Jellyfish!?!?!?!?!
 

I just found a little tiny ( like the size of 4 or 5 grains of sand) jellyfish in my tank I took him out with a pipette and he is living in a cup right now. Are these bad? what should I do with him?

Might as well put them back in the tank, they're harmless. Unfortunately they won't amount to much though, take a picture if you can and enjoy the moment is about all you can do. Many creatures have a juvenile stage in a hydroid phase. It could be crab larva, polyps ... some kind of invertebrate anyhow, no real way to know for sure.

I thought I had myself a jellyfish. It really looks like a jellyfish ( looked at it through a magnifying glass) but if it is not I wonder what it will turn into. It is so cool to watch it just kinda swims around aimlessly!

well... technically any crustacean larvae are called nauplii tony :)

hydroids and cnidarians can have what is known as a medusa stage. the medusa looks like what most people know as a jelly; hydroid medusae are called hydromedusae and look very similar but have a few mostly anatomical differences. All of them have a polyp stage. medusae are supposed to settle and make a new polyp but I highly doubt that they can accomplish this in captivity unless special precautions are taken.

in the end though the result is the same; it will get eaten or chopped in a pump, either way it will die without causing any harm.

I found two more today and put them in a baby guppy holder but one of them escaped and my firefish ate it! :( I think (if these guys arent jellyfish) if the one I have in the holder ever stops pulsing and settle it will have no problem developing because the baby guppy holder is made of hard plastic.

Years ago, I had several medusa-stage "Jellies" pop up in my seahorse tank. As many as four or five at a time. They were really cool & one of the reasons sw tanks are more fascinating to me than fw. All sorts of cool hitchhikers & unexpected biodiversity in our tanks.

Anthony

Oops, said hydroid stage but meant medusa..

I did take nearly a minor in bio but I'm old so it was a long time ago. Cut me some slack you dang whipper snapper :p

Found 3 more "Jellies" today and they were all being eaten by hydra. I have a lot of hydra in my tank they live in the cracks that the hermit crabs cant get to to eat them. Is there anything I can get that will eat the hydra?

If I'm correct the phylum cnidaria also contains Anthozoa (The corals in our tanks) which do not have a medusa stage. As for the not causing harm thing, im sure 95% of the cnidarian species in our tanks are harmless but I have seen Jellyfish completley wipe out a sea horse tank.
Levi

About 10 or 12 years ago when I had my first reef tank I had a large amount of little "jellyfish". I seemed to think they came from little creatures that looked like mini feather dusters, but that was so long ago that my memory only serves me the way that I recognised it then. If I knew what I know now, I think I would have been able to identify the mini feather duster things, and probably come to the conclusion that the "jellyfish weren't coming from them. Who knows! But the "jellyfish" I had only came out after lights off, and they filled the tank probably 1 "jellyfish" per 2-3 cubic inches of water. I remember very clearly that there were a lot of them. I didn't have much for pumps to kill them though, as back in those days all I had was an undergravel filter, and an AquaClear HOB filter. :o