Monster vermetid, or alien invasion?

[W1ngz]

What is this? It looks like a giant vermetid snail, but the opening is close to 4mm wide and it's over 1cm tall.
For reference, I also have a few vermetid snails, and there's one in the foreground.

 

[Leslie Tabor]

They do get REALLY big!

 

[W1ngz]

They do get REALLY big!

In a week? It wasn't there 10 days ago.

 

[Leslie Tabor]

Ooh that I don't know. But I had a giant one once upon a time. They seem to just die off as the tank matures. You could always cover it with some reef putty/glue to be safe.

 

[vetteguy53081]

Either a spiral tube or Calcareous tube worm

 

[CoralReefer1019]

You will have to glue there holes shut

 

[NowGlazeIT]

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