The Nucleogenic Lifeforms are extradimensional species discovered in the Milky Way's Delta Quadrant. Their molecular structure naturally stores enormous quantities of nucleogenic energy, and they are known to emit large quantities of antimatter. They are only able to survive for a few seconds in our realm. Physically, the creatures resemble flying sirens, with an elongated body with four-fingered humanoid arms and no legs. They are mostly dark green, with a yellow ventral surface; and have noseless faces with a pair of black eyes and a toothed mouth.

Although not usually hostile, they have the ability to kill humanoids almost instantly by dehydrating every cell in their bodies. A species called Ankari has created technology that allows them to summon the lifeforms into our normal realm for a few seconds. They use this on spiritual practices as they regard the nuclegonic lifeforms as spirits of good fortune. The term "nucleogenic" strongly implies that the lifeforms run on a nuclear rather than chemical metabolism, and might explain why their bodies can generate so much power, enough to propel a starship more than 10,000 light years in less than two weeks.

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