Bristle worms making a ?? who knows.

The pictures say it all.
I took a few things from my tank and found bristle worms creating what looked like a resin structure in two spots.
The substance they made is not a brittle as coral, but is as hard.
I left what they made out for three days, then put them back into the water, they both developed a skin as does any dead tissue, this stuff was alive or made by life.
Certainly strange!
The small one with the worms hugging it closely.


After I took them off it.


The lager structure with worms still on it.


The structure once worms are removed


The oceans life are certainly diverse, and at times, quite interesting!