Ambate
An ambate (pronounced /ˈæmbeɪt/ or /ˈæmbət/) is a creature with a horizontal posterior section and a (more or less) vertical anterior section. The two sections may or may not resemble the posterior and anterior parts of two existing creatures (the former with horizontal posture and the latter upright); if they do, the creature is called a conjunct ambate. A conjunct ambate with the anterior part that of a human (from the waist up) is called a centaur.
So well known is the centaur on some worlds, in fact, that it is taken as the paradigmatic type of ambate, and ambates in general are known as "centauroid" or "tauric" creatures, or simply as "taurs" . None of these terms, however, is accepted by a majority of etorists, and the last two in particular are etymological teratisms; the derivation of the original Greek word κένταυρος from which "centaur" is descended remains uncertain, and there's no good rationale for taking only its second half to form a new word. (Then again, a similar argument applies to the prefix "cyber-", which is a similar affical product of metanalysis.)
The associated adjective is "ambatic" (/æmˈbætɪk/). The word "anambatic" (/ˌæanæmˈbætɪk/) refers to creatures that are not ambatic in form, but is rarely used.
The word "ambate" is commonly, but erroneously, associated with the prefix "ambi-", meaning "both", in presumed reference to the fact that it combines the forms of two creatures. In fact, "ambate" comes from the Greek word ἀμβάτης, a variant of ἀναβάτης, meaning a horseman or rider, in reference to the resemblance of an ambate to one (upright) creature riding on the back of another (horizontal).
Anatomy
Because ambates in effect have two torsos, or at least one and a half torsos, special considerations apply to their anatomy. Many ambates have either unusually large and strong hearts, to pump blood into the full length of their sesquiplicate bodies, or multiple hearts, often one in the vertical part of their bodies and one in the horizontal. Various glands and other organs are also similarly enlarged and/or duplicated—including the lungs, if applicable, the better to supply the needed oxygen (or other effects of respiration). Some ambates even have separate brains, or at least ganglia, in the two parts of their bodies, though this is relatively rare.
Because of the ambate's dietary needs to adequately supply its elongated body, ambates often have unusually large heads, or at least unusually large mouths and gullets. Where they do not, ambates still often must spend an inordinate amount of time eating. This is certainly not universally true of ambates, however; others meet their dietary needs by having unusually efficient digestive systems, by photosynthesis or other methods of gaining energy to supplement that gained by digestion of food, or even by relying partly on magical sustenance.
In the case of ambatic mammals, the umbilical cord may connect to either the horizontal or the vertical torso, depending on the particular species; where the umbilical cord connects will, of course, determine the location of the navel. Some mammalian ambates, in fact, have two umbilical cords, and as a result have two navels, one on each torso, but this is relatively unusual. Still others have a "false navel" on the torso that does not connect to the umbilical cord; in some cases this false navel serves a different purpose (e.g. a supplementary orifice for respiration), but in other cases its purpose remains mysterious.
Classification
The word "ambate" only refers to a general body shape, and tells nothing about the taxonomy of the creatures involved. Within the ambatic form, a limitless amount of variation is possible. A few kinds of ambates, however, are common enough to merit their own terminology.
Conjuct ambates are those combining the posterior form of one creature and the anterior of another, the centaur being a well known example. Also fairly common are ambates in which both the horizontal and vertical parts correspond to the same creature, with the torso duplicated. This generally involves some modification, either to the horizontal part to give it a quadrupedal gait if the original creature is upright, or to the upright part to slim it and perhaps give it prehensile arms, if the original creature has a horizonal posture. Such an ambate is called a borew. (Technically, a creature with the horizontal and vertical part human—a boman—would be both a centaur and a borew.) There are also ambates in which either the horizontal part or the vertical part resembles some other creature, but the other part does not; these are sometimes called demicentaurs.
Ambates are also sometimes classified by their number of limbs. The most common ambatic form has four walking limbs on the horizontal part and two manipulating members on the vertical part; such an ambate is called a 4-2 ambate, or sometimes a limminate. One with six limbs on the horizontal part, and two on the vertical part is called a 6-2 ambate or an asminate, and one with eight limbs on the horizontal part an 8-2 ambate or an usminate. An ambate with a great number of limbs on the horizontal part (such as, perhaps, a conjunct ambate with the horizontal part that of a centipede) is called a sarminate. On the other hand, an ambate with four walking limbs on the horizontal part and four manipulating members on the vertical part is called a 4-4 ambate or a limingate. There are, of course, many more possibilities than these. The limb count of any sort of ambate can be specified by two numbers separated by a dash, the first number representing the number of limbs on the horizontal part and the second on the vertical part, but there are also special words for each combination. The following table summarizes most such words accepted by the etorical community, although it should be pointed out that most of these words are not in common use even by etorists, and that many of them correspond to hypothetical combinations no actual examples of which may be known to exist. (In fact, there are many etorists who see this proliferation of words to define ambates by their limb count as unnecessary and ridiculous, and move to the suppress them.)
Of course, since ambates are an ataxonomic designation, ambates can also be classified by their etorical taxonomy. Mammalian and reptilian ambates are relatively common, but ambates can also be arthropodal, or belong to their own classes and phyla, among other possibilities. Of course, conjunct ambates may combine features of multiple taxa.
Origins
Most types of ambates are simply natural organisms that happened to evolve into an ambatic form, just as other species happened to evolve a "normal" horizontal or vertical form, or a serpentine form, et cetera. Such ambates may reproduce by ordinary sexual procreation, and in other ways have life cycles comparable to those of related anambatic species.
Other ambates, however, were the product of genetic tampering, magical transfiguration, or other artificial processes, or were simply created more or less ex nihilo. As with other cases of eidogenesis, this may have been an intentional act, or may have been an unplanned accident. Many conjunct ambates, in particular, may be either (magically or technologically facilitated) hybrids of two very different species, or the product of henosis of individuals belong to said species.
Related forms
A creature with an upright posterior section and a horizontal anterior section is called a gammate. Gammates are much rarer than ambates, no doubt in large part because of the balance issues involved. To avoid falling forward (or backward or sideways, in the even rarer case of gammates whose horizontal part projects in a direction other than forward), a gammate relies on either magic, a very heavy tail or other counterbalance, or long legs or supports on the horizontal part.
Also rarer than ambates are creatures with an upright part arising from the middle or back of the horizontal part, rather than from the front like an ambate. While some etorists consider these simply varieties of ambates, calling them respectively medial ambates and posterior ambates (as opposed to anterior ambates), more commonly they're considered distinct from ambates, and called leucions and urodemes. Yet another creature form similar to the ambate, the anticorm, has a vertical part on each end of the body. Most anticorms have legs so arranged as to make them capable of walking in either direction with equal facility.
In fiction
The vast majority of ambates in fiction have been centaurs. More specifically still, the vast majority have been hippocentaurs, centaurs with the horizontal part that of a horse. Centaurs other than hippocentaurs existed in mythology, but are rare in modern fictional literature, though they do proliferate in some role-playing games.
Non-conjunct ambates, however, while uncommon in fiction, are not entirely nonexistent. Dungeons & Dragons includes the quaraphon, the drakkoth, the thorciasid, and the uvuudaum; Traveller had the K'kree;Warhammer 40,000 in its first edition had the ambatic zoat; and one of the s in GURPS Fourth Edition is an ambatic robot. Mounted demons in the Japanese manga/anime series Berserk merge with their mounts into an ambatic form that does not resemble a mere conjunct of its components. the video game Oddworld: Stranger's Wrath had the ambatic Steef, and the Elder Scrolls video game series had the land dreugh (not to be confused with the accorine "true" dreugh of which the land dreugh is apparently a temporary metamorphosis). Ambatic aliens have made appearances in some science-fiction stories, including Poul Anderson's Ishtarians and Donarrians, Robert A. Heinlein's centaurs of Charity, Edward M. Lerner's F'thk, Jerry Pournelle's centaurs of Purgatory, John Ringo's Posleen, James White's Duthans, Walter Jon Williams' Naxids, and the Andalites from the Animorphs series (though admittedly some of these are depicted as rather similar to conjuncts of Euterran beings).