snail id

[twon8]

i have a lot of these in my tank, most only seen at night, but here is a shell. They have black "trunks", sort of like a conch, but the biggest i have seen is about 1/2 inch. Any ideas as to type. I am pretty confident that they are not harmful but I would like to be certain.http://i3.photobucket.com/albums/y78/twon8/Corals/snailshell.jpg

[bertoni]

A shot of the whole shell might help. Also, a picture of the opening of the shell, with the animal retracted, might be useful.

[twon8]

whole shell
any ideas on an id?
http://i3.photobucket.com/albums/y78/twon8/Corals/snail.jpg

[LeslieH]

Looks like a Nassarius to me. According to Ron's column http://reefkeeping.com/issues/2005-11/rs/index.php
this is one of the few whelks that are okay in a tank, being a scavenger rather than a predator.