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Small, jelly-like leggy swimmers ?


eolith

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20140224-01-crop.jpg
I found these guys today when I shut off the pumps to do my usual feeding. I have identified 3 separate individuals. They apparently get swept away when I turn my pumps on, but in still water, they are decently mobile. They're 1-2cm across when immobile. They swim kind of like a jellyfish, flexing all their little legs at once.

 

The body is not like a jelly fish, it just swims like one. The body is kind of a dark-brown/black peg that sticks up from perpendicular to whatever surface they're sitting on.


These are videos from my cell phone, pardon the quality and the file size.

10MB - In the middle of the screen, you'll see one of them launch and float down.
http://www.exile-guild.com/eolithics/images/aquarium/jellyswimmer/20140224-Swimmer-Middle.mp4


5MB - Here's the little guy falling after swimming upward:
http://www.exile-guild.com/eolithics/images/aquarium/jellyswimmer/20140224-Swimmer-Falling.mp4

80MB - You can see him swim just to the right of the cerith snail in the foreground. He looks like a black peg until he swims at about 00:32:
http://www.exile-guild.com/eolithics/images/aquarium/jellyswimmer/20140224-Swimmer-Front.mp4

250MB - Right at 00:57, the swimmer is in the open white part of the snail shell in the background, you can see a small black peg launch momentarily and then land.
http://www.exile-guild.com/eolithics/images/aquarium/jellyswimmer/2040224-Swimmer-Back.mp4

 

Youtube video of the 10mb "middle" file above (available in 720p):

 

Another video, in 1080p:

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I can't see the pic or vids but based on description I'd place money on them being the free swimming (medusa?) stage of hydroids..

 

most people consider them a pest (supposedly stinging zoas and stuff), but I've never had a problem with mine and I think I have two different species.. neat creature..

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The body is not like a jelly fish, it just swims like one. The body is kind of a dark-brown/black peg that sticks up from perpendicular to whatever surface they're sitting on.

 

From what I'm seeing of the hydroid images, they're more gelatinous, with transparent shells like a jellyfish.

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Polarcollision

yep! That is the free-swimming stage of hydroid. When they establish somewhere, you'll see white hair-like strings that stretch out and then retract toward the base. They're not a huge problem, other than stinging corals. My zoas don't grow as well when they're next to them. Come to think of it, I haven't seen them since I installed a skimmer.

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Yep hydroids. I can actually see the image and videos now.. There's many types and it's hard to find the exact species when looking for an id which is why I think some people have bad experiences with them and some don't. I've never had any real problem with them and I think it's neat to see their life cycle in your tank.. They're basically like little jellyfish..

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thanks. I hope they're not going to be destructive. Absolutely curious to see how these develop; and where they came from in the first place! Nothing new has been added since my Green Chromis' 3 weeks ago

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