The Nemacyte was a bipedal enemy only found within the Rift Worm. The Nemacyte is the Rift Worm's secondary means of destroying living organisms within its stomach area, the primary force being its digestive teeth. They are medium sized, about the size of a Gear soldier, being 6 feet from head to tail. Their bodies consist of a rounded trunk, with two large, pincer-like legs used for movement. For stability, the Nemacytes have a tail that extends from their body and trails behind them as they crawl along on their legs.
The Nemacyte is spawned from small holes inside the Rift Worms stomach and usually travel in small groups, consisting of only three or four at a time. They move quickly and once they begin attacking they are hard to remove as they attempt to eat their prey. Nemacytes, however, are incredibly weak health-wise. A small burst from the Lancer Assault Rifle is enough to kill them.
They seem to live just under the surface of the worm's stomach, emerging from holes that open up in the ground. They also appear to have some acidic-based quality, as Benjamin Carmine seemed to have acid all over him after being mauled by them, but this could be because he was thrown into the worm's digestive tentacles that cover most of its stomach.
- "There's something up ahead!"
- — Marcus Fenix after seeing a Nemacyte emerging from a hole.
As Nemacytes live in the Riftworms stomach, it can be assumed that they have existed as long as Rifworms have, it is unknown wether or wether not if the COG or the Locust had some knowledge about this creatures before Operation Hollow Storm, in which Delta Squad was eaten by the Riftworm and as they entered the uvula, they began to see Nemacytes emerging from the ground. After dispatching a small group, they saw a trio of them attacking and attempting to eat Ben Carmine, the gears shot at them before they could eat him and fled, Carmine would later die from his injuries, as they progressed through the worm they found more Nemacytes trying to prevent them from destroying the Rifworm's hearts, however they failed and the Riftworm died, presumably all Nemacytes died with it.
- Nemacytes appear to serve the same function as White blood cells, in that they protect the body from possible infections.