They have cool patchs of purple presumably from internal food stores of the animals food source, the sponge Dysidea . Then the larvae became these little crawling beanie caps. Sorry for my inexpertise with sea slug life stages, but further description for any of my appended photos would be appreciated. Sorry for taking so long to post these puppies. But the midnight when I discovered that they had hatched, I rounded up a poor graduate student to help me photograph them.
Sea slugs are a driving inspiration.
It was certainly worthwhile you taking up my idea of seeing if you could get the eggs to develop. Your photos show that Hypselodoris zebra has lecithotrophic larvae. In some cases the lecithotrophic veliger can spend only a few minutes or hours before settling, in other species they last for a few days before settling. I have never seen larvae with the brightly coloured pigmentation these ones do. You have caught the larvae at such an early stage in their development that there does not seem to be any sign of rhinophore buds, and the larval kidney is still present.