What we wind up with is a race of four-armed reptilian creatures that have a very different silhouette and profile than other alien races. The Tzenkethi employ modular and adaptive technology, but they tend to favor the same strategies time and again, and the designers stress that your first encounters against them should prove the most difficult. So they’re going to be a different sort of foe on all levels, not just in the sense of looking different. Pretty good for a species we only heard mentioned in the background by Captain Sisko.
Source: Official Site