What is it, pls?

[Celine]

This little guy comes along w/ my new coral.
Good? Bad? It looks like a snail w/ a shell.

Thanks in advance.

 

[Robbiesamp]

I don't know I have around 5 but they seem good so I'm just going to leave them

 

[Celine]

I got to be more careful. Lately, I found a lot of strange stuffs in the tank , no clue where they come from.