Looks like a black porcelain crab. There seems to be a few species under the same common name as per usual, this looks like a “flat top black” porcelain crab.
Probably Petrolisthes armatus, the Green Porcelain Crab, though straight-on pics of the top of the crab under white light would help to confirm.
The orange markings can be tough to see in a lot of pics, but they're fairly visible in others; this is probably due to how the crab is holding its claws in the pics - for example, you can see in the pic below that one of the orange spots would be visible from a distance while the other likely wouldn't: