Strange ring in the sand

[Rmorrison23]

Anybody have a clue what could have done this?
My friend woke up to this in his 24G nano. Only has 1 fish, few snails, and a few corals. His tank is only around 2-3 months in.
Thanks

 

[Steven Garland]

Maybe some type of invert hole that came in on somethibg ? Maybe spaghetti worm hole,although I have never seen them do that.

Is it all dry rock that was used ?

 

[Rmorrison23]

Maybe some type of invert hole that came in on somethibg ? Maybe spaghetti worm hole,although I have never seen them do that.

Is it all dry rock that was used ?

Dry rock, live sand

 

[vetteguy53081]

try to lift gently and see if there is a tube or foot attached to structure.

 

[Reefer Reboot]

Don't know for sure but it does look a lot like sand collars that are left by moon snails. Maybe he has a snail that does something similar.

 

[BeltedCoyote]

j/k (couldn’t resist)

I’d see what’s under it

 

[RobB'z Reef]

Crop circles!

 

[G Santana]

Crop circles!

Lol my first thought