The Praetomorph (Plagiarus linesteres) was a genetically-engineered species of highly-aggressive endoparasitoid that bore a great resemblance to the Xenomorph XX121 species. Originally the result of experimentation carried out by the rogue Weyland Corp synthetic David, initial incarnations of the Praetomorph were loosed on the crew of the Weyland-Yutani Corporation colony ship USCSS Covenant in 2104. Human encounters with the species did not stop there, however; Praetomorphs also emerged on the worlds of LV-187 and Shānmén during the Frontier War.