parasite or harmless nematode?

[cellodaisy]

Did yours have the distinct head section?

yes they did.

That makes me feel a lot better. Thanks!

 

[Star_Rider]

internal parasites need a host... so you can pretty much rule them out.

ahh leeches.. they swim and there are many species fortunately they have distinctive mouth ends. remember that leeches do have a juvenile stage...thin , thread like but generally will take the normal leech shape when contracted
and at this size probably a good source of protein for fish