Mammillaria pectinifera

I have not watered my Mammillaria pectinifera since 20 th October. I kept it in a cool room (about 10 degrees) since beginning of November with my other mammillarias. All these are still without any apparent damage or disease. Only the spherical body of my M.pectinifera has changed. It seems to shrink into itself. Is the location wrong? Or should I give it a little water? I would be grateful for your advice. [list=1][*][img][/img]

Hi,
M. pectinifera does shrink a bit over winter, I have found. I keep mine at about the same temperature, but am always very cautious about watering until March.
However, it probably depends on how much shrinkage there is. If you really think it is too much shrinkage, and if your compost is very well drained ( as M. pectinifera likes) and you can perhaps give it some more warmth for just a few days after wards, then perhaps a very light watering or maybe just a spray shouldn't do too much damage, and you might see it bulk up a bit.
I don't find this plant an easy one myself, but having seen it grow in habitat, where it grows in small pockets of humus trapped in limestone rocks, it ought to be able to survive the kind of conditions you describe OK.
I think this is a good subject for some more views though, so don't be too hasty until others have had a chance to comment.