Please ID this monster

[snail_chen]

I noticed this weird earthworm like thing recently. It hides in the caves and only and always come out when the light is off. Its mouth is surrounded with short red tentacles and the many rings on the body suggests it may be a annelid. Also there is a large mantle like lobe (below the worm as seen in the picture) in the same cave, which retracts when exposed to light. I don't know whether they are just different parts of the same thing or two different things.

Anyway, anybody can ID it for me? Is it a harmful creature? Well, even yes, I don't see how I can kill it.

 

[Bluemon]

peanut worm?

 

[GerritM]

Yes, a peanut worm --> probably Phascolosoma nigrescens (Distribution: Circum-equitorial).

Absolutly harmless and very good for your tank.

 

[BEASTIEPENDENT]

Yes, Gerrit's right, Leslie ID'd that one for me once. Strange looking, interesting creature. Perfectly harmless detritus feeder.

 

[snail_chen]

Thanks for everybody's response. I am glad to hear that it is harmless although it looks ugly.

One more question, is the big lobe like thing below it also part of its body or a separate creature? It can eject water when disturbed.

 

[CarbonMantis]

Most likely a separate organism, I'd think. If it ejects water it might be a tunicate, or "Sea Squirt" as they're often called.