Deacon

The Deacon — also known as an Proto-Xenomorph — is a Xenomorph-like species created by the Engineers (Space Jockeys) to be used as a weapon, which turns around and backfires horribly. It bears many resemblances to the Xenomorph; however, it possesses more human-like teeth and has an erect bipedal posture. Its head shape is also unlike that of Xenomorphs, and it seems to emerge from its host using its pointed skull as opposed to simply biting or punching through the ribcage.

It should be noted that the Deacon and its constituent castes are not the same species of Xenomorph encountered on LV-426; but rather a more primordial variant. LV-223 was the location of a facility housing prototypes of the black goo that would later bring life to this primitive form of Xenomorph.

Appearance
The Deacon's anatomy has distinct Xenomorph like features, but is still remarkably unique in comparison. Like other Xenomorph it is bipedal, Its head is also elongated but ends in a point. It lacks a tail and has no mouth-like tongue (as seen on the classic Xenomorph) but instead has a more primitive jaw mechanism where a second set of teeth slide forward and out of the mouth in a thrusting motion, akin to a goblin shark. It's skin/carapace resembles that of the Xenomorph by its reptilian/insectoid like appearance. However the Deacon has a distinct blue tone where as other Xenomorph have an almost black tone with very little colour.

Life Cycle
A Deacon is released into a host by a Trilobite. The Trilobite seen in the movie was gestated as a fetus within Elizabeth Shaw's womb, where it grew with frightening speed. It was removed via cesarean before it had fully grown and developed, yet it survived this procedure after Shaw leaves the area. She returns to see that although she removed the creature from her body it has grown immensely in size. The creature may be one of a kind since the Trilobite was a mutation.

The Trilobite has multiple tentacle-like appendages and skin that resembles that of a Facehugger. The Trilobite soon infects the Engineer with a tube-like organ that injects an egg/fetus through the Engineer's mouth. This behavior is similar to that of a Facehugger. It even dies after infection also like a Facehugger, indicating that the two are very likely related, though it has not been confirmed that this is so. The deacon embryo is orally injected by the Trilobite and, after a short while, the Deacon is born. It completely bursts from the Engineer, not just from its chest, but its entire front side, using its head to puncture and burst its way out of the Engineer's body.The deacon later got on a living engineer ship as the ship crashes on LV-426 later on turning into a queen alien and starts laying eggs and inpregnated the engineer.

Appearances

 * Prometheus (cameo, first appearance)
 * Aliens movie (but is the queen)