Does anyone know what these are

[MrMudkip]

They appear to be little circular shells on these rocks from my old system 7 yrs ago. They've been out of water for 7yrs and I am gonna bleach the rocks soon, but didnt know what they were.

 

[ThRoewer]

Those are tiny feather duster tubeworms. Generally beneficial.

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[Anemone]

Little fan worms. Common hitchhiker on live rock and in our systems. They usually have small red feather fans.

Kevin