OhhFungus is usually found on plastrons . This baby’s shell is beautiful! I see nothing wrong with it
It happened recentlyIs this the case since you got him or this happened recently? Is he/she eating well? Is it active? How old is he? I think he's not even a year old it might be the remains of the egg it hatched from.
ThnxI see nothing to worry about. The white lines in between the scutes is new growth coming in.