White lines on/under shell of Russian tortoise

[WalnutWordsworth]

My russian tortoise has had the white squiggles that seem to be under the shell for some time. He shows no signs of being ill, doesn't smell bad so I don't suspect fungus, and loves his food and bath time. Please have a look and tell me if it's a nutritional deficiency or if he needs more UVA/UVB.

 

[wellington]

It's nothing to worry about. Not sure why some tortoises get them but it's very common.

 

[Tom]

Normal and not harmful. Nobody seems to know what it is.