Any ideas on this?

[Raven k]

Found this on my live rock and I have no idea what it is, does anyone know?

 

[WalkerLoves_TheOcean]

Is it moving around the tank or is it stationary?

 

[Raven k]

Is it moving around the tank or is it stationary?

It’s stationary

 

[WalkerLoves_TheOcean]

It’s stationary

Hmm, I don't really know then, the pictures aren't that great, I have to go to work, but I will think about it during the day.

 

[Troylee]

Appears to be a sponge.

 

[Raven k]

Hmm, I don't really know then, the pictures aren't that great, I have to go to work, but I will think about it during the day.

Thanks, even with the magnifying glass that’s the best I can get. It seems to be a blob with long tentacles? Sticking out of it that have little round bits mid tentacle. Here’s a very crude sketch

 

[Raven k]

Appears to be a sponge.

I do hope so, closest thing I’ve found so far is pineapple sponge but it’s not quite right

 

[Troylee]

I do hope so, closest thing I’ve found so far is pineapple sponge but it’s not quite right

If not it’s a tunicate.. harmless either way.

 

[Reefkeepers Archive]

Pineapple sponge

 

[Raven k]

Thank you guys, harmless is good news

 

[Reefkeepers Archive]

When they're in low-no flow environments I've noticed they develop spines (upper center, circled in red)

 

[Raven k]

When they're in low-no flow environments I've noticed they develop spines (upper center, circled in red)

It is tucked around the back in a low flow spot

 

[Tired]

Oh, huh, I haven't seen my pineapple sponges do that. Neat.

OP, a better photo would help confirm, but it's likely to be some sort of sponge, if not a pineapple.
(edit for clarity: probably spiky pineapple. Maybe some other sponge.)

 

[ISpeakForTheSeas]

Appears to be a sponge.

Looks like a Tethya species to me:

Looks like it may be Tethya gracilis - it should be a harmless filter feeder.

They're not super well known (they were discovered first in a German aquarium), but the study I've found describing them was very informative (linked below).

They grow up to ~1.5cm (though they can contract to be ~80% of their max body size); they can slowly move/"walk" - reportedly, they can move several centimeters a day (especially when smaller), and they do this to remove/shake off sediment that gets on them; and they reproduce by budding (so they'll drop pieces that grow into new sponges).

https://www.researchgate.net/publication/215665065_Three_New_Species_of_Tethya_Porifera_Demospongiae_from_German_Aquaria

 

[Reefkeepers Archive]

Looks like a Tethya species to me:

Now that you mention it you're probably right, the flesh texture looked alittle off to me