The Saruthi are an alien race briefly encountered in the Eisenhorn trilogy of novels. In fact, their appearance is one of the rare occasions that Eisenhorn comes into direct conflict with an alien species, which is rather odd given that he's a member of the Ordo Xenos. Moving on...
The Saruthi are an ancient race, and prior to the rise of the Imperium they held a small empire of about forty worlds. At some indeterminate point in history the Saruthi made first contact with humanity in the form of some poor, persecuted humans of a maligned minority religion who were fleeing human space. These pilgrims blundered into Saruthi space and brought with them the Necroteuch, a powerful reservoir of Chaos knowledge. Translation efforts went underway and soon the Saruthi had a version of their own.
The Saruthi saw the arcane knowledge contained within the Necroteuch as their means to fend off the much more powerful Imperium. While the Saruthi civilization did indeed survive (after a fashion), the Necroteuch extracted a horrific price. The Saruthi were far more susceptible to the artifact's corruption than their human counterparts; its effect on them was so powerful that their souls, minds, and even their genetic codes were irrevocably altered. A civil war also erupted, although it is unclear whether this was a Chaos-driven power struggle or whether some of the Saruthi finally realized that the price of using the Necroteuch was too high to pay. In the end, it mattered not; the Saruthi empire was drastically diminished. And while the Necroteuch had taught them how to bend reality itself, the remaining Saruthi were reduced to twisted, mutated, vile creatures.
What remained of the Saruthi civilization survived in this manner until the end of the 41st millennium. In a final cruel twist of fate, it was their possession of the Necroteuch (and by extension, their exposure to Chaos) that eventually drew the Imperial Inquisition's attention and led to the destruction of what was probably the only inhabited planet they had left.
Biology and Abilities
The Saruthi of the 41st millennium are grotesque beings. Humans encountering them for the first time are often deeply horrified by their powerful, yet clearly unnatural forms. The average Saruthi, if there is such a thing, is approximately two meters tall and twice as heavy as a male human. Their bodies are vaguely crustacean or arachnoid in appearance, with a flat, gray torso, a thick, boneless neck, and a rather oblate, eyeless head. Their five limbs are arranged around their bodies in an asymmetrical, seemingly random manner. They use human-like digits at the ends of these limbs to clutch silver walking stilts, which enhances their height even further. Even the manner in which the Saruthi walk is disturbing, because their limbs do not ambulate in any particular sequence.
When communicating with humans the Saruthi interlace their fingers to form an extremely unnerving representation of a human face, just like the creatures in every Guillermo Del Toro movie. They also possess an inherent ability to discharge powerful energy bolts. Fortunately, the Saruthi are still living creatures and are thus vulnerable to physical damage. They bleed a grey fluid when wounded.
The Saruthi lack any sense of sight or hearing. Instead they perceive the world through extremely developed senses of touch, smell and taste. Their exposure to the Necroteuch allows them to perceive and work with four-dimensional spaces called "tetrascapes." Being a four-dimensional construct a tetrascape possesses an unnatural and disorienting lack of symmetry that is very unpleasant for humans to experience. Since the Saruthi lack starships the tetrascapes serve as their manner of travelling between worlds, much like the Webway, although how they accomplish this feat is not understood.
The Saruthi were observed utilizing a lesser slave-race that vaguely resembled the Saruthi themselves. Whether these were the debased descendants of the losers in their civil war or were a different species entirely is not known.
During the events of the Eisenhorn trilogy the Saruthi world of 56-Izar was invaded by an Inquisitorial task force in order to destroy the Saruthi's copy of the Necroteuch. After the artifact was destroyed the planet was subjected to Exterminatus. Following this event no further contact ever occurred between the Imperium and the Saruthi. Given their already diminished population and their adverse reaction to the destruction of the Necroteuch itself (insofar as it could be observed in the moments before their world was destroyed), it is likely that the Saruthi were completely annihilated.