Some kind of Slug?

[MikeLee]

Hello all,
I’ve bought some live rocks locally and now I’m getting all these hitchhikers.
Amphipods, isopods, sand worms, and now this.
I couldn’t find it on the web.
It’s about 2~3mm when extended.
Any ideas?
Thanks!

 

[reef lover]

Could be a peanut worm

 

[MikeLee]

Maybe baby peanut worm?
It had no antenna nor legs.

 

[MikeLee]

Now that I think about it, it is more like 4~5mm when extended.