Is this a sea slug or something?

[rattslik]

I got heaps of new live rock yesterday thought nothing about it. Theno I turned on the lights like I normally do and bam this weird sea slug looking thing is in the back of the tank. From what I can see it doesn't look like a bristleworm but I could be wrong

 

[ahiggins]

Where did you get your rock from?

 

[rattslik]

W

Where did you get your rock from?

Well I'm in Australia so I'm guessing my local fish shop has got it from here

 

[ahiggins]

Oh wow
I’ve seen a handful of slugs but none like that, that’s why I asked

 

[scchase]

Sea cucumber

 

[Phycodurus]

the symmetry reminds me of a sea cucumber.

 

[Phycodurus]

possible match although yours looks much paler: greenfish sea cucumber (Stichopus chloronotus). sea cucumbers need well-established sand beds to thrive.

(https://reefguide.org/stichopuschloronotus.html)