A juvenile perhaps? Only about 2" long
Wrigley institute of environmental science.
Found on shore, pushed back into water and it excreted purple ink.
Striped Sea Hare in Long Beach
Laying Top Ramen instant noodles all over the side of the harbor.
Found on pilings of Prisoner's Harbor Pier at ~3m depth. There were a fair number of Aplysia both on the piling and on the adjacent sandy substrate, including a few deceased ones (they bleach in color when they die). This was also one of several Aplysia egg masses encountered.