Strange shape in substrate

[Neleono]

So I just walked into the room where I house my aquarium backed pets and I get to my crab tank and I’m there little hollowed out half log that is in the tank I see it’s filled up a bit with sand with somthing dark in the middle. Upon closer inspection I see that the dark thing it an almost perfect circle of eco earth. Does anyone know what this could be? Is it somthing I need to be cautious about or is it just a strange thing my crabs have done. I know that my substrate isn’t good, I’ve been meaning to replace it but one of my crabs has been what I think to be molting. Also, I made my substrate in a way that it is half ee and half sand that are separated so I don’t know how they could have moved so much ee into the middle. Thanks for the help, will be posting pics in the comments soon.

[Neleono]

Pics:



First picture is the ee circle from top view when log is removed.

Second and third pictures are a front facing view when log is where it normally is.

Forth picture is a picture of the half and half substrate idea I described before.


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[Neleono]

This guy has been sitting on it ever since I made this post if this helps confirm any theories.


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[wodesorel]

I know they say that perfect shapes don't occur in nature, but sometimes it really is just a coincidence. My guess would be that it's a clump of cocofiber the crabs picked apart, or possibly a pile of dry and crumbled poop.

[Neleono]

Ok thanks! I was worried of something much more like a nest or something (idk how crab children work)


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