In 2376, the crew of the USS Equinox encountered a series of nucleogenic lifeforms which originated from an extradimensional realm. Capable of gaining access to the normal spacetime continuum via the generation of interspatial fissures, they were only able to survive outside their own realm for short periods of time before they were forced to retreat back through the fissure. The Equinox crew was introduced to these lifeforms by the Ankari, a species native to the Delta Quadrant, who regarded the lifeforms as "spirits of good fortune." Deciding to assist the Equinox crew, whose ship was badly damaged and running low on essential supplies, they summoned the spirits in order to bless the crew's journey home. Scanning the lifeforms, the Equinox crew discovered that they were emitting high levels of antimatter, and subsequently constructed a multiphasic chamber to confine the lifeforms for the purpose of study. During the course of their examination, however, the Equinox crew found they were unable to release the lifeform from the chamber, resulting in the lifeform's death. Examining the remains, the crew discovered that they could be converted into a source of fuel with which to augment their warp drive. The crew performed this action by modifying the multiphasic chamber with a polaron grid and a submolecular resequencer to convert the remains into a crystalline compound. They then biochemically altered the compound to extract the base proteins, thereby gaining access to the nucleogenic energy stored within. Instituting the necessary warp core modifications, the Equinox successfully traveled over ten thousand light years in less than two weeks. However, since the energy extracted from a single lifeform was only useful in increasing their warp factor by 0.3 percent for a single month, the crew began to systematically murder more of the lifeforms and perform the procedure repeatedly, presenting them with the possibility of returning to the Alpha Quadrant in mere months.
The lifeforms, however, were not incapable of defending themselves, and began attacking the Equinox. Although the Equinox's shields were effective in preventing the lifeforms from opening their fissures within the habitable volume of the ship, the lifeforms were able to systematically drain their shields by opening the fissures in close proximity to the shield perimeter, attacking and killing Equinox crewmembers by inducing a fatal thermolytic reaction through physical contact upon penetration of the shields. The Equinox was weathering one of these retaliatory attacks when they were discovered by the crew of the USS Voyager, another Starfleet vessel which had been stranded in the Delta Quadrant. Using their own shields to reinforce the Equinox's, the Voyager crew assisted in defending against the attacks. Personnel from both vessels cooperatively developed an auto-initiating security grid which would trap the lifeforms behind a multiphasic force field whenever one appeared. After the Voyager crew uncovered the illegal actions of Equinox crew, however, the Equinox crew stole Voyager's field generator and withdrew, planning to continue their experiments. (VOY: "Equinox")
Meanwhile, the lifeforms continued to besiege Voyager. As the crew was unable to capture the Equinox or develop a translation matrix for the lifeforms' language, Commander Chakotay suggested that they seek out the Ankari as intermediaries. Through them, Captain Janeway promised the lifeforms that she would allow them to destroy the Equinox if they halted their attacks. When Voyager finally intercepted the Equinox, Rudolph Ransom, the ship's captain, agreed to surrender to Janeway, having experienced a change of heart. In response, Ransom's first officer, Lieutenant Maxwell Burke, staged a mutiny, taking command and attempting to destroy Voyager. Ransom was able to gain access to transporter control and beam the majority of the surviving crewmembers to Voyager. Upon the disengagement of the Equinox's shields, the lifeforms gained access, killing the remaining crewmembers and destroying the ship by attacking the warp core. Upon the destruction of the Equinox, the lifeforms retreated back to their native realm. (VOY: "Equinox, Part II")
- Creating the appearance of the nucleogenic lifeforms involved the work of many visual effects artists. Stated Visual Effects Supervisor Ronald B. Moore, "The creature ultimately was designed at Pacific Ocean Post. All of the [CG] vendors did drawings. P.O.P., Foundation Imaging, Digital Muse and Santa Barbara Studios all put in some drawings. [Supervising Producer] Peter Lauritson and I went over it with [Executive Producers] Rick Berman and Brannon Braga. They picked the one that they liked, and we had that modified a little bit to satisfy everybody that we could." Director David Livingston also viewed some of the illustrations. He remarked, "The drawings that Peter Lauritson showed me of the creature were wonderful. It starts off as being this beautiful, butterfly kind of creature, and turns into this horrible, murderous thing, because we do bad things to it. Peter is taking the creature to Santa Barbara Studios [....] I think they are going top cabin on this one, to really make it wonderful." Work on visualizing the lifeforms was completed at Santa Barbara Studios. (Cinefantastique, Vol. 31, No. 11, p. 46)
- The nucleogenic lifeforms resemble the Etherians from the game Star Trek: Voyager - Elite Force, but do not seem to be related.