Beholders are omnivorous, genderless aliens, and a subject of great fascination for sages who study biology and the hunters who attempt to kill them. As such, a large amount of information is available on beholder anatomy.
Biological Features
The skin of a beholder appears to be made out of a stony substance, as strong and durable as steel, and just as inflexible. Upon death, the skin will harden further into a stone-like consistency.
Beholder 'bones' are incredibly porous and lightweight leather-like cartilage that is visually indistinguishable from their skin, but comparatively weaker, almost having the strength and durability of iron. Upon death, a beholder's skeletal structure will become brittle.
Their eyestalks are usually flexible tentacles, but varied among individuals and could instead be jointed stalks covered in rigid chitin or segmented stalks similar to the bodies of earthworms.
Not all beholders possess nostrils, those who do can breathe like humanoids, those that didn't can only breathe through their mouths.
A beholder's mouth is relatively similar to a humanoid's, but on a larger scale, containing soft palates, a muscular tongue and a row of upper and lower teeth, (averaging 56 teeth in total) lining a hinged jaw. Said teeth are long and thin however, designed for ripping and tearing rather than for chewing.
Beholders have one lung, and two stomachs.
Blood
Beholder blood is green. Unlike a humanoid heart that pumps blood around the body constantly, Beholders have a central 'blood sac' that, in conjunction with a powerfully muscled diaphragm, pushes blood into the Beholder's blood vessels, then pulls the blood back into the sac.
Brain
The Beholder brain is similar in appearance to that of a humanoid's, but wider, capable of reaching a diameter of up to 4 feet. Its two lobes, (known as "dweomerlobes") descend downwards to the left and right from the center like horns and have a complicated central nervous system surrounding it. The brain and nervous system is where magical energies are stored, amplified, and directed to the eyestalks. It has been observed that older beholder's brains gain ridges.
Diet & Digestion
While they require, on average, about 10 pounds of food and 2 gallons of fluid per day, an otherwise healthy individual could typically survive over twenty days without food or drink before dying of starvation or thirst. Additionally, a Beholder's digestive system is capable of storing excess consumed food to process as needed at a rate of 20 pounds per day. For example, if a Beholder ate 110 pounds of food, only 10 pounds of that would go towards its daily intake needs, and the rest would be digested over the course of the next five days without it needing to eat anything else. A Beholder can store at least 600 pounds of food in its stomachs at any time.
Food liquefies in the beholder's two stomachs and pumped through a intestine-like system up to the lung where these intestines thin out to a hair's breadth and mix the food with air. The Beholder's diaphragm pumps the digested food, combined with air from the lungs around the body, through a system of fine arteries to nourish the organs. Waste liquid, devoid of nourishment and oxygen, will then drain back into the mouth to be expelled or dribble out steadily.
Beholders can eat just about anything organic, but they do have preferences. They tend to enjoy eating small mammals and birds alive, (the combination sensation of soft flesh, crunchy bone and liquid blood in their mouths is considered a delicacy); gnomes; roast beef, lamb and pork; liver and brain pâté; insects; leafy vegetables, leaves, flower petals, and exotic mushrooms. Their favorite drinks are blood, wine, and food coloring. Visually impressive meals are always preferred, particularly colorful ones, (beholders often watch themselves eat with their eyestalks). They do not typically enjoy citrus fruits, grapes or melons; eyeballs; hard-boiled eggs; shellfish still in the shell; bull testicles; or anything fried in batter.
Indigestible items eaten by a Beholder will be either vomited up or absorbed into the body where it will eventually embed itself on the inside surface of the beholder's skeleton.
Eyes
The beholder's eyes are remarkable things. Hard, solid balls that draw in both light through the pupil and magical energy through the iris, which consists of some sort of translucent crystal. The shape of the iris can be anything the Beholder wishes, which grants it's owner both darkvision and exceptional vision in the light - Beholders in a brightly lit space had been observed as capable of counting the legs on a minuscule insect at distances of over one hundred and twenty feet. Beholder eyes also have up to twelve lenses, all capable of movement and rotation independent of the others, which is what grants them control over the aiming of their eye rays.
Further inside the eye is a mass of nearly invisible strands called evocularies. This nervous tissue transmits both light and magic into the three retinas at the back of the eye. The retinas then transmits the sensory signals and magical energy to the brain. When magic is needed to power a ray, the brain will send the magical energy back into the eye via the retinas.
Beholders gather the energy that fuels their magical abilities by observing spell effects, magical creatures and items. Without new magic to look at, Beholders can become very irritable, therefore they are driven to hoard magical items in their lairs and seek out magical places.
Probably the least understood aspect of Beholder biology is the antimagic properties of their central eyes. A Beholder's central eye emits a continuous antimagic field. Although careful squinting could narrow the area of the field generated, it will not stop unless the central eye's eyelid is completely closed, or the eye itself is put out or diseased to the point of uselessness.
Flight
A lighter-than-air gas is produced inside the bodies of Beholders. Some sages call this gas tiusium. Tiusium will collect in chambers in the body, concentrated mostly at the top of the skull, thereby ensuring that individuals will rest in an upright position. A Beholder will generate or expel the tiusium autonomically when it desires to ascend or descend. 360° tilting and horizontal movement is achieved through blowing air out of its lung via air vessels leading from its lung to its skin.
Life Cycle
Beholders are considered adults at the age of two years old and retain their vitality until their ninetieth year. After that milestone, most Beholders become increasingly frail and their abilities gradually cease functioning as they should. Most Beholders die of natural causes between the ages of one hundred and twenty and one hundred and fifty. Exceptions can be found in the elder orb subrace of the species.
At some point before the age of forty years, typically at the age of thirty, an egg-shaped womb swells below the back of the Beholder's tongue. This pregnancy causes extreme paranoia in the individual, until it gets so bad that the Beholder has to secret itself away in its lair until it gives birth. Prior to this, the Beholder will consume up to four times the amount of food it normally would to create a great enough reserve, as eventually, after around four months of pregnancy, the womb swells to a size too large to fit any food in its mouth. After just shy of six months of pregnancy, the Beholder gives birth.
The birth process has been witnessed by very few. According to those rare few witnesses, the Beholder will unhinge its jaw, spit up its womb and bite it off. The babies inside will then have to chew their way out. A Beholder brood is typically three to six babies, but could be up to twelve, with newborns being almost always one sixth the diameter of their parent. Newborns are birthed with the ability to levitate; possess strong racial memories and an inherent ability to speak Quevquel, though their eye powers will develop later.
The parent will choose one infant who looks most like itself to rear, and either eat or reject the remainder, forcing the survivors to fend for themselves. Since the birth process involves the destruction of the womb, Beholders can only become pregnant and give birth once in their entire lives. When the child that the parent chose to rear reaches adulthood, it typically rejects its parent and leaves to become independent.
Occasionally, a Beholder, while sleeping, will warp reality with it's subconscious mind and spawn a fully-grown beholder instantaneously out of nothing right there where it sleeps. If it is dreaming about itself, it may have created an exact duplicate of itself, otherwise it could spawn a beholder-kin or even a completely unique beholder-like creature.
Excretion
Beholders do not sweat or urinate. They do defecate, but their stool, which can be up to six cubic feet in volume, will become almost indistinguishable from a natural sedimentary rock within two days.
Senses
Beholders have a remarkable sense of sight, as mentioned. However, their sense of hearing is inferior to that of a human, and their sense of taste is notably poor, if not nonexistant. They primarily derive pleasure from eating based on the sight and texture of the food, rather than taste. One of the few things that Beholders can enjoy the taste of is alcohol, (though it takes well over 10 gallons of wine before they will get drunk).