Nassarius Snails

[Baker]

So a couple months ago I decided to revitalize my 20g long frag tank. I had allowed this tank to completely go to **** and the detritus was so bad that the bottom was covered in about a 1/2". I sucked some out when I did a couple of water changes over a few weeks but it just kept coming. So, I went out and got about 20 nassarius snails. At first I didnt think they were going to do the job but in this last month with doing water changes and the persistant lil' buggers working hard I am down to a few small patches. This isnt why Im typing this up though. Today I noticed a tiny little snail on the glass in the shape of a nassarius snail. I thought they werent known to breed in captivity. Its definitely a nassarius. I dont have any other snails in there other than some trochus and this isnt in the shape of a trochu. Can anyone shed some light on this? They arent the mini ones either. They are the 1" snails.