As might be expected in a guide to Niralans written by a physician, a significant chunk of Niralans: An Overview is dedicated to the species’ biological distinguishing features.
Here’s part of that info.
From Niralans: An Overview, by Makkarah Tomorah (Atalanta University Press, 2350).
Niralans are a humanoid species with white or slightly blue-tinged skin, black or dark blue eyes, and black hair. Adults average 170 centimeters in height, although adult heights may range from 150 to 195 centimeters.
Distinguishing Features: Niralans are most easily distinguished from similar species by the kiiste, consisting of one to six keloid skin-surface ridges running down the right side of the body on both the dorsal and ventral aspects. The ridges are black in color and stand in stark contrast against the species’ white to blue-white skin. It is believed that the development of the kiiste offered an evolutionary advantage on the Niralan landscape, which is primarily arctic in nature, by breaking the visual line of the body and making it more difficult for predators to recognize.
Despite variations in pattern, the kiiste consistently begin at the crown of the head and proceed down the right side of the body in one or more continuous lines, ending at the top of the foot. The left side of the body is unmarked, as are the palm of the right hand and the sole of the right foot. Kiiste patterns are inherited along family lines, with children displaying the same pattern as the parent (see “Reproduction”).
The Niralan hand is five-fingered and bilaterally symmetrical (minus the opposable thumb) with an articulated central vertebral line. The foot displays a similar central line, but the relative inflexibility of the ankle joint limits the foot’s range of motion somewhat. The fingers are four-jointed and typically half again as long as the palm.
The eyes are typically black or dark blue and may be unusually large or wide-set. Hair colors range only slightly, from true black to blue-black; individual hair strands are unusually thick, and the hair can support a significant amount of weight before breaking. The inside of the mouth and the mucous membranes are frequently purple or dark blue.
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