No idea

[Jimboaf]

I have no idea what these things are, I will try to describe them as much as I can. They seem to start out as a jellyfish type thing that sometimes suck to the glass and seem to have tenticals. They I see some swimming around in the water column. Then they seem to just sit on the sand bed. I have no idea what they are attached is a picture and I circled them.

 

[reefnoob]

I've recently had those too! In my tank they like to swim near the surface.

 

[Mandarin66]

From that picture it look like spiders

 

[Salty B]

Hydroids...some say harmless, some say they gotta go. I'd say leave them alone and they will go away when their food source is used up.
check here...http://www.chucksaddiction.com/hitchodds.html

 

[Mandarin66]

The one on the right look like a 4 leg cricket

 

[Bifferwine]

+1 Salty. I say they are harmless.

 

[reefnoob]

Mine aren't attached to anything. They swim around in the jerking motions like jellyfish do.

 

[Jimboaf]

Yea when I did a water change yesterday, I saw like hundreds of them at the top of the water swimming around. I must have thousands in my tank, I am kinda afraid to put my hands in there I might get stung. Still have no idea what they are

 

[Bifferwine]

They are hydroids. Not the colonial kind that grow on rocks. Free-swimming hydroids.

 

[Bifferwine]

Indo Pacific Hitch Hikers

Scroll down the page a little bit to read about them.

 

[Jimboaf]

Yea, they seem to be exactly like the first and second picture in the The Jellyfish Cladonema sp. I been trying to research them online but nothing except for that picture. I did try to take some of them out yesterday with the water change.