Hi LemonLemon,
I am pretty sure its not shredding.
The "fine tentacles" look-a-like are from the bottom of the coral, not the top. I wasn't able to capture a high defination video but its definitely trying to catch something. The moment it touches some "dust" it will retract back for a while, then release the "thing" out to flow again. The "thing" looks like a feather and can be extended a pretty good distance and retract back again. Very interesting to watch!