This big guy is a calumniating brown macro algae
They are apparently tricky to get
(mine randomly started growing in the tank and now its every ware)
macro algae feeds of harmful nitrogen and converts it into nitrates which are safer for the aquarium
This guy in particular is special because it actually gathers calcium out of the water and grows a bone like shell
Enabling it to have these rigid fantastic spirals
And it wont guy stung to hell by some of my more aggressive corals and anemones