I know better, now. Thanks to Aydin.
Boundary Bay beach has been taken over by millions (billions, trillions?) of Batilaria attramentaria, the invasive Japanese mud snail. Laurie photographed them a couple of years ago; mottled, brownish, sharply conical snails up to about 4 cm. long.
Photo from my Flickr page.
Another Batilaria attramentaria. Photo from NOAA photo library.
A couple of days ago, on the north end of the beach, I noticed that the snails were different; some were smaller, and elegant in stark black and white stripes, others wore some combination of the usual pattern with black and white. I took a few photos, to look at later.
I don't know if these are the same species, or a different one; Googling Batillaria images, I found several black and white ones, including a B. attramentaria. But these are smaller, besides. The large one I brought home is barely 2 cm.
At home, when I blew the photos up to full size, I noticed something else; peeling.
The snail at lower left is missing the outer shell on the bottom loop. The brown and white little one, second from the right, seems to be also missing a segment.
A few more. Three are "peeled".
And here's one that's drilled; see the hole?
Aydin explains that crabs peel back the fragile shells of small snails to get at the animal inside. I asked how big the snails have to get before they are safe; he wasn't sure. Ridges and bumps on the shell serve as a protection, but these Batillaria are fairly smooth. And small; I have seen a few about 4 cm. long, but most are closer to half that.
The drilled hole may have been made by
It's a dog-eat-dog world out there.
Molted crab shell. Nice big pinchers for cracking snail shells.