I guess sand dollars aren't ubiquitous on beaches all over the world, or at least not in all parts of the UK and Australia.
After I mentioned them in a post below, Sian asked in the comment box, "What is a sand dollar?"
And I realized, "I have no idea."
Given that I grew up on the Oregon coast and have picked up countless sand dollars from local beaches over the years, and since I took marine biology courses both in high school and in college, my ignorance seems inexcusable. I know just a few, very basic, things that any casual beachcomber would know about sand dollars, and this, being pathetic, inspired me to look up the Western Sand Dollar or Dendraster Excentricus on the internet.
And now I know a few more things.
Looking at the top photo in the linked article, I've never seen a sand dollar that looked hairy and purple like that. The ones that we find along the beach tend to be white or grey, and most often they are broken into pieces. Occasionally, I've found greenish hairy ones (sort of like the purple ones in the picture), and I've seen a few non-hairy purplish ones, too, but most of the sand dollars I find are white.
Sand dollars wash up in the surf, or are uncovered, at low tide. Most of them are broken.The whole sand dollars I've found this past month range in size from 1/2-inch or less to a good 4" in diameter. The little ones are sweet and delicate.
"Hill" asked if I could post a picture of a sand dollar because she had seen one in America once but couldn't remember what it looked like. So, while I was at the beach a couple of days ago, I ran across an almost perfect sand dollar and many broken ones (which is far more common) lying in the sand, and I took some pictures.
This one is almost perfect. There's just that chip on the edge and a few small holes on top, but I brought it home and counted it good enough to be displayed with my whole sand dollars.
And here's a broken one. It's not uncommon to find them like this, but usually they are broken into smaller pieces.