What kind of snail is this?

[jaws789832]

Its like a cross between a snail and a slug. All I know is I didn't put him there so is he good or bad?

he is about the size of a dime

 

[jaws789832]

The black thing on top is his shell. its the shape of a scallop shell. the brown underneath is his body all soft and slug like

 

[Quah]

It is a Stomatella snail they are beneficial and harmless and will reproduce in your aquarium. Some come with really nice coloration like a sky blue shell and a black body. Let it become part of your CUC and you'll both be better off.