Anatomy of Hex Thraxes

Thoracostomes (thraxes for short) are among the most successful land animals on Ilion. 92% of detritivores and 60% of primary consumers belong to the group, owing to their versatile design and rapid rate of reproduction, among other things. They are named for the placement of their mouth, which is not in the front as in other red plant derivatives, but on the chest between the front pair of limbs. The mouth, which is filled with tiny scraping teeth, lies flat against the ground. Since this arrangement is not conducive to breathing, oxygen and carbon dioxide must diffuse across the skin. As a result, thoracostomes adapt well to an amphibious or aquatic lifestyle in freshwater and ocean habitats.

Phylogeny of Thoracostomes


Hexapede thoracostomes – A single mutation caused all of the ancestor’s offspring to develop only six out of fourteen legs. Amazingly, this deformity did not affect organ function and the lineage grew into one of the most adaptable animal groups on the planet. Due to their ability to concentrate toxins, microbes, and pigments in their skin, some species can be quite colorful.


Tube-footed thraxes – Members of this group share many similarities to their sister clade but with longer bodies. Most tube-footed thraxes rely on concentrated toxins and warning coloration to make themselves unappetizing to predators, while others get by with camouflage. Some species have a special stomach compartment for fermenting black plant microphylls, which are normally too difficult to digest through conventional means.


Microthraxes – Measuring in the millimeters, microthraxes play an important role returning nutrients to the soil. They are found in leaf litter, fur, and decaying organisms, feeding exclusively on dead material. Their eyestalks, while still functional as sensory organs, serve mainly to manipulate food.


Clawed thraxes – Like the name indicates, these animals have claws on their feet for clinging to trunks and branches. Their jointed, dexterous eyestalks are perfect for seeking out higher quality food sources such as red plant fruit buds and small animals.


Stack-eyed thraxes – While most thraxes have rudimentary vision, their visual acuity is poor. Stack-eyed thraxes evolved to secrete a substance into their heat pits that hardens into a lens. The lens only lasts a limited amount of time before it becomes too cloudy to see through and must be shed on a regular basis. The photoreceptors fall out with it and a new eye and lens erupts from below, much like shark’s teeth.


Assorted Hex Thraxes

Hexapede Thoracostomes numbered1. Ventral view of a typical hex thrax. Six suction pad feet and a radula lie flat against the chest.

2. Obsidian thrax and two unnamed species adapted to freshwater environments.

3. Five brachyderm thraxes. Branched and feathery extensions of the skin aid in thermoregulation, gas exchange, and camouflage.

4. Cobalt thrax, an ectoparasite

5. Tiger’s toe, a detritivore

6. Heart of gold, an herbivore

7. Dogskull, a scavenger

8. Ax thrax, a shrubland herbivore

9. False buoyphyte, one of the many surface grazers of Hidden Lake

10. Planted pot (a red plant) and its mimic, the faux pot.

11. The berries of the black plant on the right are a dietary staple of many herbivores. The prominent structures on the imitator’s stalk are filled with eggs. The male cements the egg sacs onto the female’s stalks and fertilizes them before wandering off in search of another mate. When eaten, the larvae hatch and parasitize the host until they reach breeding age.

More assorted hex thraxes

More assorted hex thraxes

West Deiphobus darkstar

West Deiphobus darkstar

Persian rug thrax

Persian rug thrax

Bald man thrax

Bald man thrax

Two-spotted stinger thrax

Two-spotted stinger thrax

Yellow ridged thrax

Yellow ridged thrax

Red cell thrax

Red cell thrax

Irridescent stinger thrax

Irridescent stinger thrax



Greater false archer

Greater false archer

Gray ridged thrax

Gray ridged thrax

Hedgehog thrax

Hedgehog thrax

Fan Thrax

Fan ThraxThe fan thrax is a typical hexapede thoracostome, displaying the usual six suction-cup feet, two infrared-sensitive eyestalks, and a ventral mouth. The sail aids in thermoregulation and gas exchange. The boils are filled with a foul-smelling pus to discourage predation.

Rock Thrax

Rock Thrax

The rock thrax lacks chemical defenses and depends instead on camouflage to avoid detection. The animal and its relatives scrape lichen-like plants off rock faces in mountainous regions. They will sometimes allow commensals to grow on their backs to complete the illusion that they are just another part of the landscape. Even if detected, they are almost as tough as they look and are very difficult to pry off.

Seaglass thrax


Seaglass thraxes and their relatives are a common feature on the continent of Pandaros and Deiphobus. They spend their lives foraging for grubs, thraxes, and mobile fruits. A symbiosis with blue mold gives them their blue-green coloration and makes them mildly poisonous to most predators.

Blue Footed Thrax

Specimen 3.24

We found this pudgy thing in the leaf litter at Base Cliff. It made only a token effort to get away, suggesting that it might rely on other means to defend itself – namely poison. Its color would camouflage it well on some parts of Earth but here, there’s nothing subtle about it. Its feet are bright blue. It makes a surprising amount of noise when it walks over dry leaves. The gills on its back undulate in an eye-catching way while in motion, possibly helping to oxygenate the capillaries when the animal needs it the most. Little else is known, as we did not collect this specimen for study. Priority goes to dead or sick animals, and plants. Only in special cases will we need to kill. More on that later. (Alex O’Hearn, biologist, Odyssey I)

Specimen 3.24 (2)

Hognose Thrax

HognoseThe hognose thrax is a semi-arboreal plant eater not unlike squirrels: it can scamper up and down trees with its fourteen clawed feet and cache food to be located later with the help of an olfactory fringe lining the base of its double snout. Dextrous mouthparts enable it to capture and manipulate all sorts of food items.

Assorted Clawed Thraxes

Western Yellowbelly

Western Yellowbelly

Tree-Hair Louse

The tree-hair louse taps into the microphylls of black plants to access sugars and nutrients that pass through the plant’s bloodstream.

Cole's Trapeze Artist

Cole’s Trapeze Artist

Five-Star Sheararm

Five-Star Sheararm

old man thrax

Old Man Thrax

Blue Slimer

The blue slimer is a rare predator in a clade dominated by plant eaters and detritivores. A sticky mucus secreted from the heat pits traps small prey items, which the animal either devours immediately or stores for later consumption.

Assorted Microthraxes

Delta Siltsifter

Delta siltsifter

Delta Crawthrax

Delta crawthrax, a predator of the siltsifter



Pink and Blue Bristlefoot

Pink and blue bristlefoot, a detritivore with irritating hairs on its feet



Zipper Mouths

Zipper mouths. The entire length of their digestive tract opens to the outside. Even though it is derived from a one-way gut, it functions more as a blind gut for filtering sediment at the bottom of the ocean.

Assorted Tube-Footed Thraxes

Constrictor and Prey

A ghostly constrictor embracing its prey

Black Belt

Bayou black belt


White-faced brachyderm


Whipple, named for its mating call. The tympanum is brightly colored in near-infrared.


Common trailblazer, named for the scars it leaves on plants as it feeds.

Stack-Eyed Thraxes

Cavern gillback

Cavern gillyback

Hidden Lake cetus

Hidden Lake cetus, a large, sharklike bottom feeder

Mossy cetus

Mossy cetus, an ocean dweller that can reach lengths of five meters or more. The hair is a sophisticated gill system that doubles as camouflage in the weedy shallows of Aeneas’ west coast.


Mating display of the ringmaster

Reverse sawfish

Three species of reverse sawfish


The juggler feeds exclusively on the haploid fruits of the black pearl bush. The bush supplies the juggler population with an unpredictable supply of seeds, forcing the animals to cache seeds for later consumption. Seeds that aren’t eaten soon enough will mate and germinate into the next generation of black pearl bushes.

bulbous stackeye

Bulbous stackeye

Serpentine stackeye

Serpentine stackeye


Salmon stick-stack

Hidden Lake Cetus

hidden lake cetus

“Almost two centuries ago, an explorer fell into a hidden lake on the continent of Pandaros and encountered an entity she could not see, only feel as it passed. She described it as “long,” “sharklike,” and “silent.” The crew was not outfitted for a proper dive so the nature of the beast would have to remain a mystery – until now.

At only 55cm long, the S6 is the smallest submersible deployed by the Helen of Troy. After spending four days combing the bottom of Hidden Lake, the probe returned footage of an animal that matched the description provided by the explorer. It is undoubtedly a thoracostome and appears to be related to the mossy cetus, an oceanic species that can be found off the coast of Aeneas.

That Sinking Feeling
The bottom of Hidden Lake is dark – so dark that plants would struggle to gather enough sunlight to grow and sustain themselves. So why are there plants on the lakebed? Because it is not always this way. Periodically the surface mat loses its integrity to heavy grazing or severe weather, leaving islands of crimson buoyphyte (Stagnicorium puniceum) to float among loose vegetation, mostly germinating calaveras and Carellos’s buoyphyte (Zygophyta laxa). The light gives the plants the energy boost necessary for reproduction. At other times, the plants live as heterotrophs, trapping detritus and plankton in their gill-like leaves.

The ghostly figures swimming above the vegetation are Hidden Lake cetuses. These gentle serpents feed on the fruits of lakebed calaveras and anything else slow enough to capture. They use the cloak of darkness and silence to evade predators, as they cannot defend themselves in a fight. They are intelligent and naturally curious. If a stranger is not a known predator, they will gather in small groups to investigate, either in search of food or simply a novel experience. Decades after their first encounter with a human explorer, Hidden Lake cetuses were studied in depth by a Helen of Troy probe.

And that’s just in one tiny lake…

Mossy Cetus


While on a dive off the coast of Aeneas, oceanographer Navpreet Bhavishya attracted the attention of a large sea serpent.

“I saw a dark figure in the distance, like a shark but with more fins and what looked like a carpet of moss on its back,” she reported. “And it got closer. And bigger. I tried to freeze but the current swept me up and gave my position away. I knew it would be fruitless to try and outswim it so instead I grabbed a handful of hair and held on as best as I could.”

Her mission was to install an instrument that would track the seismic activity of a nearby convergent plate boundary. The installation was cut short when the animal, later identified as a thoracostome, carried Bhavishya twenty meters from the site.

“It was a wild ride, I tell you. I couldn’t figure out if my steed was trying to shake me off or if that’s just its normal speed, but it was fast. I let go when we hit the surface. The sea monster didn’t try to eat me like I feared; it just swam off. I think we were both relieved to be rid of each other.”

Bhavishya returned to the Starrus unharmed. The operation will resume tomorrow if the safety committee approves it. If not, the crew will move the instrument to a safer location.The seismometer’s monitoring camera caught a brief glimpse of Bhavishya before the thoracostome carried her out of sight

black and whiteThe seismometer’s monitoring camera caught a brief glimpse of Bhavishya before the thoracostome carried her out of sight.






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