Rough-mantled Nudibranch (Onchidoris bilamellata)

Tidepool Tim says,  "This is the easiest nudibranch to find.  They are big, obvious, and abundant. that said, a few years ago there must have been some die-off as we couldn't find one anywhere!  Most invertebrates are like this - they have good years and off years in terms of spawning, settlement, and recruitment. These animals have two "horns" like antenna at the front and at the back you will see a ring of feathery structures which are their gills.  They resemble garden slugs when you pick them off the rocks. Their eggs are kind of neat - see in the pics - they look like layers of lasagna noodles attached to rocks - usually with a great herd of nudibrancsh settled alongside. Very impressive when you see them!  Go sea slugs!”