Ok so i got home today after having my tortoise inside all day (because i had to go somewere, he is usually outside all day and he has a dark line on his shell which feels wet. He is always soaking in his water bowl and i dont know if i should be worried or not, he has had a little mark like it for his whole life (6 months) but it just grew today. He is a baby mojave desert tortoise. i live in southern nevada (las vegas) and im really scared! his shell seems to be softish but it is all around his shell, even the healthy part. What sould i do? Picture