Found two of them, each about 1/2", slightly different coloring. Off a dock, living in filamentous green seaweed. Very shrimplike tails. One of these photos shows them with a Syllidae in my photo box; the clung to it and rode it around but didn't try to eat it. ID as per: http://researcharchive.calacademy.org/research/izg/SFBay2K/Anthurid%20Isopod.htm