This was one of a few tiny blue creatures clinging to the side of our boat as we came up from a dive in Hahei, New Zealand.
It wouldn't surprise me if this was a rather common creature and possibly well known, but I wouldn't have a clue where to begin looking for proper identification as I cannot even fathom a guess as to the correct taxonomic classification.
At most 3mm long, this was the best photo I could manage I'm afraid, but I'm hoping it contains enough detail to make out what it is. I've also attached the other photo I got, but that was at f/32 and rather fuzzy as a result.
Thanks for all the help everyone!