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Description
The most charismatic of R'lyehian fauna are the ones which bear the most overall familiarity of vertebrate amniotes found elsewhere in the world. Which is to say, still very little, for other than possessing a bony endoskeleton and moving on jointed limbs, there are only a few superficial similarities. Xenotherians are a group of mollusks, likely related to gastropods, which evolved from a marine ancestor isolated on the proto-R'lyehian continent over five-hundred million years ago (some studies suggest a possible ancestry from helcionelloids, but the relationship is controversial) and all known species are still entirely endemic to the corpse-isle. Crown-group xenotherians likely appeared much more recently, which most evidence suggesting the most recent common ancestor of all living species evolving during the Early Mesozoic. Since then, they've adapted to the changing conditions down vaguely analogous lines as vertebrates, although anatomical differences are vast between the two groups.

Ancestral xenotherians have six legs, although one or more pairs have been modified, reduced, or entirely lost in some species. The eyes are mounted on muscular turrets, giving most species a very wide range of sight, and nearly all xenotherians are primarily vision-based navigators. Most xenotherians tend to be vividly coloured and patterned and many have the ability to change their skin pigments, although the degree of this ability's complexity varies from species to species. Their skeletons are comprised of a chitin and calcium carbonate composite, while the hair-like filaments which cover their body are evolved from the protein conchiolin fibres found from on the mantles of many molluscs. To assist in navigation and orientation of three pairs of legs, two secondary ganglion masses occur in the middle and posterior body portions which assist in controlling autonomous functions of the lower body. The face consists of six muscular palps, which in some species have been modified into horns or prehensile tentacles, or fused together. Their blood is a milky magenta or light purple when oxygenated due to being comprised of a protein matrix of hemerythrin and hemocyanin, which is pumped through the body by an anterior and posterior heart.

Over some two-hundred or so million years, the first xenotherians evolved into dozens of species of widely varying forms and lifestyles, from vicious fang-mawed hunters, bizarre tall-bodied browsers, worm-like burrowers, herd-dwelling grazers, winged scavengers, rat-like creatures weighing only a few grams to hulking beasts over one ton, and everything in between.

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MAJOR GROUPS OF XENOTHERIANS*

TEDDIES: The basalmost group of living xenotherians, and likely represent what the original ancestors of all modern species descended from. Distinguished by six walking legs of equal length and a sprawling reptilian posture. All species retain four claws on each foot, resulting in a zygodactyl foot arrangement, have a thick hairy coat, and reproduce through oviparity. All species are predaceous, but have a moderately generalist diet. Because of their thick coat, their colour-changing abilities are limited. Group represented by the grizzly teddy.

SQUID MONKEYS: A group of primarily arboreal, six-legged xenotherians, with degeneration of the mid-ganglia allowing for a more flexible body. The front pairs of palps have been elongated to tentacle-like grasping organs, while the bones inside the two front pairs of walking appendages have greatly degenerated for greater agility while moving arboreally, sacrificing ground mobility. All species are excellent climbers and adapted for vertical environments. They retain all four claws, allowing them to grasp branches, cliffs, and vines easily. The range of movement among them is the most varied of any xenotherian group, with species capable of hexapodal, quadrupedal, and some even very limited biped motion. Group represented by the thogg.

URCHIN-HOGS: Hexapodal xenotherians that are primarily pseudo-herbivorous, they are so named for their spiny coats of bristling spines, which can anywhere from subtly hardened hair to a vibrant coat of huge quills and curved bony spikes. In some species, these are enhanced by toxic secretions, while others rely on the durability of hardened spiky armour derived from the hairs. The tongues have been adapted into radula-like grinding organs used for chewing and can no longer project from the mouth, and so the lower pair of palps have been adapted into prehensile graspers to compensate. These are egg-layers, although some retain the eggs inside their body until they hatch; all species produce infertile eggs to feed their young. Group represented by the burr boar.

DRAGONWINGS: A clade that has evolved powered flight, with skin-membrane wings derived from their front and middle limbs, and an exceptionally large and complex lung cavity to take in oxygen. In the ancestral species, there was a thin tail to balance, which has been lost in many species. In some species the two pairs of wings have become fused into a single pair of wings. The last pair of legs retain four-claws, while the mouthparts have been heavily altered in numerous lineages to reduce weight to the head; however, some are flightless. Smaller species tend to be bipedal, although larger species may bear some weight on the wings on all sixes as well. Group represented by the skincrow.

STRIDERS: One of the most morphologically distinct subgroups of xenotherians, these are specialized browsers which have evolved extremely elongated upper bodies, creating a roughly humanoid, upright form that still walks on four legs (with the front pair of limbs used as manipulator arms). The tongues of the striders have become elongated, muscular appendages used for manipulation similar the trunk of an elephant with the arms and legs so far from the head, with enlarged storage sacs in the upper "chest" behind the face where they are kept at rest. Most species have some type of fleshy lobes over their upper body which are used for display. Group represented by the star strider.

BLISTER-BEASTS: Quadruped xenotherians that are primarily pseudo-herbivores, in the group one or more pairs of palps, as well as the front appendages in some species, have been adapted into horn-like structures used for display and/or defence, with a variety of fantastic ornamentations. They are named for special glands on parts of their body (the location of which varies from species to species) that allow them to shoot potent vesicant compounds for defence. Their more compact bodies compared to urchin-hogs allows them to run faster but sacrifices agility. They grow a type of fatty, nutrient-rich tissue on their undersides when rearing young as food for them. Group represented by the black cattle.

WRATHRATS: Sometimes considered to be the corpse-isle’s equivalent to rodents, this is a grossly oversimplified, if not entirely inaccurate description. Their name comes from their relatively small size and ever-growing hard beak at the front of their palps (functioning analogously to a rodent’s incisors), although neither attribute is universal. Although closely related to the grazing blister-beasts and more distantly related to the browsing striders, these are mostly predaceous and many are notoriously vicious hunters. All members are quadrupedal, with the front pair of limbs modified into grasping appendages. Group represented by the banshee.

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*Branches designated with a plural have several members; those that are singular only have just one or two species total, representing only minor, but still notable offshoots.

Description
The most charismatic of R'lyehian fauna are the ones which bear the most overall familiarity of vertebrate amniotes found elsewhere in the world. Which is to say, still very little, for other than possessing a bony endoskeleton and moving on jointed limbs, there are only a few superficial similarities. Xenotherians are a group of mollusks, likely related to gastropods, which evolved from a marine ancestor isolated on the proto-R'lyehian continent over five-hundred million years ago (some studies suggest a possible ancestry from helcionelloids, but the relationship is controversial) and all known species are still entirely endemic to the corpse-isle. Crown-group xenotherians likely appeared much more recently, which most evidence suggesting the most recent common ancestor of all living species evolving during the Early Mesozoic. Since then, they've adapted to the changing conditions down vaguely analogous lines as vertebrates, although anatomical differences are vast between the two groups.

Ancestral xenotherians have six legs, although one or more pairs have been modified, reduced, or entirely lost in some species. The eyes are mounted on muscular turrets, giving most species a very wide range of sight, and nearly all xenotherians are primarily vision-based navigators. Most xenotherians tend to be vividly coloured and patterned and many have the ability to change their skin pigments, although the degree of this ability's complexity varies from species to species. Their skeletons are comprised of a chitin and calcium carbonate composite, while the hair-like filaments which cover their body are evolved from the protein conchiolin fibres found from on the mantles of many molluscs. To assist in navigation and orientation of three pairs of legs, two secondary ganglion masses occur in the middle and posterior body portions which assist in controlling autonomous functions of the lower body. The face consists of six muscular palps, which in some species have been modified into horns or prehensile tentacles, or fused together. Their blood is a milky magenta or light purple when oxygenated due to being comprised of a protein matrix of hemerythrin and hemocyanin, which is pumped through the body by an anterior and posterior heart.

Over some two-hundred or so million years, the first xenotherians evolved into dozens of species of widely varying forms and lifestyles, from vicious fang-mawed hunters, bizarre tall-bodied browsers, worm-like burrowers, herd-dwelling grazers, winged scavengers, rat-like creatures weighing only a few grams to hulking beasts over one ton, and everything in between.

---

MAJOR GROUPS OF XENOTHERIANS*

TEDDIES: The basalmost group of living xenotherians, and likely represent what the original ancestors of all modern species descended from. Distinguished by six walking legs of equal length and a sprawling reptilian posture. All species retain four claws on each foot, resulting in a zygodactyl foot arrangement, have a thick hairy coat, and reproduce through oviparity. All species are predaceous, but have a moderately generalist diet. Because of their thick coat, their colour-changing abilities are limited. Group represented by the grizzly teddy.

SQUID MONKEYS: A group of primarily arboreal, six-legged xenotherians, with degeneration of the mid-ganglia allowing for a more flexible body. The front pairs of palps have been elongated to tentacle-like grasping organs, while the bones inside the two front pairs of walking appendages have greatly degenerated for greater agility while moving arboreally, sacrificing ground mobility. All species are excellent climbers and adapted for vertical environments. They retain all four claws, allowing them to grasp branches, cliffs, and vines easily. The range of movement among them is the most varied of any xenotherian group, with species capable of hexapodal, quadrupedal, and some even very limited biped motion. Group represented by the thogg.

URCHIN-HOGS: Hexapodal xenotherians that are primarily pseudo-herbivorous, they are so named for their spiny coats of bristling spines, which can anywhere from subtly hardened hair to a vibrant coat of huge quills and curved bony spikes. In some species, these are enhanced by toxic secretions, while others rely on the durability of hardened spiky armour derived from the hairs. The tongues have been adapted into radula-like grinding organs used for chewing and can no longer project from the mouth, and so the lower pair of palps have been adapted into prehensile graspers to compensate. These are egg-layers, although some retain the eggs inside their body until they hatch; all species produce infertile eggs to feed their young. Group represented by the burr boar.

DRAGONWINGS: A clade that has evolved powered flight, with skin-membrane wings derived from their front and middle limbs, and an exceptionally large and complex lung cavity to take in oxygen. In the ancestral species, there was a thin tail to balance, which has been lost in many species. In some species the two pairs of wings have become fused into a single pair of wings. The last pair of legs retain four-claws, while the mouthparts have been heavily altered in numerous lineages to reduce weight to the head; however, some are flightless. Smaller species tend to be bipedal, although larger species may bear some weight on the wings on all sixes as well. Group represented by the skincrow.

STRIDERS: One of the most morphologically distinct subgroups of xenotherians, these are specialized browsers which have evolved extremely elongated upper bodies, creating a roughly humanoid, upright form that still walks on four legs (with the front pair of limbs used as manipulator arms). The tongues of the striders have become elongated, muscular appendages used for manipulation similar the trunk of an elephant with the arms and legs so far from the head, with enlarged storage sacs in the upper "chest" behind the face where they are kept at rest. Most species have some type of fleshy lobes over their upper body which are used for display. Group represented by the star strider.

BLISTER-BEASTS: Quadruped xenotherians that are primarily pseudo-herbivores, in the group one or more pairs of palps, as well as the front appendages in some species, have been adapted into horn-like structures used for display and/or defence, with a variety of fantastic ornamentations. They are named for special glands on parts of their body (the location of which varies from species to species) that allow them to shoot potent vesicant compounds for defence. Their more compact bodies compared to urchin-hogs allows them to run faster but sacrifices agility. They grow a type of fatty, nutrient-rich tissue on their undersides when rearing young as food for them. Group represented by the black cattle.

WRATHRATS: Sometimes considered to be the corpse-isle’s equivalent to rodents, this is a grossly oversimplified, if not entirely inaccurate description. Their name comes from their relatively small size and ever-growing hard beak at the front of their palps (functioning analogously to a rodent’s incisors), although neither attribute is universal. Although closely related to the grazing blister-beasts and more distantly related to the browsing striders, these are mostly predaceous and many are notoriously vicious hunters. All members are quadrupedal, with the front pair of limbs modified into grasping appendages. Group represented by the banshee.

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*Branches designated with a plural have several members; those that are singular only have just one or two species total, representing only minor, but still notable offshoots.