Pulsing critter ID help?

[Papai]

Can anyone help ID these pulsing little guys? They were smaller and free floating and eventually attached to the PVC pipe in my QT tank. Looks like some babies attached to glass too. Finally, there were more hiding under my rock-work in my Display tank too! Are they a pest to be removed? Thanks for any help!

 

[mtfish]

Looks like some type of stalked jellyfish. I do not have any first hand knowledge about them. I think they are cool and would leave them be if it were my tank. I like to watch weird stuff that can end up in our glass boxes.

 

[eggplantparrot]

upside down jellyfish maybe?

 

[F i s h y]

Hydroid

 

[F i s h y]

They have a free swimming life stage that appears like a jelly

 

[Papai]

They have a free swimming life stage that appears like a jelly

Thanks, I've been researching both jellies and hydroids and the hydroids all seem to have tubular stalks, more like skinny squids. These seem more like Jellies, but it's strange that after their free-swimming stage they have attached to either sand-bed or the PVC pictured here in my QT.

 

[Papai]

Looks like some type of stalked jellyfish. I do not have any first hand knowledge about them. I think they are cool and would leave them be if it were my tank. I like to watch weird stuff that can end up in our glass boxes.

Thx, I think they are cool too and would prefer to keep, but want to make sure they are not a danger to my other livestock, especially the juvenile Yellow Tang that's in with them in this QT tank that's not big enough to go in my display yet. Never heard of upside down Jellies. And these are not free swimming anymore. They were at first, when smaller, then attached.