A humanoid species who mate for life and who, under deep emotional strain, can unconsciously project a separate physical image of themselves, as seen in Second Sight.
The Halanans appear in the Deep Space Nine episode Second Sight. They are psychoprojective telepaths. In times of severe distress a Halanan can create, without knowing it, an independent figure that others can see and touch, and sustaining such a projection slowly drains the life of the person producing it. Halanans also take one partner for life.
In 2370 Sisko meets a woman called Fenna on the Promenade and is drawn to her, although she keeps vanishing. He then meets her double, Nidell, the wife of the flamboyant terraformer Gideon Seyetik.
Fenna is Nidell's projection, born of an unhappy marriage she cannot leave. Seyetik, who understands that she will die if things go on, pilots a shuttle into the dead star he has come to reignite. His death frees Nidell, and Fenna fades away. Nidell remembers none of it.