Symbiotic life forms presumed to originate at the other terminus of the Silis system Matryeshka Drive. According to one of the Coality merchant officers of the YAG Kyle Lattimer compromised by a symbiote, their home volume is in the Hook Rift, leading to the name "Rift Symbiotes". Their actual origin is not known.
The Rift Symbiotes are the only known sentient symbiotic life form. They seem to be compatible with both the Silis Xenomorphs and humans, with an apparent preference for the latter. This ease of symbiosis across highly divergent life forms is unique in known space and history. There is some philosophical speculation that the Symbiotes are not a life form at all, but a mind-machine interface enabling intelligent beings' latent talents.
Impact on Humans
Note that the following evidence comes from sixteen known Rift-Human symbiotes. As such, it is not known what is due to individual variation.
Once inhabited, humans go through a transition period of roughly 48 hours. The infected individual may become comatose, disoriented, delusional, or (rarely) exhibit little or no symptoms. During an episode of mass infection aboard the derelict merchant vessel, the transition resulted in violence and death as the disoriented crew —both infected and not— struggled to adjust to the invasion.
In the humans' case, the abilities, knowledge, skill, and power hierarchy were all preserved. The ship's captain remained in command, the first officer continued her duties as operations officer, and so on. However, it is noticed that many of the sixteen Rift-Humans took up unusual hobbies or behavior, usually in the form of creative expression, mysticism, or mania such as paranoid schizophrenia.
Humans in a symbiotic relationship need little sleep. Evidence of insomnia exists in recordings, as does insomnia-induced cognitive failure. Rift-Human symbiotes resorted to sleep meds to compensate.