Trilobite (Prometheus)

The Trilobite is a creature derived from the Black Liquid of the Mala'kak.

The liquid, when ingested by Dr. Holloway, spreads through his system within a 24 hour period, breaking down his DNA as it physically changes him. Before realizing the changes taking place in his body he and Dr. Shaw had intercourse whereby transmitting some of the changed DNA to her in the form of sperm. She soon became pregnant. However, before the rapidly growing alien inside her expanded and killed her, she had it surgically removed via an advanced device on ship. The creature, presumably dead, shows back up at the end of the movie resembling a massive facehugger which grapples with and impregnantes the Mala'kak with the first xenomorph species, the Deacon(termed "Proto Alien" by several online references).