Found this in LR.

[tombraider23]

We purchased live rock from someone tearing down their tank this weekend. Hubby was arranging the rock and this was hiding somewhere in the rock. What is it? If it's bad do we need to do anything to the rock/tank? It's 75 gallons and only been up for 1.5 weeks.

Thank you!


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[54seaweed]

nice score it's a feather duster there safe

 

[tombraider23]

It was a very dead feather duster! :-(


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[PB_Smith]

are you sure, they will often drop their "feathers" when stressed and hide in the tube until they grow back.
so if it dropped it's feathers that doesn't necessarily mean it's dead.
the tube is sand and mucus that the worm secretes.