We found several of these on our 7 dives at Monterey. They're unbelievably lovely, especially when the cerata get to gently waving with the surge. At times they wave so much that they obscure the rhinophores and branchial plume, but that's okay, because the whole thing is beautiful. The scientific name is Okenia rosacea, popular name (according to Behrens) is Hopkins' Rose. They're not more than an inch long, and the ones we found were about as wide as they were long. Here's a single and a double:
