Strange things at night

[ISpeakForTheSeas]

Could they become a problem in my tank? I know they are good CUC, but I can’t believe I have at least 3. So should I leave them be?

I doubt they'll be an issue (so I'd leave them be as long as you think you/your tank can keep them proper fed), but if you start finding a lot more or if they start causing issues, I'd be interested to know.

 

[Sophie"s mom]

I doubt they'll be an issue (so I'd leave them be as long as you think you/your tank can keep them proper fed), but if you start finding a lot more or if they start causing issues, I'd be interested to know.

I will certainly keep you updated! Thank you

 

[Sophie"s mom]

I doubt they'll be an issue (so I'd leave them be as long as you think you/your tank can keep them proper fed), but if you start finding a lot more or if they start causing issues, I'd be interested to know.

Oh and as for proper feeding, I keep nori in my tank for miscellaneous creatures because thankfully I don’t have much visible algae.

 

[Huskereef]

Typed in tube worm with a long string and this thread pulled up,
Looking at the tank late at night. Thought I would share a picture of what I would describe as a tube worm with a long string/rope that can extend up to at least a foot. If startled it retracts very fast back into the live rock. The base of the worm is stationary. It uses the flow to move around. The end of the stringy rope has a V shape as if it uses it grab things. Very odd. Any idea?

 

[ISpeakForTheSeas]

Typed in tube worm with a long string and this thread pulled up,
Looking at the tank late at night. Thought I would share a picture of what I would describe as a tube worm with a long string/rope that can extend up to at least a foot. If startled it retracts very fast back into the live rock. The base of the worm is stationary. It uses the flow to move around. The end of the stringy rope has a V shape as if it uses it grab things. Very odd. Any idea?

Female Bonelliid Spoon Worm:

That's a female Bonelliid Spoon Worm/Echiuran - most spoon worms are harmless detritivores (good CUC), but a few (likely including yours) have a toxin (Bonellin) on their proboscis (the forked "mouth" mentioned above) and/or skin; these eat things like small pods that succumb to the toxin when crawling on/over the proboscis.

These would probably be fine to keep in the tank as long as you think your critters are smart enough not to touch the proboscis, but it may carry some risk (especially for smaller critters, and especially if your female has one or more males - which are tiny - living with it so that it could reproduce):

be aware that it is toxic (the toxin is called Bonellin, and I’m not sure about it’s effects on people), and please handle it with care and a good pair of gloves.

If you decide to keep it, I'd probably suggest running carbon and doing regular water changes to be safe.

Bonelliid spoon worms exhibit extreme sexual dimorphism - the females are large while the males are extremely tiny and often/always live literally inside the female. So, by seeing the worm's regular-sized proboscis extended, you can tell it's female (no idea if it has a male with it or not though).

Unfortunately no idea how harmful the toxin is - as a general rule, the physically greener the worm, the more toxic I would expect it to be, but I don't know how much of the toxin it would take to harm a small fish.