Klaestron were humanoid, with distinct streak-like protrusions on the side of their head above their ears. Their outer ears consists only of a hole in their head.
The Klaestron Civil War took place in the mid 24th century. Although they have an unilateral extradition treaty with the Federation, the Klaestron are allies with the Cardassians. Treason and murder are punishable by death among the Klaestron. (DS9: "Dax")
Around 2371, the Klaestrons developed a new burn treatment technology. That year, Doctor Julian Bashir visited Klaestron IV to review the new technology noting that it "has to be seen to be believed." (DS9: "Second Skin")