So this is called a flamingo snail, and they can often be seen on sea fans, but they are often not super vibrant in colour, and so are the sea fans. They can be pretty hard to spot.
But when you do night dives and you keep your eyes sharp, you can spot them sitting pretty like this from time to time.
It’s fairly challenging to get sharp images and good lighting at night underwater. But this one came out very nice!
I shout this on a canon eos R with a 50mm f1.8, obviously in an underwater housing. And I didn’t have underwater lights for my housing at the time, so I was using waterproof flash lights to light it