An alien race from David Brin's Uplift sci-fi series of novels. The qheuen are crab-like creatures, with five claw-like legs arranged in pentagonal shape. As a qheuen also has 360 degree vision, thanks to a circular-strip vision cupola, there is no concept of 'forwards' for a qheuen, as one can move in any direction with equal ease. Qheuens are also very fond of water, generally living in coastal caves, or more rarely in freshwater habitats. Qheuens extract oxygen from air, but are able to hold their breath for periods over six hours. Their breathing vents are located on each of their five legs, which double as voice-boxes. Their bodies are covered in armoured chitin, and they are capable of retracting their head-segments when in danger, so as not to reveal their vulnerable sensory organs.

Qheuens come in three castes: the red, blue and gray.
The red qheuens are the lowest on the social ladder, being a slave-worker class. They are also physically the smallest, being on average only half a meter tall, and less than a meter wide. They are unintelligent compared to the blues and grays, begin very poor at abstract thought, and even when fully mature reason at a level comparable to a human 12 year old child. Reds also have a very short lifespan, lasting between twenty to thirty years on average.

Blue qheuens are, in their natural environment, the soldier class of the qheuen race. They are larger than the reds (about two meters across and under a meter tall, when mature),and are much stronger. They have a greater social standing than the reds, and have more mature minds from a human point of view, but still have trouble with abstract thought.

The grays are the ruling class of the qheuen race. They grow to a size larger than even the blues, but at a much slower rate. In their natural environment, all of the other castes are subservient to the grays. Grays are the only race of qheuens capable of thinking about abstract concepts adequately. Gray qheuens live for a very long time, in qheuen terms: up to a hundred years.

The society of qheuens is extremely rigidly class-based. As a pre-sapient species, the grays had complete control over the other classes. However, when their Galactic patrons Uplifted the qheuens, they forced the gray matrons to relinquish some of their domination over the other races of qheuens. Although there was widespread outrage in the circles of the grays, they had no choice but to accept the decision of their patrons. However, one faction of gray queens, not willing to face a society where they did not have total control, fled from their patrons in a borrowed sneakship, taking their slave red and blue qheuens with them. They landed on the fallow planet of Jijo, electing to live out their lives as savages and sooners, but keeping their old rigid hierarchical society.

Ironically, due to the intervention of humans and other races on Jijo, the lower castes have more freedom and equality than they ever had in Galactic society.

Qheuen reproduction is carried out entirely by the grays. The reds and blues are sterile and sexless. Large quantities of eggs are laid by the gray matrons, which hatch into larval versions of each caste. These shelless infants remain at home in the clan-hive until they undergo the molting process. When this happens, the larval qheuens' skins grow and harden, to form shells. However, there are many more larvae born every season than a colony can possibly support. So, with the ritual of molting, only a fraction of the infants can survive. The rest, the weakest, are killed in the orgiastic struggle to climb out of the nursery pool. From each generation of infants, only a handful can survive. According to Brin, the knowledge that, however well infants are cared for, the fate of most will be a tragic death lends a poignance to qheuen poetry that no human could ever comprehend.