It could be M. lloydii

You could be right cochemiea.I googled M.lloydii and some of the pictures look just right my plant.But there are some others quite different with more sparse areoles.Does anybody knows if M.lloydii has 2 forms??

I would have said it doesn't look anything like M. lloydii, which normally has no central spines. Or no radials if you think the spines look like centrals :)

Do you have a link to some that you think look like your's? They may be incorrectly labelled. I found this which I'm 99% sure is wrongly labelled.

Shrubs ur link is actually one of those i found matching my plant.Here's one more that seems to be from a reliable source:

Here is a link that might be useful: M.lloydii??

Yes, I see the resemblance. But if you look closely you will see that the mammillarias.net picture has just the four spines, while your's has four(-ish) plus lots of little white ones.

I think you may have a Mammillaria sempervivi, which has these half-hearted white radials but usually loses them when it gets older.

You're right about the spines shrubs.Haven't noticed that detail...Still i'm not convinced it's a sempervivi.I found very few pics matching my plant and those were on Webshots probably mislabeled).Also i noticed that young M.sempervivi plants have a more flattened body than my plant was when i bought it.

Who knows with all these mammillarias maybe its a hybrid..Now u know why i stopped buying cactus plants and only sow named variety seeds..

Thanx for helping everybody!

Hello arcana,
Shrubs n bulbs is correct that it is not lloydii, because of the many persistant radials; but for the same reason it does not conform very well to sempervivi either.
Good luck with your seeds, as you say, named varieties offer fewer problems identifying the plant but also it is true that there is no guarantee that the name is correct.
If I have any further ideas about your Mammillaria I will contact you.