Nassarius incrassatus - the bump

[BubikolRamios]

this have a bump:
http://agrozoo.net/jsp/Galery_one_image....d50b5886e4

See attached group, only one with bump, what does that mean, if anything ?

EDIT: Ok , educated myself (-:, the bump is called Varix,
http://en.wikipedia.org/wiki/Varix_%28mollusc%29
and should be species specific ? Hence attached image more interesting. That is , mybe 'the others' did not have any resting stages jet ?