This is, I think, a Severn’s Pygmy Seahorse.
These Pygmy Seahorses are incredibly difficult to film as they are so tiny. This one is about 1cm tall and, as you can see, love to sit attached to a piece of algae or hydroid and sway back and forth with water movement. it is a real challenge to keep them in focus for any length of time.
These Pygmies were only offically recognised in 2008.
