In the mirror universe, the Penemu were a highly advanced race that were conquered by the Klingon Empire.

In the late-2240s the Penemu were forced to develop a highly destructive weapon for the Klingons. This weapon was capable of destroying a class M planet and eradicating its inhabitants. This weapon was tested on Donatu V and was partially successful. (Mirror Universe short story: "Ill Winds")

It is unknown if the Penemu existed in the primary universe.
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