After about 5 weeks of wondering if the strange look of my BTA was what I thought it was... it has split!
I had mentioned my suspicions to a couple of folks in the chat room last month and posted a really pitiful picutre of what I suspected to be my nem in the process of splitting. It was very hard to tell since it was hanging from the roof of a cave. It had stopped accepting food, and then I stopped even trying to feed it because I could see the mouth was incomplete, like a stretched out "C" shape.
This morning, I found the "daughter" creeping out of the cave. I quickly moved the corals in her path, and I will be keeping a very close watch on her until she settles in, rearranging the other inhabitants until that time comes.
Maybe I will leave Marlin and the 2 nems in the 10g (along with the hermits and shrimp) after I have moved the other critters over to the new tank. I don't know... maybe I'll take the new nem into my LFS for credit.