Nudi?

[brynnie]

Hello!! I just got some new corals and found this little guy, is he a good or not good for a reef tank?

 

[Sophie"s mom]

Not sure! Maybe @ISpeakForTheSeas can come in and comment on this one.

 

[ISpeakForTheSeas]

Not sure! Maybe @ISpeakForTheSeas can come in and comment on this one.

Good guy: Elysia sp. Sacoglossan Slug (A.K.A. a Lettuce "Nudibranch"), and it's an herbivore - if it's from the Atlantic, it's E. flava; if it's from the Pacific, it's E. obtusa

Elysia flava or E. obtusa - harmless/beneficial Sacoglossan slugs. They're herbivores, with E. obtusa known to feed on Bryopsis, while E. Flava is thought to feed on Cladophora.

it seems at least some adults of some species can survive feeding on algae that isn't their preferred food, but juveniles cannot

If you don't have access to their preferred feeds, you can try some of the below or another green algae, but no guarantees they'll feed on it/derive adequate nutrition from it:

Elysia slugs generally feed on siphonalean algae such as Caulerpa, Codium, Acetabularia, Halimeda, Udotea, Byropsis, and Valonia spp.