Yes, looks like Majanos.
Very hard to eliminate. I ended up rebooting my tank to rid the infestation.
Key things:
Kill them with usual aptasia-x or other chemicals manually as best you can.
Try to keep them below "critical mass" or they explode in number.
Feed less. Definitely no flake food.
Matted filefish do eat them, but not always, and is not all that reef safe.
I would even screw around, remove the rocks that have them, chip off the pieces of rocks with them on, get used to re-aquascaping a few times in the coming months.