Haminoea ovoidea can sometimes be found in large numbers in the Marshalls on shallow lagoon reefs in Lyngbya encrusted Halimeda patches and on sandy slopes at depths of 6-30m. This is certainly the species figured on Sea Slugs of Hawaii and in Gosliner et al (2008) as Haminoea sp. #2. As shown in the photos shown on the Hawaii site, many will attach their bubble-like egg masses to the Halimeda plants all at once.
Usually quite common, on 24 April 2011 they seemed even more abundant in some lagoon algae patches, many producing egg bubbles like the one below.
I like all the little tiny forams mixed into the algae and sand around the two specimens below.
Created 4 November 2007
Updated 3 February 2012