Can anyone help I'd what's on my snail?

IME, Mermaid's cup tends to not do fabulously in super "clean" water, such as in a reef, so don't fret if it disappears. They are very cool-looking macro, at any rate.

Let us know how it's doing.

 

Additional pictures of my .5 gallon experiment

Additional pics... it really isn't that impressive. I need more coral and need some help in what may do well. This was an experiment . Basically to show my son it could be done. He has an amazing reef tank. 2 years later with an early die off of some mushroom I was told were impossible to kill, it seems to be doing pretty well. Dont laugh... its running off of an old air pump driven sponge dirt magnet , has a small heater and a reef light hanging over it. Thats it. Every couple weeks or so I do a 1/4 water change and I squirt a little Phyto Feast a couple times a month. And yes I live in NJ and it stays by that sliding door all winter long!

 

Cool your own little tide pool.