Seamoth.
Only ever seen it one time, which was in the Similan Islands about 5 years ago. Looks like a cross between a fish, a bird and an insect. There was a pair sitting on a rock for quite a while (I mean several weeks at least) on the dive site around Islands 5&6, which I called the Hideaway. I was freelancing on The Junk when I saw them, and recall when I got back on the boat after the dive, the tour leader Mick got very animated as (even with his X,000 logged dives) he'd never seen a seamoth and I had to explain exactly where they were. He'd just finished a dive but dashed off in the dinghy to find the seamoths! He loves his critters, does Mick.