Here's a quick introduction to the Furry Crab (Hapalogaster cavicauda). [The best part is the video at the end!]
This species reaches its northern range limit at Cape Mendocino. We haven't encountered it very often in northern California, but we photographed two individuals on 12 February 2017.
In all of these photos, look for the short, dense setae (hair-like bristles) covering the carapace and claws that give this crab its common name. In the photo above, note the very broad abdomen curled under the body. Although you can't tell from these pictures, the abdomen on Furry Crabs is very soft. It's quite noticeable when you hold these crabs. Fun fact: Their scientific name — "Hapalogaster" — means "soft belly."
Here's a good view of the dense setae on the claws:
Here's a juvenile (and a slightly better view of the abdomen, curled under the body between the last pair of walking legs):
Eric put together a great video clip of Hapalogaster. Watch for a few different things — views of the dense setae; a close-up of the eyes; and some bryozoan "friends" living on one of its claws! [If you can't see the video below, click on the title of this post to go to the web page.]