All centiverms and hexaverms have complex nervous, digestive, circulatory, respiratory, excretory, and reproductive systems. Depending on species these systems may look different or have slightly different functions but this Centaur can be used as a general baseline, at least for hexaverms.

The tetraverm respiratory system occurs in the form of one large lung-like organ connected to two nasal openings. The channel leading to the lung is filled with chambers separated by muscular trapdoors that can open and close to create different sounds. When relaxed, the back of a hexaverm's neck moves up and down slightly when it breathes.

The closed circulatory system of tetraverms is advanced and sufficient for supporting mega-fauna, much like Earth vertebrates. Their blood uses hemoglobin pigment and is fueled by a large dorsal tube heart, comparable to Earth arthropods though far more efficient. Typically tetraverms are mesothermic, warming certain parts of the body like the brain or legs when more active. Some may be cold-blooded or warm-blooded depending on what is advantageous in their environment. Active predators such as centaurs, sprites, and some centiverms are usually warm-blooded while smaller terrestrial hexaverms and centiverms in hotter environments are usually cold-blooded.

Tetraverms have a unique digestive system. Most retain the nemertean rhynocoel, a pocket that contains a hydrostatic proboscis with a venomous stylet used for incapacitating prey. Larger species with raptorial means of dismembering prey or an herbivorous diet usually have a greatly reduced rhynocoel though it may still be used to secrete digestive fluids or taste. Ahead of that is the large pharynx that contains several rings of sharp or blunt teeth depending on diet. Aquatic species can use a rapid opening and closing of the pharynx to achieve suction of prey. Beyond that, the carnivorous tetraverm digestive system is straight forward, containing an esophagus, stomach, intestines, and anus. Herbivorous species usually have multiple stomachs in order to break down plant fibers.

The excretory system of tetraverms is odd, containing two organs that serve the function of a bladder and kidneys. This chambered organ contains several chambers filled with different amounts and mixtures of waste material, emptied once they become too full. If one bladder chamber were to become damaged or infected, other bladders can fill its purpose though not as efficiently. This odd system of checks and balances was mainly developed in the tetraverms' aquatic ancestors due to their need for ammonium for buoyancy. Some terrestrial species can still produce large amounts of certain chemicals from the kidney/bladder organ to secrete noxious smells or toxic flesh.

While the tetraverm nervous system is advanced, it isn't particularly special in the animal kingdom. Most mesothermic and warm-blooded species have an intelligence comparable to Earth avians, being able to solve problems and communicate with a variety of sounds and displays with meanings. The brain of tetraverms is connected to two lateral nerve cords running through two spines, the basis of their skeletal system and main support of the limbs. While the olfactory, tasting, and seeing senses of most tetraverms are well-developed, their hearing is less so. Most will have multiple "ears" on the dorsal side of the body in the form of vibration sensing antennae and pits beneath them which trap and register sound waves.

Finally, the reproductive system of tetraverms. Like the nervous system of these animals it is also not very interesting. Both sexes have a cloaca on each side of the posterior. Their nemertean ancestors reproduced by broadcast spawning gametes through out many lateral holes on the body. Now the tetraverms use more efficient internal fertilization via a cloacal kiss, again in a similar manner to Earth avians. Once the female's eggs are fertilized she will either lay hard shelled eggs or give live birth depending on species.

Like Earth vertebrates, tetraverms have an endoskeleton for support and organ protection. Beyond that there are few similarities. Though tetraverms have developed structures akin to ribs, these spinal protrusions are immobile and arise in both directions vertically. The ventral ribs are far shorter due to the spine being closer to the bottom of body and having less organs to protect. The dorsal ribs are far longer due to major organs like the heart and respiratory system being on the back rather than the chest. Also unlike vertebrates, the tetraverms have no set amount of spinal segments. While the centiverms can have dozens of vertebrae in their necks and bodies, hexaverms typically only carry a few in each. Between the neck and body is a joint that limits upward and sideways movement for rigidity. The legs of tetraverms always have seven parts, named according to arthropod naming schemes. The first segment is almost always internal and not visible. Instead of vertebrate jaws, the tetraverms use tentacles to grasp food and thousands of teeth arranged in rings to masticate it.