Snails on Snails!

Hello

My Turbo Snails seem to have other much smaller snails on there shell...

At first I though they were babies as they seem to multiply all the time in
my tank but there a much whiter colour than all the babies on the glass and
there a much slimmer shape (like hermit crab shells).

They don¹t seem to be bothering the snails as there still munching away and
are also not going near the snails soft tissue but rather staying on the
lower and underside of it

Any ideas

Thanks in advance

Warren