Species 8472 are a race of exceedingly powerful beings that exist in the Star Trek universe. Originating from outside the Milky Way galaxy, they reside in a region known as "fluidic space", an expanse of organic liquid where they are the dominant (and perhaps only) life-forms. Their true name, if they have one, is unknown; the designation "Species 8472" was given to them by the Borg, a collective pseudo-race of cybernetically augmented beings.
Species 8472 are tripedal, around three 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. They are known to have as many as five genders. The species' immune system is able to destroy anything which penetrates their bodily systems: chemical, biological, or technological. They are impervious to normal Borg assimilation methods. Their immune system can even be used as a means of attack. If cornered, they attack with their claws rather than with any other type of weapon, allowing their cells to come into contact with a victim's where they will infect every system and consume it from the inside out. In addition, if threatened, Species 8472 are able to commit suicide by releasing a cellular toxin into their bloodstreams. They emit a biogenic field around their bodies; this field renders them nearly invisible to sensors, making it impossible to pinpoint their exact location. This field also interferes with normal transporters. Exactly how this biogenic field is produced is unknown.
Physiologically, Species 8472 are non-humanoid. They are 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.
Although capable of auditory communication with other species, communication via telepathy is the standard between their species' own members. With their dense musculature and increased height, Species 8472 possess great flexibility and can move much faster than any known humanoid beings. They are able to penetrate force fields and rip through bulkheads with apparent ease.
They have very little soft tissue, and much of their skeleton is exposed, particularly around their necks. They do appear to have nostrils, suggesting a sense of smell; however, they possess no ears or mouth and have distinctive cross-shaped pupils. They appear purple to green depending on the lighting. It is not known if Species 8472 is the only species to have evolved in fluidic space, if they share it with any as-yet unknown species, or if they exterminated any such others as they attempted to do in normal space.
Nearly nothing is known about Species 8472's culture due to the species' xenophobic nature. In all their contacts with the Milky Way, they have been known to be aggressive and single-minded in their aims to destroy all other forms of life. It is possible that they believe all races are hostile and need to be destroyed.
During their first invasion into the galaxy, a common telepathic command that would be sent from their minds would be "The weak will perish". This perhaps suggests that the race believes in a survival of the fittest policy and do not tolerate 'weaker' species. However, they also believed that the intrusion into their realm by the Borg was a threat to their 'genetic integrity' but as to what this means is unknown. It is perhaps possible that having not encountered another species before, that Species 8472 were simply responding to the threat of invasion as the Borg were the race that had first attacked them.
Species 8472's central authority and leadership are not known to the powers of normal galactic space, nor is it known exactly how centralized their organization is or how widespread their telepathic connection to each other is.
Species 8472 utilize organic technology comprised of the same material they themselves are made of. This makes their vessels unusually resilient against any attacks. They are also capable of shape-shifting using a form of genetic manipulation, and can switch between different forms at will.
Species 8472 travel through space in bizarre organic vessels comprised of the same biological tissues they themselves are made from. These bioships are relatively small, about half the size of an Intrepid-class Starfleet ship, but are extremely powerful. They generate biogenic energy fields that interfere with most other forms of technology, preventing sensors from penetrating their surfaces, prohibiting transporter locks and making them impervious to most weaponry. Any damage that is sustained quickly regenerates and whatever matter breaches the cell membranes is immediately destroyed.
Bioships are not only impervious to attack but are each a weapon of mass destruction. The biogenic energy which they generate can be projected as a devastating arc of bioplasma capable of destroying any ship in only one or two shots. Even the Borg's massive cube ships, well-known for their overwhelming power, stand little chance against a Species 8472 bioship. Not only can a single bioship lay waste to an entire fleet of starships, but several o them in a group are capable of generating a bioplasmic blast of planet-busting proportions. During their war with the Borg, Species 8472 bioships combined their energy to destroy numerous Borg-occupied worlds.
- In the non-canon MMORPG Star Trek Online, Species 8472's true name is revealed to be "Undine". The name Undine is taken from the ancient term for a water elemental in Earth mythology, an appropriate label considering that Species 8472 originates from a fluidic realm.