Reptilian humanoids with advanced holographic technology, one of whom unexpectedly left Trip Tucker pregnant.
The Xyrillians are a reptilian humanoid species who thrive in conditions that humans find harsh and who possess advanced holographic technology. Their reproduction can involve hosts of other species, a fact that took Enterprise's crew by surprise.
In Unexpected, Trip Tucker helped repair a Xyrillian ship and grew close to the engineer Ah'Len, and a game they shared left him unknowingly pregnant. To get help transferring the embryo, Archer tracked down the Xyrillian ship, and the Klingons obtained Xyrillian holographic technology during the encounter.