This feathery looking thing is actually a worm. It’s a Southern fan worm Sabellastarte australiensis
Sometimes they are even called Feather Duster Worms and just like its cleaner namesake those appendages sweep the water clean hoping to find nutrition in the suspended particles floating by.
Photo: Robert Rath, ‘Feather Duster’ 1/200s f/32 ISO100 100mm
Ain’t too many particles floating around.
I bet you can’t pronounce half the marine names you’re posting though 😉