What are these?

[jthunderzzz]

I just noticed these little slug things on one of my rocks. Does anyone know what they are and if they are good or bad?

 

[shakacuz]

nudibranch but i have no clue which. it’s only black and yellow? maybe: https://nudibranchdomain.org/produc...s nudibranch vespa,had been called Casella sp.

 

[jthunderzzz]

nudibranch but i have no clue which. it’s only black and yellow? maybe: https://nudibranchdomain.org/product/glossodoris-vespa/#:~:text=Rudman named this nudibranch vespa,had been called Casella sp.

They aren’t bad then right?

 

[shakacuz]

They aren’t bad then right?

i’m very unsure. there are so many different species of nudibranch. i googled it based on the colors i saw in your pictures

 

[jthunderzzz]

i’m very unsure. there are so many different species of nudibranch. i googled it based on the colors i saw in your pictures

Ok, thanks for looking I have googled too and am having trouble narrowing it down too lol

 

[tmm161]

What would these possibly be.

 

[ISpeakForTheSeas]

What would these possibly be.

Are you asking about the things with shells that appear to bivalves of some kind? Because it looks to me like a couple of bivalves with the mouth/mouths (the fleshy parts) circled.

If not, you may need some clearer pics for an ID.

 

[Brit’s Fish]

Ok, thanks for looking I have googled too and am having trouble narrowing it down too lol

I believe they’re the good guys. They’ve been popping up more often lately - Elysia obtusa maybe? @ISpeakForTheSeas identified these guys for me when I found them in one of my tanks. They’re algae eaters.

 

[ISpeakForTheSeas]

I just noticed these little slug things on one of my rocks. Does anyone know what they are and if they are good or bad?

These are probably Elysia sp. sacoglossan slugs like E. flava or E. obtusa - algae eaters:

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. As mentioned below, I don't know if these are required feeds or just strongly preferred feeds:

 

[tmm161]

They have not moved. Never. just gained size.