I've got hundreds of these very small white snails in my tank.  They're about 1-1.5 mm wide by 2-3 mm long, bone white and, as you can see in the picture, have a very pointy shell.  I've read a few articles about parasitic pyramid snails and it has me wondering.  The pictures on the net of pyramid snails look just like what's in my tank.  The only strange thing is they are not attached/sucking on any host that I can see.  They come out only at night and scoot around everywhere; rocks, glass, substrate, my big red sponge, zooanthids... everything.  I've never seen one during the day... I've never seen one on any of my snails, corals or clam other then at night.

Mark, is this what the snails on your clam looked like?  Anyone else have these snails in your tank?  Really the only thing that has me wondering if they're pyramids is the body shape... by behavior I'd say they're algae/detrius grazers, but I don't know.  What do you think?

Jon,

It looks to me like they are Chestnut Nassarius snails.  It is hard to tell from the picture, but I wouldn't worry about them unless they are doing something harmful in your tank.

Jake,

Is that the Nassarius snail you're selling in your store?  I added some nassarius snails from your store about a month or so ago... the timing might not be a coincidence.  Perhaps my nassarius have bred?  I'm pretty sure the small snails spend the daylight hours in the sand bed.

I looked closer at them last night with a magnifying glass, they do have a foot like a nassarius (but appeared to have a mouth more like an asteria).  Much to small to see if there's a "trunk".

I noticed them about 5 days ago and they don't appear to have "hurt" anything.  Like I said before, the body shape had me wondering.  I doubt I could do anything to control the population anyway .

Jon,

I carry regular nassarius (which are black) and chestnut nassarius (which are a lighter color).  Depending on the collector I get one or the other.  For the last couple months I have been selling chestnuts.  It may be that they have bred in your tank (this is not uncommon).

Well the little buggers have about doubled in size now and I'm pretty sure they're nassarius.  The trunk is clearly visible and they're starting to color up like the adult chestnut's in my tank.

I wouldn't worry about it for a while.  I didn't mean to sound like it was the end of world or something.  If they do get outta hand, just get a brittle star or something like that.  They live in the dark.