sand dollars, like starfish and sea urchins, are built to survive these disturbances.
The only place I’ve seen a live sand dollar is on the west side of Eleuthera Island, Bahamas. There they can be seen moving along in shallow water just under the sand. If you pick one up briefly it will quickly rebury itself.
I like to describe sand dollars is as flattened sea urchins. The fur you described are spines…they move around on these spines like urchins do. And the chewing parts are five plates, hidden inside the shell. The diversity of sand dollars is also quite interesting. I can instantly tell from your photos that they’re a different species from the ones we have on the west coast, as yours are almost perfect circular discs, while the ones we have here are off-centre.
Steve: This was the only beach that we found sand dollars on, it was a lot more protected and sandy than the other beaches. This particular beach was absolutely crawling with sand dollars, though.
Tim: Thanks for the notes. At this point, we’ve been to a number of ocean beaches, and even beaches fairly close to each other have wildly different communities. What really matters appears to be how much the waves crash on the beaches. The wave-beaten beaches in Bar Harbor and in Tasmania (on opposite sides of the planet) actually resembled each other more closely than the exposed Bar Harbor beaches resembled the nearby, more-protected beach where these sand dollars were.