id pulsating jelly thing

[theedprado]

i have a bunch of top hat shaped pulsating translucent things swimming around in my tank they are about 1/8 of an inch in diameter. anyone know what they are?

[GaryP]

Not without a picture.

Gary

[Instar]

They are a medusa larval stage for another animal and/or one of the animals that makes up the zoo plankton and are related in their functions to jelly fish. Occassionally one will attach to the glass and get larger. Often they attach to the glass and don't grow. Their tentacles sting like crazy if they do grow but, normally they don't do anything in an aquarium. New tanks or very high water quality usually will produce them. Mostly they go unnoticed. I never seen them turn into anything really cool like a coral or something and I think they either live out their lives or get consumed by plankton eating creatures. They are very common and very damaging in a hatchery as they kill baby seahorses and larval fish.

[Tim Marvin]

Yes, I have had tons of them from time to time.