The Nassordin were an alien species native to the Delta Quadrant.
In 2374, the Nassordin were engaged in trade negotiations with the B'omar Sovereignty. (VOY: "The Raven")
This species was only mentioned in dialogue.
The species name "Nassordin" was devised by Bryan Fuller. He took inspiration for inventing the name from a book about angels which he owned. (Information from Larry Nemecek)