The Alcyones were a civilization that destroyed what was believed by the Federation to be the last Tarellian vessel, in 2356.

It was later discovered that the ship they destroyed was not the last plague ship, following the discovery of another such vessel near the star Beta Cassius in 2364. (TNG: "Haven") linked the Alcyones to the real star Alcyone (also known as Eta Tauri, and part of the Pleiades), which it claimed to be a B class giant 541 light years from Sol. It is currently believed to be closer to 400 light years away.
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