Did I just find a jelly in my tank???

I saw this little guy pulsating around in my aquarium and captured him (just in case, ya know...) I took some pictures and a video for reference. Upon googling, I found this:

http://www.thereeftank.com/forums/f6/what-the-heck-jellyfish-id-anyone-137067.html

Mine is somewhat similar, except a light tan color, I have no others (that I can see) on my glass or rocks, and instead of "8 thin tentacles", mine has more of an umbrella-type top. It likes to pulsate around for a bit, and then sink to the bottom and sit on its head, sort of like the upside-down jellyfish, cassiopea.

I have no idea what to think of it (except that it's kinda awesome). Should I take it out? Keep it in? Will it sting my fish? Scott already tried to eat it before I shoo-ed him away when it briefly escaped my container. What if he succeeds?

Here's some pics. I have him in a 10mL beaker. He's no bigger than a pencil eraser. I also have a video, but I dont know how to put it on here.

Looks like a wittle Jelly to me. Wow it's cool how tiny it is !

The pictures wouldn't have made a bad PotM for the close up theme!

Farfromfiji wrote:

The pictures wouldn't have made a bad PotM for the close up theme!

Hahaha, Im always late getting to things.

I found this online:
http://www.wetwebmedia.com/jellyidfaqs.htm
On 10/31/09 a guy had something similar (and better pictures) and they think it's a hydrozoan medusae
I do have similar looking polyp things in my tank, but I always assummed they were feather duster sorta things. I've had them for ages and never seen a medusa.

hmm that's really cool!

wonder when he could've gotten in?

Definitely looks like a jelly, and I think you're right about it being a hydrozoan medusae.

Seems like this WWM post is most relevant...

- - - - -
Hydrozoan medusae: mystery solved? -- 10/31/09
Hello Dear crew,
I just wanted to share a bit of a mystery that kept me going crazy for many months.
<Oh! Please do>
There were two observations that I could not resolve with regard to identity. First, I kept seeing these little jelly fish-like creatures that occasionally appeared in my reef aquarium, and that mysteriously disappeared after a while. Second, there were these other creatures that looked sort of like little worm dusters, but clearly there were not dusters as they did not retract their crown when disturbed. After staring and poking into my aquarium for many months, and searching to no avail, I think I have it! The jelly fish are the
medusa stage of a Hydrozoan, and the "feather dusters" are the mature stage of the Hydrozoan (please see attached pic)!
<Nice work>
Please correct me if I am wrong.
<You are not wrong>
I am delighted that I seem to have finally made an ID, but of course not that happy that I have
hydrozoans all over my rocks. Is there anything that eats them?
<Mmmm, not specifically, no>
I do not want them to sting my corals!
<Best to keep filtering them out... eventually their source will be exhausted>
In any case, I just wanted to share the pictures as I could not easily find the info in the web, and it took quite a bit to reach the above conclusion. I hope this can be of help to others, having mystery jelly fish roaming their reefs.
Best,
Vivian
<Thank you for sharing! Bob Fenner>


- - - - -

I would take the advise of WWM and get them out of your aquarium. They're pretty cool, though! Maybe set up a separate small aquarium for them...?

Oh, P.S., to upload a video...

1. First, upload it to Youtube
2. Then, in the forum's post area (once you click "preview"), click on the icon that looks like a filmstrip and paste the Youtube URL.

I don't have a youtube or dailymotion account. Are those the only ways to do it?

I believe so. I ended up making a Youtube account. It's simple.

That's pretty cool.. do upsidedown jellies even sting much?

This isn't an upsidedown jelly (though I was initially concerned about that since we had handled them in lab earlier that week) To answer the question though, they do sting to catch prey but they also rely heavily on their zooxanthellae, so their sting isn't developed to be very strong. It probably wouldn't bother a human other than a bit of redness in a sensitive area like the face, unless you're allergic or something. I don't know how their sting affects a small fish or other corals and that's what Im concerned about with this guy.

By the way, I decided to keep him. I put him in that beaker with plastic over the top. I poked holes so there's some, though little, water exchange. But no food really goes in there, so I dont anticipate him living long. I really just want to see if he turns into a polyp...

that thing looks like a medusa but then again it has the traits of a jellyfish in my opinion i thinks its a medusa but on the other hand i wonder if you could set it up in a jellyfish tank that would be cool and maybe breed those things now that would be cool i think its a medusa