Help ID creature on my snail

[Luis_Rosario]

I bought this Astraea snail a couple of weeks ago I noticed something on it but it was way smaller today it’s a lot bigger just wondering if it’s good or bad

 

[vetteguy53081]

I bought this Astraea snail a couple of weeks ago I noticed something on it but it was way smaller today it’s a lot bigger just wondering if it’s good or bad

Looks like a collanista snail with coraline on its shell
Try twisting it gently to separate them

 

[Crabs McJones]

Slipper Limpet. Harmless