Living starship of Species 8472, grown from organic matter and armed with a beam powerful enough to destroy a Borg cube.
Species 8472 bioships were organic vessels that were grown rather than built, sharing the genetic make-up of their pilots. They came from fluidic space, the extradimensional realm of Species 8472, and they resisted every Borg attempt at assimilation.
In Scorpion, Voyager found the Borg losing a war against the bioships, which could destroy cubes with a single beam and devastate a planet when several combined their energy. Janeway made a pact with the Borg, and the Doctor and Seven of Nine developed nanoprobe-based weapons that allowed Voyager to destroy bioships and drive Species 8472 back into fluidic space.
Bioships appeared again in Prey, when the Hirogen hunted an injured member of Species 8472 and Voyager was caught between them. Later, in In the Flesh, Voyager's contact with the species led to a tentative peace between the two sides.