Devidian

Devidians were a vaguely humanoid, shapeshifting species native to Devidia II. Their physical characteristics composed of being between 2 and 3 meters in height; they had no apparent eyes but they possessed an orifice on what most humanoids would call their forehead, that resembled a mouth. They lived out of phase with most other lifeforms with a phase variance of 0.004. They also possessed the ability to travel through time.

Devidians' only useful form of nourishment was Human neural energy. They acquired this energy by draining the subject of their neural energy, killing the subject. They preyed on Humans from 19th century San Francisco using the cholera epidemic at the time as a cover for their murders.

In 2369, the USS Enterprise (NCC-1701-D) fired modified photon torpedoes on the Devidians' cavern habitat to prevent them from further incursions. 

List of Devidians

 * See: Unnamed Devidians

Apocrypha
In Star Trek Online, set forty years after "Time's Arrow", the Devidians return in a five-part feature episode series, where they have been spotted in the re-established Klingon Neutral Zone. Player captains of both the Federation (working for Section 31) and the Empire (working for Klingon Intelligence) are sent to investigate. The Devidians' appearance has been changed to make them look more like ghosts, with them hovering above the ground and being partially transparent, and they are led by a leader referred to as the Shrouded Phantasm.

Devidianer Devidien