Deep-sea dorid nudibranch (Bathydoris aioca)
A large, deep-sea nudibranch, or sea slug, this gastropod is found on soft sediments in the deep NE Pacific. One was seen near the anchor of the Slope Base Shallow Profiler mooring, and was 30 cm (nearly a foot) long. They have a bumpy exterior, long, thin feeding tentacles, tiny ear-like rhinophores (which act as chemosensors), and posterior external gills.
Reference:
http://dsg.mbari.org/dsg/view/concept/Bathydoris%20aioca