Snail or.... ID please?

[TravelinLight]

Just found this on a piece of rock in my sump. Never have seen it before- good or bad?

<a href="http://s943.photobucket.com/user/mfeldman21/media/Mobile%20Uploads/image_zpsd43ef895.jpg.html" target="_blank"><img src="http://i943.photobucket.com/albums/ad273/mfeldman21/Mobile%20Uploads/image_zpsd43ef895.jpg" border="0" alt=" photo image_zpsd43ef895.jpg"/></a>

 

[Deinonych]

Wrong forum...recommend posting this in the Reef Discussion section.