Weird chambers under substrate

[POLARBEAR0871]

I just noticed these weird "chambers" under my substrate I do have mytis shrimp and I also have a pistol shrimp somewhere in my tank...

 

[POLARBEAR0871]

I can't show any more pictures because they exceed the quota but I'll keep trying... The others aren't a tube the other two I can see are about a 1/4 of an inch tall and about a 1/2 inch long. It's sort of like an underground cave but in my substrate any one know what it is?

 

[Dav3]

Caused by worms. Nothing to worry about.

 

[POLARBEAR0871]

Ok thanks for the help I was just super curious