Telling this nudibranch apart from the Red-fingered or Coryphella pseudoverrucosa is just about impossible. They appear to be almost identical.  They are found feeding in the same territory and their primary prey (hydroids)  appears to be the same as well.  Add to this the fact that both have undergone taxon changes in the past few years and it can be quite baffling.  I suggest that if you are confused, it is a good idea to throw an image out to the inaturalist community and see where you get.  In my humble opinion, and the opinion of a few experts the aeolids pictured below are Himatina trophina.  For now, I will go with that.  They tend to be a little less red than the Coryphella, have larger rostrums (noses) and shorter rhinophores and tails.  Good luck.  Some of the individuals photographed here are as small as 5 mm.  Others as large as 35 mm (just over an inch).  In the intertidal zone, they tend to be very small.