A very pretty porcelain crab — wouldn't you like to have blue spots like that? We think this is a Chocolate Porcelain Crab (Petrolisthes manimaculis; note that 'manimaculis' means 'spotted hand'). But I neglected to look for a confirming characteristic in the field — an orange spot inside the base of the movable finger of the claw. (If you have an opinion about the i.d., feel free to chime in.)
This individual was photographed on Bodega Head on 4 July 2012. The entire crab was ~4 cm across.
Chocolate Porcelain Crabs are reported to reach their northern range limit near Bodega Bay, but we've found them as far north as Fort Ross.
This species is potentially the least common of the four species of porcelain crabs on Bodega Head. We'll feature the others in future posts!