What is this white eel / worm thing?

[Just John]

I wish I could get a better picture, but it's in a back corner where a scraper doesn't fit. It's about 1.5" long, swims like an eel, appears to be flat, looks like it is wider on one end or has a larger finned area like the the end of an eel, Jagged on the wider end, but has no head. It will have come in with some gulf live rock I got a couple of months ago.

 

[Sharkbait19]

Looks like a lancelet. I don’t think they are harmful at all, but definitely rare.

 

[Just John]

Looks like a lancelet. I don’t think they are harmful at all, but definitely rare.

You are right! I looked up some photos and that definitely looks like it.