What is this

[whasamada]

I have a mini hospital tank i keep on standby. I saw this thing flittering in the tank. It only moves when disturbed, it moves kinda like a jellyfish then settles and sits on the bottom. What is this?

 

[Privateye]

It could be a hydroid of some kind. This is the "medusa" stage of a cnidarian. Jellyfish are another example of a medusa stage, but a different cnidarian.

It's unlikely that this is a true jellyfish. When I had something similar I attributed it to a hydroid. Either way, I never saw any cnidarians in the tank (other than my corals) other than this medusa stage. I don't believe it survived.

 

[BryanM]

@ISpeakForTheSeas