It's interesting because for the Neomorph although the Pods act like Eggs, the Motes act as the Facehugger, they actually disappear into the host (although they may also die inside after serving their function) as depositing the mutagen.
In this way the Trilobite's closer to a Facehugger functionally using a human being's ovum with sperm as the Egg.
But it makes me wonder if Plagiarus Preapotens, and the Plagiarus Linesteres, exist basically as forms of The Pathogen itself programmed to perform a specific purpose.
Meaning that the Motes probably deposit "Plagiarus X" let's say.
And that the Trilobites probably deposit "Plagiarus O" for example.
In the way this applies to the main Alien species with the three types of Egg and Facehugger we now know of.