Can you guess what this is?
It looks like a series of waves running towards the shore, doesn't it?
Here's another clue:
And this one will help a bit more:
It still might be hard to tell what type of animal this is.
You're seeing extreme close-ups (under the microscope) of a shell.
I'm guessing it will be difficult to identify the type of shell, so the next photo will reveal the entire shell as I found it on the beach:
There are a few things that stand out about this clam. It has a very oblong shape; it has narrow ridges that look like rays running towards the edge of the shell (more prominent near the margins); and it's very thin and fragile. (Yes, it's broken, but it's still worthy of sharing because it's a rare clam in this area!)
Meet Limaria hemphilli. I've seen various common names for it, but I think my favorite is Hemphill's File Clam. It was named after Henry Hemphill (from San Diego), who did a lot of the early work on molluscs in California...and its ridges give it a file-like appearance.
Limaria hemphilli is more common south of Monterey. In fact, most books list Monterey as its northern limit. But we've seen at least four individuals in Bodega Bay during the past ten years. I hope to photograph one alive some day — they're quite spectacular with many long tentacles reaching far beyond the shell. And they have interesting behaviors — they make "nests," and they swim like scallops!
P.S. If you're curious, there's a nice picture of a live Limaria available here.