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It looks pretty similar to Aglaja regiscorona Bertsch, 1972 in IPN at page 43.
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.
This species was posted on 24 August 2011 at these websites as Aglaja sp. 01 Genus: Renier, 1807, Zamora-Silva & Malaquias (2017) moved
Aglaja regiscorona Bertsch, 1972 into the new genus Niparaya Zamora-Silva & Malaquias, 2017.
I moved on 24 February 2018 Aglaja sp. 01 Genus: Renier, 1807 also into the genus Niparaya Zamora-Silva & Malaquias, 2017.
Manuel António E. Malaquias agreed (pers. comment) with Hans' statement that all records of Niparaya regiscorona outside of the eastern Pacific are misidentified and one or more disstinct species.
The only online picture of Niparaya regiscorona is the original line drawing published in the description of the species, as shown on Mike Miller's Slug Site.
Gosliner, Terrence M., David W. Behrens & Ángel Valdés. 2008. Indo-Pacific Nudibranchs and Sea Slugs.
Sea Challengers Natural History Books. Gig Harbor, Washington. 426pp.
Andrea Zamora-Silva and Manuel António E. Malaquias Molecular phylogeny of the Aglajidae head-shield sea slugs (Heterobranchia: Cephalaspidea): new evolutionary lineages revealed and proposal of a new classification
Zoological Journal of the Linnean Society, 2017, XX, 1-51
available online at https://academic.oup.com/zoolinnean/advance-article-abstract/doi/10.1093/zoolinnean/zlx064/4584517
How to cite:
Köhler, E. (2018), published 24 February 2018, Niparaya sp. 01 Genus: Zamora-Silva & Malaquias, 2017
available from https://www.Philippine-Sea-Slugs.com/Cephalaspidea/Niparaya_sp_01.htm