Can someone ID this?

[ivysbe]

Hello! So to start this off, this is my first post on the forum so I apologize if whatever this is has already been identified. That being said, I've recently started my first saltwater tank and it's just now starting to mature. Over the past few weeks, I've noticed these critters on my live rock and on the glass near the heater (I've attached images.) I'm assuming they came in from my zoas that I bought ~2 months ago (from a trustworthy LFS), but I don't have any other ideas as to where it came from. All fish and corals seem to be fine and water parameters are good. They don't seem to be causing any issues, but they do seem to be multiplying over the past few weeks. If possible can someone ID these for me and let me know the best course of action to get rid of them, I would eternally grateful. Like I said, I'm pretty new to saltwater stuff so it's definitely kind of strange to see random, unidentifiable creatures appearing in your tank! Thanks!

(Also, I can turn on the white lights and get some more pictures if needed)

 

[Brittany Marie]

Pineapple sponge. Good to have. Means your tank is doing well!

 

[vetteguy53081]

They grow in shaded area and can be evasive especially if you feel coral foods as they’re filter feeders
Good news is that they’re not long lived
They’re also capable of choking out some corals so keep an eye on their growth

 

[Brittany Marie]

Sorry I should’ve added some helpful info. I’ve had only a handful in my display but huge congregations in my sump and canister filters. I think some other creatures must’ve kept them under control in the tank. I never did anything about them, because extra filtration. But like @vetteguy53081 said if they start to infest your display I’d take action

 

[Spieg]

Look a bit like nudibranchs to me... do they move around or just stay in one spot?

 

[vetteguy53081]

Sorry I should’ve added some helpful info. I’ve had only a handful in my display but huge congregations in my sump and canister filters. I think some other creatures must’ve kept them under control in the tank. I never did anything about them, because extra filtration. But like @vetteguy53081 said if they start to infest your display I’d take action

There really aren’t any predators for them
They slowly vanish

 

[Brittany Marie]

There really aren’t any predators for them
They slowly vanish

Good to know! I don’t mind them. I actually think they’re pretty. It’s these stupid little sea stars my fight is with

 

[vetteguy53081]

Good to know! I don’t mind them. I actually think they’re pretty. It’s these stupid little sea stars my fight is with

Get rid of those by hand or net daily
They multiply like mice and eat zoa and other coral

 

[Brittany Marie]

Get rid of those by hand or net daily
They multiply like mice and eat zoa and other coral

Yeah I don’t have corals anymore. But I pull them out when I see them an throw them in a little container to dry out and put in my curio cabinet.