View Full Version : Blue-green worm with white zig-zag marking ID help please

05/07/2017, 08:22 PM


So last night I found this striking blue-green worm (I think it's a worm) in my tank. He's about 1/4" diameter with a round body and a flat head that has the prominent zig-zag white lines on it.

He stretched out from a rock crevice onto the sand about 6" or so, grabbed and swallowed a blue leg hermit crab in shell and retreated into the crevice. He spit him out a minute later. Never seen him before and can't find him again today.

He's actually quite a beautiful specimen but seeing him try to eat a crab was off-putting. I'm wondering what it is and if I should be worried enough to try to remove him. I have a mixed reef.


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05/07/2017, 08:32 PM
How long has it been since you've added something out could've hitch hiked in on?

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05/07/2017, 09:12 PM
I haven't added any rock or coral on rock in a long time, at least a year or two. I've recently (within the past month) added a clean up crew like small snails and crabs, as well as an anemone, small plate coral, arrow crab. I wouldn't be surprised if he's been in my tank for a long time hidden, I have a lot of rock work and crevices.

I just came across a WetWebMedia archive FAQ page where Bob Fenner ID'd something that looked similar as a Nemertean worm. There were disparate discussions of it being a carnivore that may go after clams and invertebrates, but also that it might be safe in a reef tank.

I'm hoping someone here might have some more experience and info.

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05/07/2017, 11:30 PM
Yes, it's a nemertean. You can probably search Notospermus on this forum and get some good info. They are predatory.

05/08/2017, 01:00 AM
Thanks, I did find some additional useful discussions with that name. Sounds like he will be a problem. Finding and removing him won't be easy though.

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Shawn O
05/11/2017, 12:41 PM
Tie a small crab to a stake and leave him out overnight. :)

05/11/2017, 05:39 PM
Poor sacrificial crab :)

I'm planning a tank upgrade soon so I'll try to find and remove him then, but even with looking closely at every rock I'm not confident I'll find him.

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