The Coryphella pseudoverrucosa is just about impossible to distinguish from the Himatina trophina.  There have been several taxon changes in the Flabellinidae family (of which this previously belonged) and my guess seems to be almost as good as that of the experts.  Apparently, the Coryphella pseudoverrucosa has a longer tail and rhinophores, a shorter nose (rostrum) and tends to have deeper red in the gills.  The individual pictured below seems to fit that description well.  The split rhinophore is unusual, but I have seen it before in other aeolids.  Should you have a scientific mind (or wish to immerse yourself in that kind of dialogue) this article regarding the taxon changes of the Flabellinidae family might be just the thing to keep you awake.