Found this wonderful isopod, probably some kind of Idotea, and most of my pics seem to have it's head in shadow, lending it a Hadean demeanor that is completely unwarranted, but pretty cool all the same. Note that weird yellow thing under one of its plates (sclerites? what do you call them for crustaceans?): some kind of parasite?

Walking roughly through this key, my guess is that this is Idotea schmitti, mostly based on the blunt process on the pleotelson. Anyone have any thoughts? This was about 5 or 6 cm long, found in the rocky intertidal near Pescadero, CA, between San Francisco and Santa Cruz.