Click the thumbnail photos to enhance!
It looks pretty similar to Aglaja regiscorona Bertsch, 1972 in IPN at page 43 :
Gosliner, Terrence M., David W. Behrens & Ángel Valdés. 2008. Indo-Pacific Nudibranchs and Sea Slugs. Sea Challengers Natural History Books.
Gig Harbor, Washington. 426pp.
Aglaja regiscorona was originally described from Bahía Las Cruces, Baja California Sur, México, there are records of it from Costa Rica, and from the Galapagos Islands, according to IPN also from Midway Atoll, and from the main Hawai'ian Islands, from the Marshall Islands, and from Japan.
Either this species is very variable, or some of the specimens are misidentified.
I asked the author Dr Hans Bertsch on this, here is his answer: "I strongly suspect that all records outside of the eastern Pacific are misidentified, and may well be a new species. Similar in "general" form, but there are some significant body shape differences, more "compressed," more compact, fatter in the middle; form and length of the shield, etc." and: "In almost 40 years, I have not seen it again in the Sea of Cortez, nor have my students in the La Paz region, where it was originally found."
Thank you, Hans!
IPN Aglaja sp. 4 is also pretty similar, it differs by its more elongate shape, by the longer "'tails", and by orange spots on the head.