no clue what.this is

[holtzbrandon]

this showed up in mytank randomly one day. several of them

on the substrate only . look like brown discs with rings

 

[Fin]

Do you have any dead snails in the tank. That sort of looks like it might be the trap door off of a snail shell (for lack of a scientific name for it). Can't really tell how large it is.

 

[luxauterna]

I agree with Fin