The rock came with 2 legit BTA's on it, but from a system that also had a majano problem so I figured the top one had to be a majano. As for the white one, I thought the foot seemed way too long to be a BTA given how small the head is, but I'm no expert.
Any other opinions?
I was going to let them grow regardless just for kicks. I'm not adding that rock to my system, it'll stay where it is for a fun critter tank. There are some asterina stars, bristle worms and a bunch of brittle stars as well in there.