Got some Thiara winteri snails from Bob. Never had snails before. Just noticed these tooth-like protrusions around its "collar" if you will. Looks like the teeth/mouth of a sci-fi killer worm.
Yes, all the trumpet-shaped snails have them. As to what they are... I did a bit of searching and couldn't come up with an anatomical term. How about "shell grippers"?
Interesting, if technical, article on Wikipedia about shells, formation of same, names of the structures and so on. You might find it interesting. Let me go find the bookmark.