Physiology and culture
It seems there may be a great variety among the Ktarian species. In some cases Ktarians have distinctive foreheads divided into two hemispheres (which seem to be bones), and distinctive yellow eyes with horizontally slit pupils. (TNG: "The Game")
In the case of a Ktarian/Human hybrid, the resulting offspring can lack the bony forehead structures and yellow eyes, and instead have exo-cranial ridges. A rare complication of these hybrid gestations occur when the baby shifts position in the uterus, and the exo-cranial ridges lodge in the uterine wall. A Ktarian/Human hybrid's gestation period is about eighteen months. (VOY: "Deadlock", "Fury")
Upon birth, breast feeding may begin immediately; however Human females must remain cautious, as the incisors of Ktarian infants erupt within three to four weeks of birth. Because Human females lack the scales of Ktarian females, alternative measures are typically recommended. The early stages of Ktarian development are marked by significant growth – a much higher rate of growth than that of Human infants. At the age of two, Naomi Wildman, a Ktarian/Human hybrid, grew five centimeters in a three-week period. (VOY: "Deadlock", "Mortal Coil")
The Ktarians are members of the United Federation of Planets, but in 2368 a rogue Ktarian faction tried to gain control of Starfleet. Their military power was insufficient to conquer it by force so they opted for an alternate gambit. They created a type of mind-control technology disguised as the highly addictive "Ktarian game", and attempted to use it in order to wrest control of Starfleet. The Ktarians almost succeeded in gaining control of the USS Enterprise-D but failed due to the efforts of Lieutenant Commander Data, Ensign Robin Lefler, and Wesley Crusher. (TNG: "The Game")
They also have some famous culinary dishes popular among Federation officers such as their Ktarian chocolate puff, Ktarian pudding, Ktarian eggs, Ktarian beer and Ktarian Merlot. (TNG: "Liaisons"; VOY: "Scientific Method"; Star Trek Generations)
List of Ktarians
In VOY: "The Voyager Conspiracy", Seven of Nine stated that "the Ktarians were officially with the Federation, but they sympathized with the Maquis". This suggests they may be a member of the Federation, however, they may just be allies.
There has been no official explanation for the obvious cranial differences between Wildman, Jol and the Ktarian drone.