Blue-legged Sea Spider

Size about 30mm. I found this species while scuba diving in shallow water, but fully submerged. It was not in a hurry to get to the surface but seemed quite comfortable under water. It was quite quick to hide in some crevice though. In years of diving I have only met this species once, but I am sure it is common since its food is plentyful where I dive, but maybe the fluctuation in food availability does not maintain a constant population. This species is a known predator of opisthobranchia. See http://www.seaslugforum.net/find/pycnogon