Parasite in my tank?

[uncle al]

I see this worm like creature in my friends tank. It’s been hiding under a rock so I can’t good a good look, but any ideas what it might be? They definitely didn’t buy this creature so they aren’t sure how it showed up

 

[Jay Hemdal]

I see this worm like creature in my friends tank. It’s been hiding under a rock so I can’t good a good look, but any ideas what it might be? They definitely didn’t buy this creature so they aren’t sure how it showed up

View attachment 3095071

Tough to see in the picture, but the general rule is that something that lives free in a tank isn’t a parasite.
Jay