This is a noticeably spiny crab claw. Next question — which species of crab is it from?
The photo below is another hint. (And note the sandy habitat where this crab lives.)
The picture above shows a distinctive crab carapace, with dramatic spines.
This species might be more familiar to those of you living south of San Francisco. It's a Spiny Mole Crab (Blepharipoda occidentalis). I've written about them once before; you can review previous photos from Doran Beach and Salmon Creek Beach here.
Most people are probably more familiar with the more common Mole Crab (Emerita analoga). In contrast to Emerita, Spiny Mole Crabs can grow to be much larger; they have dramatic spines; and as the mystery photo shows, they have claws. They use the claws to scavenge and tear apart food. The spines on the outer edges of the claws and the carapace probably help to deter predators (such as fish).
I don't have a digital photo of a Spiny Mole Crab, but you can find a nice picture of the entire crab here (by Zen Faulkes) and on this EOL page.
I'm writing about Spiny Mole Crabs again because we're interested in whether anyone has found them north of Salmon Creek Beach.
Recently, we counted many more molts than usual, so it's possible Spiny Mole Crab numbers have increased in our area, which also means there is potential for them to be found even further north than previously documented.
Below are two more examples of Spiny Mole Crab carapaces (two different sizes). Let us know if you see a Spiny Mole Crab carapace or claw on a beach near you!