Possibly the biggest exobiology project in history, Sagan 4 is the joint creation of many users. Anyone can add another species by picking a previously existing species (alive in the current generation) and “evolving” it into something new. This has led to an explosion of biodiversity on the planet. As of 2021, there were 41 kingdoms. Learn more at Sagan4.org and forum.Sagan4.org

A selection of drawings from Sagan 4 can also be seen here: disgustedorite

Or, as informed by the commenter below, here: hydromancerx

Reccembra is the creation of DeviantArt user Earlegs. It is a roughly Earth-like planet with the equivalent of prokaryotes and eukaryotes, algae, chemotroph fungi, and simple animals with some very strange embryology.

Aderrica is a world of sea-dwellers with six fins and land-dwellers with six legs. There are flyers, climbers, burrowers, grazers, and predators. There are those that lick up detritus and those that snap their oversized jaws around prey.

There are many seed world concepts in speculative biology projects. Serina is a world populated by guppies and canaries introduced from Earth. Kaimere is populated by many Earth lineages introduced over long periods of time. Much more exotic, the Mammalian Ectoparasite Seed World (MESW) by Twisting Depths is a world of ticks, mites, fleas, flies, and lice. Some have grown to monster sizes and include cuddly blade-faced predators, grass-eaters, and shark-like organisms. Check them out.

Katie is the creator of four worlds: Xenosulia, Amthalassa, Nemoros, and Eurus. Each has its own blog out in the internet wilderness (Amthalassa shares its blog with stories of a British garden). The posts are in the order of most recent articles on the top, so you’ll want to go to the bottom to read about the climate, biochemistry, and anatomy of the major clades. Later posts cover specific biomes and genera.

Amthalassa is a world of ammonia, methane, and hydrogen. In deserts, moss fixes its own nitrogen to create ammonia to keep from drying out. Soft-stemmed kelp-like “trees” fill their bladders with hydrogen to support their weight in the thick atmosphere. Smaller plants crawl very slowly from place to place. Animals are radially symmetrical, with one eye per leg, a ventral mouth, and a dorsal tail containing an anus and genitals. Many are saucer-shaped. Others are snake-like with their legs clustered around the mouth. Still others have become bilaterally symmetrical, but retaining one eye per leg. There are herbivores and carnivores. There are shells, spines, and feathers. There are floating grazers that hold symbiotic, hydrogen-containing plants. There are eyes with inner and outer lenses able to move relative to each other. It’s a beautiful place.

Xenosulia is a tidally-locked world of acid rain and air algae. Trees are bilaterally symmetrical to better face the unmoving sun. Land animals sift algae from the air with the equivalent of baleen. Others are predators or grazers. The dominant animals are descended from radially symmetrical ancestors, with mouth and genitals on top surrounded by a compound eye ring and the anus on the bottom at the end of a tail. In most lineages, there are two front limbs and the anal tail has become a third limb for hopping. Skeletons are silica, nerves operate on triggered bioluminescence, muscle cells shrink by bonding gas from bubbles into specialized proteins, and many animals carry their haploid offspring as symbiotes. Wings are supported by blood vessels, spines provide thermoregulation (and more), and jaws evolved several times in different ways. The biodiversity is filled-out, with vaguely sloth-like, turtle-like, snake-like, mole-like, scorpion-like, and dromaeosaur-like forms. Another interesting lineage with potential is the “hingeflies.”

Nemoros is a moon of planet Aulea. It is a world of ammonia volcanos and very cold temperatures. Methane lakes dot the icy soil. Grass-like and tree-like producers cover the landscape. The nitrogen atmosphere is thick, allowing animals to tumble along with little effort. Those with hydrogen bladders can easily swim/fly. The atmosphere is also very hazy. Chemosynthesis is more common than photosynthesis. Sonar is more common than sight. Plants take in methane and store their food as acetylene. Animals eat the plants, inhale hydrogen, and exhale methane. The dominant clade is one of tetrahedral symmetry, though most lineages have evolved various forms of radial or bilateral symmetry. The animals flower, producing larvae that fuse in pairs to produce chimerical adults. Limbs move by the opposition of contracting muscles and expanding muscles.

Eurus is a low-oxygen world with an axial tilt of 87 degrees. The winds are severe. The plants resemble bamboo. The land animals are descended from molluscoids and have their anuses near their mouths. Their muscles exist inside hollow bones. Making use of bioluminescence, their nerves operate like those on Xenosulia. There are turtle-like and ferret-like forms. Smaller relatives with more legs also have wings derived from fins.

DeviantArt user Concavenator writes about the planet Ea. Unlike most projects that focus on one ecosystem, this project gets into the interactions of organisms with partly incompatible biochemistries. After several decades of environmental and political turmoil on Earth, humans have moved to Ea to repeat their mistakes – and they’ve brought their cats with them.

Few projects go into as much depth as this one, covering plant reproduction, cellular structure, biochemistry, and so much more. As of this writing, it still only has a few lineages though, including descendants of starfish-like animals, some who have converted one arm into a head, leaving four limbs left over, and some who have merged two arms into a head, leaving three limbs left over. It’s great!

Isla is the creation of DeviantArt user bionautic (also on Instragram and YouTube). It is a tidally-locked world where life lives only near the “twilight zone” between the cold night side and the hot day side. Plants are often flat to deal with the constant wind in this area, though some rise above the surface somewhat to better capture the very horizontal sunlight.

Though lower in biodiversity than Earth, there are several interesting bidirectional animals described, as well as some of the variety in spore dispersal used by the plants.

Isla is also a world I can feel at home in while it captures the imagination. It has many cozy nooks and crannies created by the plants, whether it is the gaps between the generational reefs of flat desert plants, the root mesh underneath large plant colonies, or the world under the solid canopies of the “spore forests.”

Although I have seen many equally-good artists, this is the best art I have seen that was coupled with clear biological prose into a real project.

One of the most imaginative projects I’ve seen in a long time, planet Polinices created by DeviantArt user doublejota is dedicated to the question of how far we can take the concept of a colonial organism. There are worms that bud smaller versions of themselves from within their stomachs, who in turn bud more. Some colonies remain wormlike while others branch and house symbiotic algae. Some colonies are circular and roll like tank treads while others are donutlike and lined with needlelike teeth on the inner surface.

Some colonies have three members that resemble a fish and two large pectoral fins. They can move by fins or by siphons. Some colonies have two main members that face opposite directions and resemble Earth fish except for the four eyes in the middle of the body (derived from the gastric sacs of smaller members). Some colonies grow a long tubular shell that curves back and forth and some of these resemble fish in overall appearance with the propulsion tail member surrounded in two dimensions by serpentine shell.

In some colonies, the members detach and cooperate in ways reminiscent of a beehive. Forager drones gather food and bring it to the queen for digestion. Some swim. Some crawl. They communicate by radio and require repeater drones due to the limited range of radio waves in water. There are many variations on this theme, including the drones lining up as in a buffet, drones stringing together in chains while they filter-feed and are passed through the queen, and queens without drones that mimic radio calls to lure in the drones of others as prey.

There are also members that fully detach and roam in packs. Only some can digest, some can capture prey, and some can reproduce. It’s an extreme form of caste system similar to something I thought up once.

Furthermore, I also enjoy the variety within the variety. Some colonies have eyes on each end, but in some of those colonies the lenses of the eyes have overgrown into giant shells that the colony can pull together to cover itself. There are many kinds of shells and in some colonies the two shells can have different shapes and sizes. A lot of thought has gone into this project. I have barely scratched the surface in covering it and have left quite a lot unsaid.

The art is great and includes a mixture of diagrams and landscapes. Many of the animals are multicolored with sharp contrasts like tropical reef fish on Earth. It sets up a feeling that’s enough to just immerse yourself in after a long day. Fortunately, there is talk of a future book.

​Kalagari is the creation of YouTube user Ben Pebbles. It is a planet of purple plants with swimming fruits. There are also animals and green plants. I enjoy watching the animations of the seal-like and buffalo-like creatures. The narration style is humorous and tends to jump from one organism to the other by their ecological relationships. Watch the videos here.

Project Rose includes not just one, but three planets, Nusku, Mazu, and Ullr, all within the habitable zone of a red dwarf star. Nusku is tidally locked, giving it a permanent typhoon where it faces the sun, surrounded by desert, surrounded by temperate forest, surrounded by ice near the windy twilight zone. The “night” side of the planet is dead. Mazu is a water world with little or no dry land. Ullr is like a colder, larger version of Earth.

​As of this writing, only Nusku life has been described and plants are just beginning to move onto land. They resemble purple mushrooms, ferns, or palms. There are two basic lineages of animals: Filter-feeding, radially-symmetrical animals evolved into bilaterally-symmetrical fish-like creatures, some with armor and some with jaws. Flat animals with four mouths and one anus evolved into burrowing, swimming, and barnacle-like forms, some with parapodia, shells, hair, backbones, beaks, hooked tentacles, “swords,” or “saws.” Some filter the water with all four mouths. Others bring water in two of the mouths, filter it for plankton, and expel it out the other two.

Watch the ongoing saga on YouTube.

The planet Almaishah is the creation of YouTube user Dapper Dino and its inhabitants are the collaborative effort of many speccers and artists. Every few months, the project enters a new phase, setting the clock forward ten million years and causing extinctions. New plants and animals are added, but must derive only from those species already in existence. Because it is a collaborative effort, there is some variety in the art style and the length and detail of the descriptions read aloud by Dapper Dino. The large-scale groupings of organisms are more diverse when everyone is trying to take things in different directions. Some focus on behavior, others internal anatomy, others external anatomy.

As of this writing, phase three has just ended. Life still lives primarily in the oceans, but a few animals have adapted to taking short strolls above the tide line. The biodiversity is exciting. The art is professional.

There are boneless tetrapods, some resembling tiny horses or crocodiles, jellyfish-equivalents taking the roles of limpets, leaches, and corals, echinoderm-equivalents sometimes taking the roles of jellyfish, and segmented animals already diversified into forms vaguely reminiscent of fish, turtles, earthworms, shrimp, spiders, beetles, lobsters, swimming centipedes, and giant, blind, heavily-armored worms that slither along the bottom and eat whatever is stupid enough to stumble into their oral tentacles. There are purple plants filling the roles of seaweed, true plants, and corals. There are animal-like swimming green plants, some of which have lost their chlorophyll and become red plankton, and some of which have lost photosynthesis entirely and become vermiform detritivores. There are also animal-like radiotrophs that feed on the energy from radioisotopes, some of which have also developed photosynthesis and chemosynthesis. I don’t understand their anatomy at all.
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Watch the ongoing saga on YouTube.

YouTube user Biblaridion, who normally covers language creation in world-building, has also created a playlist of videos featuring the step-by-step evolution of life on an unnamed, Earth-like world rich in hydrogen sulfide. The graphics are great. The concepts are plausible. Watch it here.

Preradkor is the creator of not one, but two worlds, planet Coatlique and planet Ullr. Coatlique is home to large animals reminding me simultaneously of mammals and arachnids, although some resemble sharks with whip-like jaws. Coatlique is hot, stormy, and irradiated, leading to a high level of mutation such that all animals and plants are chimeras. Ullr is much colder. It is home to the askewbugs, asymmetrical insectoid organisms. Check out his DeviantArt gallery.

Illuria is the name of a planet with its own wiki that anyone can edit. According to the introduction, it was discovered in 3018, has a 48-hour day, and a year that is 730 Earth-days long.

In addition to mountains, deserts, scrublands, savannahs, temperate forests, rainforests, marshes, and prairies, it has acid swamps and the “mineral sea,” a body of water rich in iron, gold, and silver. Its sub-biomes include rust reefs, crystal caves, and wiregrass meadows.

Among the animals of Illuria are crystal borers, shrimp-like, colonial animals that make nests out of crystals.

Among the plants of Illuria are crawling boom creepers, plants that grow rapidly at night on stored fuel, seeking out sleeping animals to infect with its spores, which it often delivers so explosively that the animal is killed.

As of this writing, the ecosystem is still incomplete. The life on the continents is undescribed. The gold shiners eat shellfish that have no page of their own. The hovizards lay their eggs on stilt plants with no page of their own. Visit and add your own ideas.

​There are many awesome artists on DeviantArt.com, but not all of them have well-defined exobiology projects. Some focus on the behaviors and outside appearance of long-extinct organisms on Earth. Some engage in all kinds of art and mix all their work together. Some post great alien pictures, but give no descriptions or environmental context. Some deal more in fantasy than science fiction. Some only had a few good ideas and then stopped. Some create strange landscapes covered in what might possibly be plants perhaps inspiring someone else to offer design and explanation. Here are those that at least deserve recognition as artists:

Demmmmy is the creator of Fentil, an Earth-like planet of higher gravity and thicker air. It is the flora of planet Fentil I am most enamored with. There are plants that grow at the top, creating gigantic basket-like structures. There are plants that breathe. There is good fauna, too. There are the complex skeletons of the Dystroma and the complex vascular systems of the Photonimals. They are both highly creative and surprisingly plausible.

​Salpfish1 is the creator of several worlds, including Tregama, home of swimming creatures with siphon-legs and the charybdis fish, which uses suction to create whirlpools and feed on anything on the water’s surface. He also creates a variety of future Earth animals, such as land anomalocarids, fish-like mollusks that eat anemones and then spit stinging cells at predators, and pigs that hunt like frogs. Another favorite of mine is the blind, flying, cave shrimp.

Concavenator is the creator of Horus, a world connected to Victorian-era Earth via wormhole. It is home to red plants with hearts, tube-jet fish, and large land vertebrates. The animals have a double spine. The dorsal spine runs from the skull along the back, while the ventral spine runs from the chest along the tail. They are connected by ribs. The tail houses the respiratory and sometimes reproductive organs. The land animals have six limbs. Some run on the hind limbs and use the forward limbs for grasping while the middle limbs are vestigial. Others stand on the front limbs while the rear four are used as wings. My favorite is the lazy animal that uses its front limbs to carry its head around while it grazes.

​Tapejara is the creator of not one, but six worlds, including Tunjera, Adam, Eve, Lyell-3, Toci-1, and Midgard. They are currently all unfinished but all have huge potential. The animals are very creative. Planet Adam is home to “fish” with large ventral “mouth-bodies” attached only by a narrow tube containing the esophagus. Planet Eve is home to completely armored creatures whose only openings (the mouth and anus) are both located in the head. Some are colonial. Toci-1 is home to animals with chain-link ribcages, helical muscles, and specialized organs capable of regenerating any damaged tissue anywhere in the body – as if all the stem cells were in one place.

Abiogenisis is a mind-blowingly good artist in general but especially of alien sea life. My favorites are the swordswallower, bushwacker, cloakmouth, and antlerworm. I hope these eventually get organized together in an Expedition-style book someday.

Avancna is the creator of planet Tlaquanaru. Although the map proves it is certainly not Earth, the animals are eerily similar to those of our world. There are what appear to be descendants of iguanas, birds, moths, and very many fish. My favorites are the rolling echinoderms and the rotifer-cephalopod-creatures that drop pom-poms full of ammonia to deter predators.

​Ramul is the creator of Red Earth, a planet about halfway between Earth and Mars in all its characteristics. It is home to a staggering number of octopod species, but my favorites are the worm grasses (plant-like animals), siltribbons (worms with long mouths that suck up muck), monolingulates (filter-feeding squid-things), and the era worms, which are known to hatch all at once and secrete a poison that kills everything around them.

Biofauna25 is the creator of not one, but two worlds, Epimethius and Odin. Either project has the potential to be a great book.

Epimethius is a larger, stormier version of Earth. There are at least four lineages of plants, including the ridge-leaves, the maze-roots, the feather plants, and the peeling plants. There are an incredible variety of radially-symmetrical animals, some resembling insects, crustaceans, mollusks, amphibians, and mammals. Variations on the theme include laterally flattened shrimp-like forms (making them bilaterally symmetrical) with their eyes on the back end. There are even more bilaterally-symmetrical animals. They have dual ribcages. The ventral ribs house the digestive organs and the dorsal ribs house the heart and respiratory organs. Many resemble fish and snakes. Others resemble deer or crocodiles. Some make silk, some retract their heads into hoods, and others have their simple mouths in the chest. My favorites are probably the frog-like potes.

Odin is a small, relatively dry planet largely covered by inedible sheddings of red plants floating in the air. Different species of floating plants receive energy from sunlight, lightning, or wind motion. They form wide nets to safely diffuse electrical discharges. There are three main groups of animals. The first has a four-stage life cycle, the second has a five-stage life cycle including a sessile phase that feeds the young with nectar, and the third has a five-stage life cycle like the others, but in reverse. I don’t know exactly how he organizes them into groups, but I estimate there must be at least twenty-seven orders.

Juniorwoodchuck is the creator of Aurora, planet with long days and animals which spend one life stage as a plant. He also speculates about future Earth life, my favorite examples of which are the turtles that swim with their necks and the squid-moles.

​Snaiad is an exobiology project created by C. M. Koseman. The planet Snaiad is inhabited by many creatures, of which the vertebrate phyla are described on the website. These animals have hydrocarbon bones, hydraulic muscles, endocrine-based cognition (as opposed to neural), and two heads. The lower heads are mostly boneless and used for eating. The upper heads are actually heavily modified genitals used for defense and covered in sensory organs. There has been talk of turning it all into a book. I really hope this happens, but only if the invertebrates, plants, and microbes are also described.

Planet Epona is a dying world with only periodic volcanism. It is during these short bursts of ten million years or less that life flourishes and diversifies. Otherwise, it survives only in the seas where it can barely scrounge up enough carbon to grow. There are several lineages of plant and animal life, including bubbleweed, tiered seaweeds, pentapods, bivalve ambush predators, and colonial flying insectoids. The pentapods and tiered land plants make use of bone-muscles that expand rather than contract. They have variable metabolisms based on interesting biochemistry. While the project seems to have stalled, it can always be revived and in any case is worth the read.