My back ached. And we were thoroughly enjoying ourselves.
It was a real treat to see this bright blob of yellow on a rock above the water level, and with a semi-dry spot above it to lean on.
I got a hand underneath and gently pushed at it. It came off the rock easily.
It does look like a lemon.
This was about 2 inches long, grainy on top, and semi-firm, not hard like a starfish, but with less give than a worm or a clam siphon. It lay on the rock where I put it, not moving, not trying to escape. I flipped it over:
Underside. Definitely snail-like.
I recognized it as a Dorid nudibranch, the sea lemon. A young one; they grow up to twice this size in the intertidal zone, twice that in deeper water.
The scattered black spots on the back and the white gills (next photo) distinguish it from the other local sea lemon, Archidoris montereyensis. "Archi" has black spots, but they extend up some of the tubercles, those bumps on the back (second and next photos). And "Archi's" gills are yellow or brown.
Sea lemons typically have a strong fruity odor when they are disturbed. I bent to smell this one, but all I smelled was salt water and seaweed. I guess I must have been gentle enough, even while I flipped it over.
When I returned it to the water beside the rock, it quickly turned and moved away into shelter. At least I got a photo of the gills before it was out of sight.
Sea lemon, heading for cover.
Here, you can see the round gill* plume on the rear. Up towards the front are two conical spikes, the rhinophores, which are the sensory organs. While the nudibranch (which means "naked gills") was on the rock, it kept these and the gills retracted.
*In the case of Dorid nudibranchs, like this one, they are not actually gills, but gill-shaped branchial plumes. Other sea slugs have different respiratory organs, such as the cerata of Melibe leonina, like the one we found on the White Rock beach.
It disappeared, and we straightened up and stretched our backs, and took another cautious step. There were acres and acres of seaweedy beach to examine still.