Species 8472 is the Borg designation for a non-humanoid species whose actual name is unknown. 8472 was first encountered by the Federation starship USS Voyager in the Delta Quadrant in 2373. The species originates from a dimension called fluidic space, accessible by quantum singularities. (VOY: "Scorpion, Part I", "Scorpion, Part II"). They are believed by the Borg to be the ultimate form of biological evolution.
In their search for further species worthy of assimilation, the Borg first encountered Species 8472 after they found a way to enter Fluidic Space in the 2370s. However, Species 8472 turned out to be immune to the Borg's assimilation attempts and the invasion of their realm provoked a war, which quickly evolved into the first real threat the Borg had faced in thousands of years. With their superior technology, Species 8472 was able to annihilate hundreds of Borg planets, thousands of Borg ships and billions of Borg drones. Species 8472 was forced to retreat when the crew of the USS Voyager armed warheads with modified nanoprobes, capable of destroying their bioships. (VOY: "Scorpion, Part I", "Scorpion, Part II", "Prey")
When they retreated to fluidic space, one member of Species 8472 was left behind and was relentlessly hunted by a group of Hirogen hunters for several months. This individual was later rescued by the USS Voyager, and Captain Kathryn Janeway intended to return it to Fluidic Space. Seven of Nine, however, refused to open a rift to Species 8472's realm. It later proved to be irrelevant because in a struggle with the Hirogen, Seven of Nine transported the individual to the Hirogen vessels, which then broke off their attack. (VOY: "Prey")
Concerned about the threat posed by Humanity with its modified nanoprobe-warheads, Species 8472 created a simulation of Starfleet Academy on Earth inside a Species 8472 Biosphere in the Delta Quadrant as a training ground for a potential infiltration of the Federation. However, the plan was uncovered and eventually stopped by the crew of the USS Voyager who convinced Species 8472 that the Federation had no hostile intention toward them by giving them their modified nanoprobe warheads in hope that Species 8472 could adapt their vessels. (VOY: "In the Flesh")
Apparently, Species 8472 continue to make non-hostile patrols in the Milky Way galaxy, possibly against the Borg, and are said to have teamed up with the Borg liberated from "Unimatrix Zero" (ref. Unimatrix Zero, Part II).
Species 8472 is tripedal, around 3 meters tall, extremely muscular, and biologically unique. Their DNA is arranged in a triple helix formation, and is the most densely coded DNA ever encountered by Starfleet. The Species' immune system is able to destroy anything which penetrates their body systems; chemical, biological, or technological. They are impervious to normal Borg assimilation methods. Their immunes system can even be used as a means of attack. If Species 8472's cells come into contact with a victim, they will infect every system and consume it from the inside out. In addition, if threatened, Speicies 8472 are able to commit suicide by releasing a celluar toxin into thier bloodstream.
Physiologially, Species 8472 is non-humaniod. They are tripedal and able to withstand the vacuum of space. It is probable that in fluidic space they are able to swim through the organic matter similar to their ships, which share their unique physiology. They communicate exclusively via telepathy. Kes was able to make contact with Species 8472 while they were in conflict with the Borg; they vowed 'the weak will perish'. Tehy also generate a biogenic field, which makes them difficult to find with conventional sensors. With their dense musculature and increased height, Species 8472 posess great lithe and can move much faster than either humanoids or Borg. They are able to penetrate forcefields and rip through bulkheads with apparent ease. They have very little soft tissue, and much of their skeleton is exposed, especially around their necks. Species 8472 does appear to have nostrils, suggesting a sense of smell; however, they posess no ears or mouth and have distinctive cross-shaped pupils. They appear purple to green depending on the lighting and have 5 different sexes. It is not known if Species 8472 is the only Species to have evolved in fluid space of ir they exterminated they others as they are attempting to do with normal space.
In conjunction with the Borg, The Doctor developed modified nanaprobes which were able to effectively combat Species 8472 and thier bio-ships. The nanaprobes could be modified to either kill or sedate they creatures.(VOY: "Scorpion, Part I", VOY: "Scorpion, Part II", VOY: "In the Flesh", VOY: "Someone to Watch Over Me". Star Trek: The Magazine Issue 5)
The Bioships used by Species 8472 are very advanced and share their unique geneitc makeup. They are living organic vessels capable of warp speed, and are very heavily armed and shielded. Inside, the walls and floor appear to be flesh, spider web like material is used in place of an EPS system. The structural supports are made of bone. The ship's computer is similar to a nervous system and uses neuropeptides. The ships are native to Fluidic Space and are able to function as well in the organic matter of fluid space as their are in the vacuum of normal space. They are also equipped to decect the pressure wave created when a vessel crosses into fuildic space from normal space.
A bioship carries only one crew member, who acts as the pilot. Its hull is resistant to conventional weaponry, including Borg assimilation, and also reflects sensor scans and tractor beams. The bioships are armed with energy beam weapons, the beam appears less coherent than either Starfleet or Borg weapons, but is able to inflict greater damage. Voyager was knocked off course by a beam that just missed it. Several bioships can combine their firepower to destroy entire planets.
It is unknown whether the ships evolved naturally or if they were engineered to fit their task by Species 8472.