I’d please

[basementreef]

Found during coral QT

 

[ISpeakForTheSeas]

Looks like it's probably an Elysia sp. sacoglossan slug - algae eater:

Some lettuce slugs (typically from the genus Elysia) will eat nuisance algae species, but their wild diet varies pretty drastically from one species to another, and some species have some pretty specific wild diets (I don’t know if these are required diets or preferred diets, but Reef Cleaners reports that they'll eat just about any green, fleshy algae). That said, Elysia slugs generally feed on siphonalean algae such as Caulerpa, Codium, Acetabularia, Halimeda, Udotea, Byropsis, and Valonia spp. So, in theory, these guys should eat nuisance algae that pops up in your tank.

 

[basementreef]

Keep it?

 

[ISpeakForTheSeas]

Keep it?

Unless you're running a macroalgae tank, yes.