Please help me ID this!

[LamboBoy]

This almost transparent thing is all over my refugium and on the gravel of my main tank.

It looks like some kind of worm, it is definitely alive because it retracts when touched. Need to know what it is to see if it's harmful to fish. Tank is in it's 4th week of going fallow.

 

[LamboBoy]

Anyone?? Anyone out there??

 

[LukFox]

Really small digitate hydroids? Mine are bigger than that, but they look the same in shape and behavior.

Mine:

Not harmful to fish, but MIGHT sting nearby corals. Mine haven't caused any problems.

 

[LamboBoy]

Really small digitate hydroids? Mine are bigger than that, but they look the same in shape and behavior.

Mine:

Are you sure they are not worms??? Yours look different to me, more spikes sticking out..... my looks rounder.

Not harmful to fish, but MIGHT sting nearby corals. Mine haven't caused any problems.

 

[LamboBoy]

After looking at my pics under 200% magnification, you are right, my looks just like yours.... thanks for your advice.

So they are harmless?

 

[LukFox]

The spikes are retractable (probably feeding mode when they're extended), and those shots are pretty zoomed in.

Some zoomed out shots from google: http://media.photobucket.com/image/digitate hydroids/icenine2006/DSCN0176.jpg and http://www.mikesreef.com/images/critters/Hitchhiker17.jpg The shape in your photos looks similar to me, but you'd know better of course seeing them in person.

[edit] You posted when I was typing . Harmless to fish, yes. If they're covering a rock used by an eel it might be cause for concern due to exposure time and density, but their thick slime coat might be enough to protect them anyway. I mess with my algae all the time (the hydriods are all in there) and even I've never been stung. My fish have never shown any irritation. IME they're quite harmless, and when I asked the forums about them they didn't seem to be causing problems for others' fish either.

 

[LamboBoy]

The spikes are retractable (probably feeding mode when they're extended), and those shots are pretty zoomed in.

Some zoomed out shots from google: http://media.photobucket.com/image/digitate hydroids/icenine2006/DSCN0176.jpg and http://www.mikesreef.com/images/critters/Hitchhiker17.jpg The shape in your photos looks similar to me, but you'd know better of course seeing them in person.

[edit] You posted when I was typing . Harmless to fish, yes. If they're covering a rock used by an eel it might be cause for concern due to exposure time and density, but their thick slime coat might be enough to protect them anyway. I mess with my algae all the time (the hydriods are all in there) and even I've never been stung. My fish have never shown any irritation. IME they're quite harmless, and when I asked the forums about them they didn't seem to be causing problems for others' fish either.

Thanks for your advice, I'm now sure they are what you described.
I guess I'll just leave them alone!