This varicose phyllidia is a small nudibranch, which I saw several times over the course of a week or so. Apart from being a lot smaller than the clumpy nudibranchs I saw a couple of months back, the varicose phyllidia has gills under the mantle skirt rather than in an exposed, wavy clump.
This one was two to three inches long. In the middle photo, the tiny white-spotted toby and small brown surgeonfish give a sense of scale.
Graham's Island 
Gorgeous colours – I like how in the second pic the fish seem to checking out the nudibranch.
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Nudibranchs tend to be colorful. I guess it’s there way of warning potential predators that they’re poisonous.
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