I.D. Please - Black slug like thing

[Smokey1]

Located on the right side of the photo. Jet black with a white dash in the middle of it's body.
It is approximately the size of a quarter.
Usually it is hidden in the rock, but I've seen it on top of one of my snails backs.
Is this a harmless grazer? Or should I be concerned?

I appreciate any feedback. Thanks

 

[tazdevil]

Looks like a limpet. Considered a good thing.

 

[Smokey1]

Do all limpets have a shell? This thing does not appear to have any sort of shell.

Thanks

 

[Smokey1]

I just took this pic, maybe it is better.
The body is an elliptical shape and it has a skirt
around it's body that is translucent, although
this is hard to make out in the photo.
The white marking that I usually see on it's back has disappeared.
The creature is completely black in color. The brown spots that appear
to be on him are on the glass. I haven't scrubbed the inside in a few weeks.

Is this typical of a limpet?

Thank you for your response

 

[Chucker]

Looks like a Scutus to me. You should be able to dig up info on previous threads on them with the search feature. You can also get a lot more at www.seaslugforum.net since people regularly mistake them for nudibranchs.

 

[Smokey1]

Yup, definitely a Scutus; Elephant Slug, Shield Slug, Ducksbill Limpet . I found a lot of good info on it. Thanks for all your help.