what type of slug is this

[joe&rae]

I recently found a sea slug in my fish tank I dont have any idea where it came from can some one please help me find out what type of sea slug this. sorry the picture is not all that good my camera died and i could only get one good one

 

[roka64]

Moved to the ID section.
Is it a slug or a snail? It looks like it has a shell.

 

[joe&rae]

it looks like it but no it is not a shell it looks like one but iit moves just like its body!!

 

[ThrowedToad]

Does it look something like this?
http://i119.photobucket.com/albums/o154/throwedtoad/S7300645.jpg

 

[joe&rae]

yes but a lot smaller shell

 

[joe&rae]

here is a kicker i had only seen 2 one pinkish and one black!! now there are about 15 20 that i can see and most of them are on the front glass but slightly below the sand!!!!!