Nudibranch? in search of i.d.

Nudibranch, or similar, laying eggs by the wreck of the HMCS Yukon in San Diego. Photo by Robin McMunn.  What may it be?

Doesn't look like a nudibranch, nudis have gills on top.  Possibly a pleurobranch a side-gilled slug - those might be its gills under the mantle on LHS.

Diver Kevin (Kevin Lee ) photographed the same, what is it?  

Kraken,

Look here: https://www.shellmuseum.org/shell-guide

and then see the entry for "Pleurobranchaea inconspicua" under the "Family Pleurobranchidae"

Tom

Good call!  I would also consider Pleurobranchaea brockii, as it too matches the pattern of little and medium sized spots. 
Thank you for contributing to our appreciation of our underwater friends.
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Coleman, N., Cobb G.& Mullins D.: Nudibranchs Encyclopedia, 2d ed, 2015, p 79