I took a walk on South Indian Island Park with a local hiking group. The first of their season, It was an ideal social outing, paced for getting to know each other. With a low but incoming tide, we walked as far out the beach as possible. Out and back total must’ve been around 3+ miles. A lazy lunch in the sand kept it casual.
Photo of the ships’ channel is dark but it gives you an idea of the location. It’s a beautiful beach with the Olympics over one’s shoulder.
I came across something I’ve never seen before. Masses of gold and black Sand Dollars were strewn about the beach. I’ve since learned they are called ECCENTRIC SAND DOLLARS (better than being plain or ordinary, I suppose.) A collection like this is called an AGGREGATION. Eccentric derives from that lovely floral pattern on the TEST (its skeleton) being slightly off-center. Sand Dollars are in the class called Echinoidea as are Sea Urchins. From AK to Baja, they make a home below the mean low tide line in mud or sand.
Sand Dollars skeletons or TESTS are made of Calcium Carbonate. Fine, tube like feet with cilia cover the flat underside. While alive, the skin that covers the test is covered in velvety spines coated in cilia (hair-like structures) that can be gray, brown, black or shades of purple. The cilia and spines give it mobility along the seabed. When they die, the tests become white or pale gray, bleached by the sun. The pretty, five petaled pattern in the critter are pores for gas exchange. The underside of the creature is the somewhat flat side. The center hole in this side is its mouth. Sand Dollars eat crustacean larvae, diatoms, algae and detritus.
Check out this video. Brace yourself, if you’re as nerdy as I you’ll gasp at what she shows you at the end:
This video shows a Sand Dollar actually using its cilia to move part of a shrimp to its mouth. Yah. It’s neat.
1) When threatened (sensing fish mucus) Sand Dollar larvae can clone themselves. This doubles their numbers and chances of survival.
2) Hydrofoil Design: This species will align in rows, dig their front edges into the sand and raise their back edges into the water. This makes the water pass over in a left to right fashion. The domed shape of the test draws food into their mouths. Now that’s cooperation.
3) The eggs are covered in a thick goo to keep the adults from eating them.
4) Seastars, some Flounders, crabs and sea gulls will eat them. Big storms or a really low tide at a very hot time of day can cause massive desiccation. 2-3 hours of air exposure will kill them as well. I once came a cross a beach on Vancouver island covered in ghost-white tests and wondered why. Perhaps that was why.
5) They can live up to 13 years. The pores in the PETALIDIUM (the floral shaped part) act like tree rings in aging them.
How cool to come across these critters in a live state.
Next post we’ll look at BARNACLES. Oh man…fascinating.