The nucleogenic cloud being was a nebula-like lifeform native to the Delta Quadrant. The lifeform measured seven AUs in diameter and was composed of hydrogen, helium, and hydroxyl radicals. The being used multi-polar charges for defense.
While looking for omicron particles on stardate 48546.2, in 2371, the USS Voyager accidentally harmed a member of this species by entering its body, not knowing it was a living entity. The crew of the Voyager performed a suture with nucleonic beams to assist the being in healing itself. (VOY: "The Cloud")