Yes they do. I just got an order in today from this site, some blue and green striped shrooms and I found a big one and a small one on my blues and a big one on the greens.
I did some reseach on them and it said to inject white viniger (full strength) into the mouth, and it should kill it. I also read you can use B-Ionic Alk and that will kill it.
There is a product called Joe's Juice also. I do not have any, will have to order it if the viniger or B-Ionic does not work. Scares me to know they are in my tank. Just saw them tonight.
I have another order from SWF coming in tomorrow, so I plan on taking the shrooms out and trying the viniger and or B-Ionic., when I acclimate my order.
Anyone out there have any other ideas to get rid of them?