What is it?

I know it's a snail, but I want to know the species and whether it's beneficial or a pest before I go on a squishing rampage, I've spotted maybe 7 of them in my tank over the last day or two, and this one's the largest (so far). I've only intentionally put ramshorns and MTS in there so I'm lost...you can see an MTS to the right for size comparison, the stranger's the smooth guy to the left. Thanks!

Thanks! I'll squish every one I find from here on out . It's appx. 2/3 sandblasting sand, 1/3 eco-complete, and a couple handfuls of crushed coral to help keep my pH stable (I live in a soft water area) all mixed together. The plants and fish love it too

The food thing would explain why they're showing up now but hadn't earlier if a couple were in hiding...my husband seriously over-fed while I was gone for a week and I came back to a layer of molding flakes on the sand and brown hairy algae on the decos...yesterday I vacuumed and waterchanged and stirred the sand and cleaned the decos and glass and vacuumed/WC some more, but I'm sure I didn't get everything and they had a week to feast. Yuck. I thought about loaches but my tank's only 46G and I don't want to get attached and then have to trade them in later (and my apartment's too small to accomodate a larger tank). I have some kuhlis, but they don't seem to be interested in snails