Sure looks like a sponge and will spread and could bother and cover close by coral. If its spongy and the hole in the center or mouth closes whene removed from the water i would say it is a sponge. Much easier to controll at this point. I would give it a RO
water no salt dip or a fresh water dip and use an wire brush to remove. I use an automotive brush , a smaller one from checker. They have a 3 pack and the brush head is about 1 1/2 inches long. Setup a coral station with everything needed. A bowl of tank water , bowl of fresh water. Use the tank water to rinse off befoer adding back to the tank.
If you do have frags on it then i would just remove them and glue to a frag plu or rubble rock and discard the small frag.