Tcerot
The tcerot (pronounced /ˈtʃɛrət/ or, more accurately, [ˈʈʂʰɜʁɞt˭]) is an ellogous life form found in the universe of Icathiria, though, like most Icathirian folks, it seems to have been originally brought there from another universe by the Stagehands. By itself, a tcerot is small, slow, and nearly helpless, but tcerots are able to control other creatures called ilasi apparently native to the same universe. Riding on the back of an ilasi, the tcerot can make use of the ilasi's limbs to get around and manipulate its environment far better than the tcerot can do so on its own.
The binomial name for tcerots used by Icathirian humans is Crotonas synetus.
Description
The smallest of the widespread folks of Icathiria, a tcerot typically measures a bit less than thirty centimeters in width and a bit more than forty in length, and about twenty centimeters dorsoventrally. It's shaped roughly like a human heart, with the narrow end at the front and a sharp crease running from front to back. Three short, curved legs attach to each side of the body. The tcerot has no apparent head, nor does it have prominent sensory organs. It does, however, have small pores all over its body that are visible on close inspection.
Tcerots are usually red-brown in color, though some tend toward brighter red or darker brown shades. About a hundredth of a percent are bright green, the result of a rare but mostly harmless mutation called pracinism. The legs are typically darker in color than the rest of the creature, and may approach black, though there is an uncommon genetic condition that gives some tcerots completely white legs instead.
Ilasi
Ilasi, the tcerots' mounts, have such importance to the tcerot's life that ilasi can be found wherever tcerots are, and vice versa. A tcerot is seldom seen off an ilasi unless it is asleep—and even then, many tcerots choose to sleep while mounted. An ilasi has six limbs, the middle pair large and stumpy and the other four longer but thinner and with digits capable of fine manipulation. Like a tcerot, it has no obvious head, but it does have a socket on the dorsal surface, the "sagma", within which a tcerot can ride. Unusually, an ilasi has two (approximate) planes of symmetry; it is symmetrical both laterally and anteroposteriorly.
While riding ilasi seems to be common in all tcerot communities, the details of how they relate to the ilasi differ. In some societies, the norm is for each ilasi to be the property of a single tcerot, who treats it as something between a pet and a personal vehicle. Tcerots may even name their ilasi, though the ilasi do not of course answer to those names. Some wealthier tcerots may own multiple ilasi, which they may use for different kinds of occasion, but it's very rare for a single ilasi to be used by multiple tcerots. In other societies, though, ilasi are more or less community property, and tcerots form no particular attachment to them; a tcerot from one of these societies thinks nothing of mounting any unattended ilasi nearby, and any given ilasi ends up being passed around between many tcerots. Where these tcerot societies predominate, there are common "garages" where ilasi are left when not in use, and from which any mountless tcerot is welcome to take them.
Though ilasi are by far the most common mounts used by tcerots, they are not the only ones. The evidence including the tcerots' own accounts suggests that the ilasi were the tcerots' original mounts, and probably the only ones that naturally coevolved with them, but tcerots later transformed some other creatures into potential mounts through bioengineering. Most of the tcerots' exotic mounts are related organisms from their own universe, but in some places tcerots have managed to engineer mounts out of organisms from other imperia. There have even been reports of some isolated tcerot communities making mounts out of other ellogous folks, though outsiders' reactions to this practice range from discomfort to condemnation.
Anatomy
The tcerot's body is divided sagittally into two parts, the left and right lobes. Externally, the crease in the surface of the tcerot makes the line between the lobes obvious; internally they are separated by a membrane called the mesoschideum. These two lobes are near-perfect enantiomorphs, only a few details breaking the tcerot's symmetry. Each lobe has a complete and almost entirely separate circulatory system, respiratory system, and even digestive system. Although there are some ducts and vessels that pass through the mesoschideum, they can all be sealed off almost instantly, and will be if one of the lobes is seriously damaged. This means that a tcerot can withstand serious damage to or even complete destruction of one side of its body, as long as the other side is intact. Over time, the damaged lobe will regenerate, and if it survives long enough the tcerot will be back to full capacity. Of course, in the meantime it may be severely impaired, especially if the damaged lobe is completely nonfunctional; most obviously, with only three legs all on the same side of its body, its mobility will be extremely limited.
The tcerot does not have a centralized brain; rather, the function is filled by ribbons of neural tissue threading all over its body. This distributed brain takes up almost thirty percent of the tcerot's volume, giving it perhaps the largest brain to body ratio of any Icathirian folk—though given the tcerot's small size, it may have been necessary for its brain to take up so much of its body in order for it to be large enough to support its intelligence and ellogy. More so than its other organ systems, the tcerot's brain and nervous system do work as one coherent unit through both lobes, although if one lobe is badly enough damaged the part of the brain in that lobe can still be severed. This does seem to hamper the tcerot's cognition and reflexes in the short term, but once it has regenerated the tcerot usually recovers its former faculties, though perhaps with some permanent memory loss.
Running down the interior of each leg is a neural fiber called a crural cord, which is protected by a rigid sheath and can be extruded through an aperture at the tip of the leg to interface with the nervous system of an ilasi or other suitable host when the tcerot is mounted, allowing the tcerot both to share some of its sensations and to exert control over its motion. Next to the crural cord is the Orlok duct, a tube that ends in a different aperture through which the tcerot takes in nutrients from ducts beneath the sagma of the mount. This is, in fact, the only way that a tcerot takes in alimentation; a tcerot that goes too long without attaching to a mount will starve.
The tcerot possesses two hearts on each side of the body, which pump its eiar through its veins and arteries. Each side of the body also has two lungs, which expand to draw in air through the respiratory pores on the tcerot's surface. The tcerot's digestive system is very simple, consisting of little more than a couple of digestive tubes through the walls of which nutrients are absorbed into its eiarstream; the nourishment the tcerot takes in through the Orlok ducts is for all practical purposes already digested.
Senses
Although the tcerot's sensory organs are not obvious, it does have tiny eyes studding its body. Although it's not uncommon for tcerots to have different configurations due to various genetic conditions, most tcerots have twenty-eight eyes, fourteen on each lobe. These eyes are not spherical like human eyes, but shaped like tapering tubes, mostly contained within the tcerot's body with only the rounded ends visible at the surface—the closest Terran analogue would be the eyes of the jumping spider. Acting much like a tiny telescope, each eye individually has a high resolution but a very limited field of view; the large number of eyes, which can be independently rotated and directed, compensates somewhat for the latter deficiency.
The tcerot does have hearing organs, but they are even more inconspicuous than its eyes. A typical tcerot has ten auditory apertures, five on each lobe, but they are covered by skin and undetectable externally except peprhaps by the faint outline of the aperture's edges. The disk of skin covering the auditory aperture is called the tympanum, but it is continuous with the surrounding skin and structurally little different from it. Within the auditory aperture are delicate hair cells that detect the vibration of the air within. A subcutaneous operculum closes off each aperture when necessary to protect its internal structure. Because the vibration within the auditory aperture is somewhat muted by the tympanum, a tcerot's hearing is poor; while it can hear a wide range of frequencies—from roughly ten Hertz to 120 kilohertz, it has trouble detecting sounds below fifty decibels in volume, or responding to rapid changes in either frequency or volume.
While mounted, a tcerot shares the senses of its mount in addition to retaining its own. An ilari's vision has a lower resolution than a tcerot's but a wider field of view, while its hearing encompasses a smaller range of frequencies but is otherwise significantly superior. Most unmounted tcerots have no sense of smell or taste, but while mounted they can share these senses of their mount. Interestingly, it seems that tcerots ancestrally did have a sense of smell, through olfactory receptors lining the outer parts of its respiratory ducts, but this trait was lost at some point in their evolution. The genes, while inactive, have not been entirely removed from the tcerots' genome, and occasionally a tcerot is born with an atavistic rudimentary sense of smell, a phenomenon known as palæosmia.
Reproduction
Though when interacting with gonochoric folks like humans some tcerots may choose to identify as male or female, tcerots are biologically hermaphrodites, each individual producing both male and female gametes. Within the tcerot's cloaca are both an intromittent organ called an ædeagus and an ovipore into which the ædeagus is inserted. During copulation, two tcerots line up their cloacæ and each simultaneously extends its ædeagus into the ovipore of the other. (Because their cloacæ are located on their ventral surfaces, tcerots cannot copulate while mounted.) Fertilization is not guaranteed, and the copulation may result in the impregnation of either, neither, or both of the participating tcerots.
In most tcerots, the ædeagus is located on the left side of the cloacal cavity, and the ovipore on the right; two tcerots can therefore line up their parts correctly by facing the same direction during copulation. Like humans, however, tcerots may be subject to complete or partial situs inversus, which may result in the positions of the ædeagus and ovipore being reversed. It is possible for two tcerots of opposite visceral situs to copulate, but in order to do so they must face opposite directions, lining up head-to-rump.
If fertilization is successful, one or more spherical, pearlescent eggs grow within the ovary of the impregnated tcerot. Usually a tcerot grows only one egg at a time, but a little less than one time in three there are two eggs, and about one in ten times there are three or more. The most eggs that a tcerot has ever been recorded laying at once is six. The eggs are carried inside the tcerot's body for about three months before being laid, whereupon an additional three months typically passes before they hatch. The newborn tcerots are tiny and helpless and carefully tended by their parents; a tcerot takes about twenty years to reach full maturity, but—much like a human teenager—achieves some level of self-sufficiency before then.
Society
Tcerots are highly social creatures, and prefer to live in large groups. Solitary tcerots are not entirely unknown, but are definitely the exception to the rule, and often have other idiosyncrasies as well. However, tcerots bond easily with other folks, and thrive at least as well in mixed-species communities as in those made up entirely of their own kind.
Tcerots have a reputation for inordinate fondness of categorizations and taxonomies. This reputation is frequently exaggerated, but it's true that tcerots do often draw distinctions that humans and most other folks do not, and are reluctant to conflate matters that other folks see as just variations of the same concept but that tcerots see as distinct. One of the most widely cited examples is the tcerot take on friendship. Tcerots often form deep and lasting nonfamilial relationships, but most tcerot languages have different words for different kinds of such relationship, all of which a human would likely just call friendship—and in fact when these concepts are translated into English or other human languages, they generally are just referred to as different kinds of friendship, though the tcerot words for them are dissimilar. Though most tcerot cultures do recognize multiple such relationships, the exact set of relationships varies, but some that seem to be universal, or nearly so, include "like friendship", friendship stemming from common interests the friends can talk about or jointly partake in; "balance friendship", friendship in which the two friends each have skills or characteristics that compensate for lacks in the other; "aspirational friendship", in which each friend has traits the other admires or wishes for; and "comfort friendship", a relationship that has developed gradually over long acquaintanceship and is not based on any specific characteristics. To the tcerot, these are all very different kinds of relationship, and many tcerots find the fact that humans (and other folks) don't have different words for them confusing and unsatisfying.
With the exception of a few unusual cultures, tcerots do not mate for life, and only the "mother"—parent who laid the egg—raises the child and maintains a close relationship with them in their adulthood. It's far from unknown for the "father" to also keep in touch with the child and the mother, but it's not routine or expected, and very rarely are they as close to the child as the mother is. It is however, common for tcerot mothers to ask acquaintances with no blood relation to help raise the child; in English these volunteer coparents have come to be called godparents, though the tcerot relationship lacks the religious connection of the relationship to which that word was originally applied. It is certainly possible for a tcerot to turn down the request to serve as a godparent, but it's rare; tcerot mothers generally only ask those they are already close to and whom they expect to accept the request. Godparents may have children of their own, and it's common for two tcerots to simultaneously be godparents of each other's children and for those children to be raised together. Typically a tcerot child will be raised by one to four godparents, in addition to its mother.