What are these white tentacles?

[johnf3]

I recently purchased a nice purple nephthea coral and just now noticed these white tentacles that have grown from the rock since I got it. I don’t remember seeing them when I put it in the tank so I’m pretty sure they’ve grown over the past month. Very curious as to what these are/ this is?

 

[Timfish]

My guess would be some kind of sponge. They are capable of growing very fast under the right conditions. But there are various organisms that make tubes. I'd consider them beneficial.

 

[DaJMasta]

Do they flow, or do they mostly have the same shape/direction/thickness? If they're more static, I'd agree probably a sponge.

 

[johnf3]

My guess would be some kind of sponge. They are capable of growing very fast under the right conditions. But there are various organisms that make tubes. I'd consider them beneficial.

Alright thanks, they are definitely non-photosynthetic so a form of sponge would make sense. I know the guy I bought the coral from directly imports his stuff and doesn’t dip his nephtheas so it really could be anything. Doesn’t seem to be doing any harm, just curious/excited to find something new in the tank!

 

[johnf3]

Do they flow, or do they mostly have the same shape/direction/thickness? If they're more static, I'd agree probably a sponge.

No they flow like anemone tentacles. I haven’t touched them but they appear to be squishy

 

[DaJMasta]

Interesting, do they retract and extend at all? Do they react to touch?

 

[johnf3]

Interesting, do they retract and extend at all? Do they react to touch?

Just touched them and they don’t react at all. Haven’t noticed them get any longer/shorter either.
They are very thin tissue and when you squeeze they go flat for a second and then re-inflate. Each has a separate base connected to the rock

 

[Timfish]

Alright thanks, they are definitely non-photosynthetic so a form of sponge would make sense. I know the guy I bought the coral from directly imports his stuff and doesn’t dip his nephtheas so it really could be anything. Doesn’t seem to be doing any harm, just curious/excited to find something new in the tank!

I'd say they very beneficial. Sponges are essential recyclers on reef systems and there's only one or two species of light loving sponge that might be an issue for aquarsts.