Please help!! Found jet black slug with white spot on his back, good or bad?!

[Smokin'Reefer]

I will upload an image soon, the rocks / sand in my Nano tank are almost 4 years old, recently found a black slug about 2cm long 1cm wide with distinctive white spot on his back, other than that he is jet black with long antenna things, will he nuke my (10Gallon)tank when he dies? 

[king aiptasia]

30 minutes ago, Smokin'Reefer said:

I will upload an image soon, the rocks / sand in my Nano tank are almost 4 years old, recently found a black slug about 2cm long 1cm wide with distinctive white spot on his back, other than that he is jet black with long antenna things, will he nuke my (10Gallon)tank when he dies? 

sure he is not a limpet?

[NoOneLikesADryTang]

From your description, it sort of sounds like an elephant slug. 

[mcarroll]

One of the most beautiful reef creatures IMO.   Always a blast to see when they come out of hiding.  

 

Nothing else like it.

[Harrisonbored]

Could be a black Stomatella.  When mine were smaller they had white shell backs, but as they've aged (or possibly because of diet) they've turned grey, tan and even light yellow.

 

 

Sorry for bad photos but they're always in tough spots to shoot.