Could be berghia but difficult to tell from that angle. Curious to know if it hitchhiked on a frag or how it got into your DT. If it is a berghia it will look for aptasia but if you have none, it will just starve & wither away.
Nice! I didn't realize you had purchase some. Makes sense LOL
Zoa nudis usually are more tan and take the color of the zoas they are eating. Monti nudis are more white colored like your picture but are usually pretty small compared to berghias.
No never purchased them. They ridiculously expensive and too small. 2 of then are about .5" and 1 is maybe 1" when it crawl on the back wall. Is there a chane they stay deep in rock and now finally show up cause they hungry lol.