They're tiny little white ones with snail-looking shells. Francisco, I don't think they are as big as the ones in your link and the shell isn't shaped the same. I'll try to get some pictures to post, but they are really tiny.
One thing that's different in the past month or two is that my emerald crabs decided out of the blue that they hated other emerald crabs and killed each other. I haven't replaced them. Maybe I should. I'll try feeding them less as well - I've traveled a lot lately and they may have been overfed while I was gone.
Thanks for the offer Terry. They're easy enough to pull off the glass with a net lined with a coffee filter - just a nuisance that keep multiplying.