Snails need shells?

[no_Wedge]

I just got 7 nerite snails, and 3 are very small, while 4 seem to be full size. I was wondering if you are supposed to get empty shells for snails so they can change or grow?

 

[LeslieH]

Shells are continuously produced & enlarged by the animals inside. It's hermit crabs that need empty shells for housing.