I call this undescribed species of Trinchesia the rasta nudi because it has a wild set of dreadlocks. It can be tiny and notoriously difficult to spot. If you manage to find one you'll never forget it! I've been spotting them in the 10-14 metre range.
Tularia bractea - let's face it this nudibranch is so small that it's really not commonly known. But if you had to give it a common name then you could go with Metallic tularia. Recorded from the Poor Knights Islands, Bay of Islands and Danger Rock in October 2016.
I first encountered this species at the Poor Knights Islands on 18 July 2011. I discovered it quite by accident. I was zooming in on a photo I'd taken of a crested blenny and noticed a couple of teensy nudibranch-looking blobs next to the fish - they were blurry. The next day I went hunting in earnest and discovered Landing Bay Pinnacle absolutely covered in these tiny molluscs. They were all over the place, but at about 2mm long, a bit difficult to capture in a photo with my Canon G9 camera.
Years on, these sea slugs have popped up on my radar again. I spotted them in Manta Bay and on Magic Wall at the Poor Knights Islands on 24-25 September 2016. This specimen is from Danger Rock outside of the Bay of Islands (9 October 2016). It was in a depth of about 14-16 metres.
Runcina katipoides is a sea slug but not a nudibranch. It is truly tiny; the slugs I've seen have been about 2-3mm long. It is probably more common than you might believe but its diminutive size makes it difficult to spot unless you're really trying to find micro molluscs.
This photo was taken with my Canon 5D Mark II using a 100mm macro lens. The photograph has been heavily cropped so that you can see the sea slug.
Photographic confessions of a nudiholic!