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Forest Gulper - A large creature that lures creatures into its mouth by scent, then slowly digests them alive. They resemble a gigantic green barrel with a thick snake-like tail, and a pair of atrophied beating wings. These wings are used for flight in the Gulper's larval stage, but become vestigial as the animal matures. 

Forest Slider - Forest Sliders are bipedal animals that are born with four limbs, but as their rear skid hardens and matures, their hind limbs shrivel and eventually fall off.

Gelsucker - The Gelsucker is a quadruped, but also has a pair of clawed arms, giving it a total of six limbs. Gelsuckers are so called because they feast on the flesh of the Jelly Bladder plant, which grows in small groves on the outskirts of pocket forests. They use their clawed arms to rip the Jelly Bladders open, and then use their extendable proboscis to suck out the semi-solid flesh.

Gill-Head - A biped with a spike on its chest to support it, almost like a third leg. They are one of the last remaining terrestrial air-sifters, such as the Rime-Runner. The Eosapien prey upon it.

Groveback - In Alien Planet the Groveback is one of the largest creatures native to Darwin IV. When fully mature, they are large enough to have entire stands of trees grow on their backs during the long periods of dormancy spent buried in the ground. Once mobile, they travel on two large front legs and a rear appendage shaped much like a boat rudder. The feeding habits of the Groveback differ between the book and the film. In Alien Planet, the Groveback feeds by absorbing nutrients from the soil through the skin of its underbody. In the Expedition, the Groveback is a filter feeder, feeding on the microscopic plants and animals that number in the millions in Darwin IV's air currents. Considering the Groveback's size and speed, the first mentioned lifestyle may sound more realistic, but when considering the multitude of slow filter feeders and a many nostril-like orifices covering the Groveback's head, the latter lifestyle is just as possible. 

Gyrosprinter - The "antelope" of Darwin IV. However, unlike the antelopes of Earth, the Gyrosprinter has just two legs arranged in a rather unconventional manner - one right behind the other. The legs appear to have evolved to become fused from two forelegs and two hind legs over millions of years; the Gyrosprinter's ancestors were probably once quadrupeds like Earth's quadrupeds. Unfortunately, such a placement of legs can be a problem for balance. The Gyrosprinter has solved this by having two balance organs (similar to the inner ear of a human) located in two thick prongs protruding from either side of its body. It has two hearts, a two meter long tongue, and its nostrils are located on its shoulders. The Gyrosprinter is able to out run its predator (the Arrowtongue).

Hook-tailed Flyer - A yellow, medium-sized flyer with a hooked tail and a single float bladder.

Ice Crawler - Quadrupeds that resemble pillbugs are nearly motionless and make comically flatulent noises when emerging from their "sleep sack".

Ice Dart - A small flying animal that has three pointed tubes for feeding and drinking, one on its face, another on its bottom sides, and a third one on its rear. It also pokes itself on ice during snow storms.

 Jetdarter - One of Darwin IV's more bizarre aerial life forms. The Jetdarter is a scavenger whose compact body assumes a dart-like shape. It has no wings to aid in flight. Instead, it has a biological version of a ramjet engine - complete with a turbine of bone and gristle. It has two legs which fold up during flight, although on Alien Planet, they do not appear to have legs at all. The Jetdarter forms nests in the pocket-forests and fears many predators, such as Electrophyte plants and Finned Snappers.

Keeled Slider - The Keeled Slider is a large brown animal with kneeled arms. It builds special egg chambers to keep eggs and young. It slides down muddy mountains. It is not hermaphroditic.

Littoralope - The Littoralope are the creatures that use huge Sea-Strider skulls for shelter in Expedition. In Alien Planet, the Littoralopes are described as placid, slow-moving quadrupeds with little evidence of intelligence. They also have tails resembling their heads, similar to Symets, which did not appear in Alien Planet. This feature probably evolved to confuse predators.

Mummy-nest Flyer - They are black flyers, with a tail that bends back to meet the front of the body (like scorpions, except the tail is curled under the body, not above). Unlike some flyers, they are not jet propelled, so they have to flap their wings to fly.

Mummy-nest - This animal has sphincter-like orifices on its body. It is later invaded by Mummy-nest Flyers (though they may have once been one and the same). 

Prairie-ram - Prairie-rams are ubiquitous liquivores that impale their prey's chest to suck out bodily juices.

Prismalope - A triped of Darwin's plains, Prismalopes often travel in herds. The first thing one notices about this creature is its massive prism-shaped head. Though it appears ungainly, it houses the Prismalope's grasping tentacles, which it uses to capture small prey. This fast-breeding creature is preyed upon by a multitude of predators, both terrestrial and airborne. The Prismalope hunts a flyer that is "protected" by the Butchertree.

Prongheads - Prongheads are bipedal predators that feed on Gyrosprinters and Littoralopes. They are named for the three hollow prongs protruding from their faces that act as tubes to siphon liquids from their prey, since they use their feet to inject their digestive fluids into prey. They hunt in pack in a similar manner to wolves on Earth.

Rayback - An agile and aggressive predator of Darwin IV's grasslands. This creature gets its name for the four tall ridges that project from its back. Apart from its ridges, the Rayback does not appear to have any specialized features. Its only weapons are its lightning-fast speed and a dagger-like tongue. It is fierce and attacks anything that moves. It was the first animal encountered by Barlowe, and apparently, his sudden appearance caused it to start attacking him and his vehicle. A biped, it bears a general resemblance to the Bolt-Tongue and Arrowtongue.

Rimerunner - The Rimerunner is a one-legged animal from the polar regions of Darwin IV.

Supported by only one leg, the Rimerunner hops across its Arctic home like a kangaroo. It eats only aerophytes and other microscopic airborne organisms. At the front of its head, the Rimerunner sports an umbrella-like organ. This organ, suspended by thin neural cables, is a sophisticated sonar system along with a simple and atrophying eye.

Rugose Floater - Rugose Floaters are heavily wrinkled, fish-like aliens that float in the air. During spawning season, they have eggs trailing behind their "fins" and reduce to their crescent shape when spawning is complete. This is the creature seen on the front cover of Expedition.

Sac-back - The Sac-back lives at the edge of the Amoebic Sea. The Sac-back gets its name from the sac on the male's back. The sac is used to store pre-digested food from the "sea", which is later fed to the females. Male and female Sac-backs live completely different lives. Males live on the surface, walking around on their three legs. Female Sac-backs dig "tombs" in which they bury themselves. Once buried, the only part of the female that sees the light of day is her mouth and tentacle.

Scavengewing - Scavengewings are flying animals that have a special digestive system suitable for eating carcasses.

Skewer- The largest aerial predator of Darwin IV. It is an enormous flying creature, with a wingspan of 50 feet (over 15 m). Not even the largest pterosaurs (like Quetzalcoatlus, with its 40-foot wingspan) from Earth have a wingspan even approaching that size. Its wings do not flap but squeeze, shifting shape to shift flight. It is actually propelled by combusting methane gas in four jet-pods on its wings. This allows the Skewer to travel at speeds of 200 miles per hour. Its killing tool is a hollow lance that impales its prey, injects digestive enzymes, and sucks the corpse dry. The Skewer also hunt in groups, each Skewer dropping the spoils and another swoops in to feast.

Spade-nose - A quadruped that lives in forests and has a blue spade-like nose, hence the name. It is a common prey of the Gulper.

Springwing - The Springwing is a winged animal with forelimbs somewhat like those of a horse's. The appearance of a Springwing is similar to that of a mountain goat. It springs itself off cliffs, gliding with the alpine updrafts to reach its destination.

Stripewing - The Stripewing is a lazy flying creature with stripes on its wings which breaks into a hopping frenzy each night. Stripewings will fold themselves into compact shapes. They can often be seen, massive colonies, sleeping on the surface of the Amoebic Sea.

Symet - Symets are herbivores named for their protective symmetry. In Expedition, Barlowe observes a herd of Symets in a desert in bordering the Vallis Przewalski. The symmetry may have evolved to confuse predators.

Thornback - The Thornback is an herbivore that walks on its three-legged gait. It has a large "thorn" on its back shaped like a shark fin. Its head vaguely resembles that of a rhino's.

Trunksucker - The Trunksucker is a small animal that glides through Darwin IV's forests and clings to Plaque Bark Trees, sucking their sap. The first dead creature that the probes find on Darwin IV is in fact a Trunksucker, most likely killed by a Daggerwrist.

Tundraplow - An animal that digs part of its body in the ground. It gets food from its underground proboscis, pulling plants from underneath.