Axum's species was a humanoid species, some of which had been assimilated by the Borg by 2377. (VOY: "Unimatrix Zero, Part II")
Although not directly stated, Ravis and Axum share the same make-up. Axum's species has a spoon-shaped depression on the forehead, much like the Cardassians.
The novel Acts of Contrition calls this species the "Mysstren" and reveals that they have low-level psionic abilities.