The Marmosans were a race native to the Alpha Quadrant, outside of Federation space. They were one of the first Alpha Quadrant races to fall to the Dominion following the beginning of the Dominion War.
The Marmosans claimed the planet Bleak Prime, and established a mining facility on the planet to exploit its considerable resources. With the commencement of the war, the Dominion also took over this world, although the Marmosans were allowed to continue administrating the mining consortium, under Vorta supervision.
The Marmosans have three genders: male, female, and lherical. The lherical tend to serve as Objective Witnesses, or judicial executives. (DS9 short story: "Change of Heart")