black nudibranch

[fender316]

i seem to have spotted some sort of black slug in my tank im wondering how safe he is.  he's in a hard to see crevice so my pic isnt that helpfull.  all i can see is black with 2 white dots, the black has a little blue tint to it under the flashlight.

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[Julie]

It's really hard to see what exactly it is.  Any more pics?