snail with out a shell?

I dont know how to post pix or i would have posted it

 

I noticed one of these in my tank a couple of weeks. It was not large nor small. However, the last few nights I have seen 3,4 smaller ones on the glass. What is funny, is that the other night I noticed the larger one was on top of one of my Nassarius snails as if it was trying to devour it. I pointed the flash light at him and he moved away quickly. I know they are algae eaters, but should I be worried that they may attack my snails. They are not that good looking either so I would not want to have them multiply so quickly. Any ideas?

 

Eating algae off the nassaruis shell. I would be more worried the nassarius would eat the stomatella. They are whelks at the end of the day.

 

How to post a pic: When you are posting, go to "additional options" further down the page, then click on "manage attachments". A new window will come up, click on "browse" and then go to the folder where you have the pic you want, click on that pic, (repeat the process if you want to add more pics) then click on upload. When they have uploaded click on "submit reply".

 

Here are the pics. They arent the best but hopefully you will see what im talking about.

 

And thanks accent ive been wanting to figure out how to upload for a while now.