Species 571 was the Borg designation for a race of the Delta Quadrant who worshiped a god named Brothara. They were a humanoid species distinguished by a bifurcating (cartilaginous) ridge running vertically down the forehead stopping at the upper lip.
In their religion, it was considered "against the will of Brothara" to desecrate a dead body. P'Chan also noted that his "people don't believe in holding grudges."
Members of this species came into contact and were assimilated by the Borg sometime before 2368, when a Borg sphere crashed on Planet 1865-Alpha, severing the three surviving Borg drones from the Collective. Among the drones were P'Chan and Lansor, both of whom managed to escape the Collective permanently some time before 2376. (VOY: "Survival Instinct")