Nudibranch Flavellina

I'd say neither. In this area there are three purple Flabellina spp.: F. affinis, F. pedata and F. ischitana. F. affinis can be ruled out as the cerata lack purple pigment on the outside of the cerata, especially near the tip. The other two are more easily distinguished by the shape of the rhinophores (rugose in F. pedata, strongly annulate in F. ischitana) but I'm afraid your photo doesn't offer much detail in that area. Yet, the ceratal clusters have conspicuous peduncles which are characteristic of F. ischitana, hence my suggestion.

Me recuerda a la película "La Sirenita".

It's been lovely seeing this recent spate of nudie photos.

Whatever it is it is beautiful!