Nudibranch? Slug? Harmful?

[Lawmanrich]

Saw two of these guys in my DT. Do I need to get em out when I see em and what are they?

 

[reef lover]

Looks like a type of elysia they are fine.

 

[Lovemyreef2015]

It's a Elysia slug. They eat Filamentous algae and Caulerpa.