The top pictures shows the seed pods of Mammillaria/Mammilloydia candida.
The next pictures shows that of M. pennispinosa. The seeds of this species are very distinctive. they have a large corky attachment called the strophiole. It is said that this allows ants in carrying it easily and hence aids in germination. Just visible in the same picture are the fruits of M. mathildae and M. jaliscana.
The third picture shows the fruit of M. plumosa (bottom), M. bocasana (middle) and M. bocasana ssp.eschausieri.