Help worm in tank

[oconn21]

just found this crawling on a rock this morning tank has established about 9 months last new thing that went in was about 2 months ago and it was coral from WWC and I did dip. Is it something to worry about it now that I got it out?

 

[Goaway]

cant tell what it is out of water. place in a glass and try some pics, could be a peanut worm.
or a sea slug

 

[Sharkbait19]

Lancelet?

 

[oconn21]

Lancelet?

It looks like that but from what I’m seeing they don’t live long in tanks