Black slug in tank ??
 

I was looking at my tank w a flashlight last night when i noticed a medium snail sized all black "slug" with two medium length feelers coming from his mouth area. He had no hard shell, thats why i call him a "slug". If anyone could help identify this guy that would b great, i tried taking a pic but it didnt turn out so well. He was no more than an inch in length.

slug
 

i have had one of those as well 'but mine had a thin tiny shell the same colour on its back,that wasn't tat noticeable.possibly a paper shell snail(harmless-sometimes their shell is inside the body) or a black limpet(eats coral)

look up stomatella. I believe thats how its spelled