Fungal Infection ????

I bought this Coryphantha and a Mammalaria from an online nursery. Both developed these orange areas; one within days of arrival and the second after I repotted it. Is this a fungal infection? Am I responsible? None of my other cacti have this. Thanks.

If the on-line seller is one of the more respected cacti growers, he should be able to help with the ID of the cause if you contact them. At first glance it could be red spider mite, in which case, keep them separated for the time being until treated. Or another possibility is, if the seller has kept them in greenhouse conditions and you are keeping them indoors atm, as I can see others in the background, and probably near or on a window sill, the change in temperature could be the cause. The temperatures of late, especially at night, close to a window can be quite cold.