Identification question

[Guillaume]

Hello Folks,

I just discovered this Slug/nudibranch in my tank.

Does anyone know what it is? Is it good or bad? A nudibranch or another species? It is 1 cm long at the moment.

Thanks for yor help

Guillaume

 

[LeslieH]

It's a sacoglossan which means it's not a nudibranch and it's an algae eater.

 

[greenbean36191]

It's a species of Elysia, but I couldn't begin to tell you what it will eat other than some sort of green macroalgae.