I found these crabs at the end of September, 2018. My family was vacationing on the coast of Lopez Island in the Pacific Ocean off of Washington State. I have been trying to figure out what they are ever since. I found two crabs, one that was orange and black, and another that was off-white and black. They are both about an inch and a half across and an inch from front to back. I did some research and the closest thing I could find are oyster crabs, which are found inside oysters on the East Coast of North America. (I found my information on oyster crabs here). However, I found these inside clams on the West Coast. Also, the pictures of oyster crabs I can find online (figure 1) do not look like my oyster crabs. I was wondering if anyone can identify these crabs. Sorry about the picture quality and thanks in advance!
What you have found are pea crabs, which have a fascinating life history of parasitism. https://www.whitestoneoysters.com/blogs/an-oyster-life/what-the-shuck-is-a-pea-crab