Reef Discussion

[Felicity goodall]

Hello all, I recently found this snail in my tank. It was not one I introduced and I was told to bin it. Is this one good or bad and what is it.
ALSO I found a baby snail that looks similar but I don't know if it is just what young cerith. Most of my ceriths are black.
I have a pic of the so called bad one only

 

[Oceanarium]

Bad boy, coralivour.

 

[Felicity goodall]

Ok here is a baby and an adult that I bought. Is the baby from the adult?

 

[Oceanarium]

Looks like it is likely be a baby Cerith. Bit hard to tell from the picture so cant be sure.