Thing growing on my hermit

[Babymama18301]

I had bought this cub off some one from Craigslist a while back the lady said that they had once had marine velvet in the tank, but was all gone now. she had some sad story so i didint even try talk her down. payed 200$ for it and it included 20lbs lr 20lb ls a harlequin shrimp cleaner shrimp, torch coral, a couple other corals food cleaning stuff and a few other things
and noticed this thing growing on one of the hermit carbs. Also on one the snails there like this lil shell attached to it n when the snail cleans the glass the lil shell has a black thing that comes out and attached to the glass as well. I don't have a pic of the snail but I do the hermit.