*UPDATED: PICS* Snail with THING on its butt!!

[girlm]

:hi: I have had fish before, but only betas and some fancy goldfish, and now I have a 3month established tank and am totally clueless. I've always wanted a sw tank and I finally got one for my b-day. My fiancé set everything up and was capable of taking care of it. Me, I just wanted it because they're beautiful and have a great calming effect on me. Fast-forward a bit.... I no longer have a fiancé and I've gotta handle the upkeep. I'm totally fine with it. But....like I said, I'm totally clueless. Im coming to these forums like a little kid....what's this, how does that work, is this normal.....so bare with me hahahaha
Main reason I'm seeking help today at least......I have a snail with a thing on its butt!!!! :%%: I've added pictures below. The holes/openings sometimes open and close. Gross I know!!! I'm really worried. If anyone knows what this is, please help...!
Thanks

 

[snakeblitz33]

Welcome to the forums!
I have absolutely no idea how this thread got away from me! Please come back and stay awhile, we really are good people, it just sometimes takes us a little while to respond to everything!
Here's a good start if you want to seriously take care of a saltwater tank:
https://forums.saltwaterfish.com/t/388776/guides-for-new-hobbyists
I would say that you have a sea squirt on the snail, or some kind of tunicate. Harmless...