The Late Tristagmacene

The Cyanophytes

The Cyanorezas

By the late Tristagmacene, cyanophytes of all kinds flourished across the myriad oceanic environments. Cyanostirps like Gelidostirpis (Cold Branches) thrived in frigid waters, their thick, branching structures coated in protective mucus layers to withstand extreme polar temperatures. These hardy cyanophytes formed dense thickets in polar shallows, providing shelter for various benthic organisms. 

Long-armed species of cyanocaputs, like Gelatinacaputis (Soft Heads), developed broad, gelatinous appendages that swayed with the currents, maximizing surface area for photosynthesis while also serving as nutrient traps, catching organic particles drifting through the water. These delicate, translucent fronds gave them a ghostly appearance, particularly in the twilight depths where they were most common.

Some descendants of cyanodirects, such as Schoenhamusis (Reed Hooks), evolved thicker, bark-like stems that provided structural support in turbulent waters. At their tops, these sturdy stalks bore softer, hook-shaped structures, which served multiple functions-stabilizing the organism by latching onto rocks or other cyanophytes and enhancing nutrient absorption. These adaptations allowed Schoenhamusis to dominate many shallow coastal zones, forming dense, swaying fields of cyanophyte “reeds."

The Cyanocomas

The cyanocoma, the many-haired relatives of the cyanoreza, had also been undergoing evolution in the background over the past hundred million years. Pushed into more specialized niches by the dominance of cyanoreza, these cyanophytes diversified through a variety of unique adaptations.

One startling adaptation was the evolution of Celophytis (Veil Plants). These gargantuan floating autotrophs have evolved to float on and under the ocean's surface, stabilized by their long flowing hairs, slowly photosynthesizing as they go, creating vast drifting ecosystems that span the open oceans. Their long, flowing hairs act as stabilizers, slowing their movement and providing shelter for countless marine organisms. Small filter-feeders cling to their strands, grazing on planktonic life carried by the currents, while larger creatures lurk beneath their expansive canopies, seeking refuge from predators. The shaded waters beneath a celophyte often become nurseries for juvenile organisms, protected from the harsh sun and open-sea predators. 

Over time, different species of celophytes have evolved specialized adaptations to suit their environments. Some, like Celophytis Magna (Great Veil Plant), grow to massive proportions, their broad bodies spanning dozens of meters and forming stable floating islands. Others, such as Celophytis Minora (Small Veil Plant), have a more ephemeral existence, their delicate bodies drifting in seasonal blooms before fragmenting and spreading across the oceans. Some, like Celophytis Subvelata (Subsurface Veil Plant), drift just below the ocean’s surface, their semi-buoyant forms maximizing light absorption while avoiding surface disturbances. Some species have even developed symbiotic relationships with heterotrophic organisms, such as small lithoflora that attach themselves to their surface, or mobile creatures that help clean and protect them in exchange for shelter.

The Lithoflora

The lithoflora have continued to diversify into the Tristagmacene. Propafloris (Spreading Flowers) is a group of lithoflora which has become softer, more gelatinous, spreading across its benthic environment. Unlike their rigid relatives, propaflora rely on flexibility rather than structural strength, sprawling outward in interconnected mats that extend tendrils into their surroundings. This adaptation allows them to efficiently capture nutrients from the water while also fostering symbiotic relationships with small heterotrophs that burrow within their pliable surfaces. Some species have evolved slow, amoeba-like movements, inching across the ocean floor over generations to seek out nutrient-rich areas. Others have specialized in enmeshing detritus, forming the base of entire benthic ecosystems by providing both food and shelter for scavengers and filter feeders.

By contrast, Ardufloris (Towering Flowers) have taken an opposite approach, becoming increasingly dense, robust, and enormous. These lithoflora have developed thick, calcified trunks that anchor them deep within the seabed, allowing them to grow to towering heights. Their immense size grants them access to stronger ocean currents, where they can more effectively filter nutrients and house symbiotic autotrophs. Some arduflora have developed hard, shell-like exteriors, forming protective reefs that shelter entire communities of marine life. Others have evolved layered, porous structures capable of capturing drifting plankton, essentially functioning as passive suspension feeders. 

The Serpostomes

The serpostomes, some of Atmos's strangest creatures, have, despite their suboptimal body plans, found some success during the Tristagmacene. Teterstomis (Repugnant Mouths) have developed potent toxins along their tentacular surface structures. On contact, these toxins cause intense irritation or paralysis in potential predators, deterring attacks and granting the teterstomes a degree of protection despite their otherwise vulnerable anatomy. To warn would-be predators, they have evolved striking aposomatic coloration, with their tentacles taking on a vivid, unnatural green hue. This starkly contrasts with the dominant blue tones of the surrounding cyanophytes, making teterstomes stand out in the benthic environment as an unmistakable threat. Some species have even refined their defensive strategy further, developing bioluminescent warning flashes that activate when disturbed, reinforcing their toxic reputation.

 While the teterstomes remain firmly attached to the ocean floor, another lineage, Spheristomis (Sphere Mouths), has entirely abandoned the benthic environment in favor of the open ocean. These unusual creatures have evolved an internal buoyant sac, which allows them to float effortlessly in the midwater column, drifting along currents in pursuit of falling detritus and marine snow. Their tentacles, rather than aiding in locomotion, have become specialized for passive feeding, extending outward like a net to trap organic particles as they descend from the upper ocean layers. This adaptation has allowed spheristomes to exploit a previously inaccessible niche, where competition is lower and food is abundant. Some species have even begun forming slow-drifting congregations, resembling eerie, floating colonies that glide through the depths in search of sustenance.

The Platyglosses

Platyglossis (Plate Tongues) is a small, agile descendants of the luranitrior's lineage. They have evolved eight eyes, which are arranged in pairs along either side of its broad, flattened head, sitting atop short, flexible stalks, granting them an expanded field of vision. This adaptation allows them to detect both prey and predators from multiple angles, reducing blind spots and increasing their awareness in the chaotic ocean environment. They undulate like flatworms, rippling their flat bodies above the sea floor.

The defining characteristic of the platyglosses is their long, flattened tongue, a muscular, plate-like structure that extends from their anterior mouth. Forked down the middle, this plate tongue is both a sensory organ and a feeding tool. It is covered in fine, hair-like structures that allow it to detect chemical cues in the water, much like the tongues of Earth’s snakes. The platygloss's feeding strategy is simple but effective-using its bifurcated tongue, it sweeps along surfaces and into crevices, trapping small invertebrates and organic debris before drawing them into its mouth. 

As active, free-swimming foragers, platyglosses fill a niche comparable to that of small predatory fish on Earth. Some species specialize in hunting microscopic plankton, while others use their acute chemical detection to track down soft-bodied prey buried in the sediment. Though they remain relatively low on the food chain, their agility and heightened senses make them elusive prey.

Tristags of the Tristagmacene

By the end of the Tristagmacene, the miruverms and pleruplods had adapted into a variety of forms, coming to occupy the myriad niches available to what is traditionally considered to be animal life. This epoch saw the evolution of the most notable clades of the tristag's descendants, who would, over the next several hundred million years, go on to dominate Atmos.

The Miruverms

Segnivermis

Segnivermis (Sluggish Worms) is a lineage of miruverms that has dramatically reduced in size, adapting to a planktonic or nektonic existence depending on the species. Despite their diminutive stature, most segniverms have retained the distinctive five-segmented body structure of their ancestors, though their anatomy has become more delicate and translucent to aid in buoyancy. Their thin, flexible bodies undulate with the ocean currents, allowing for passive drifting in some species, while others have developed limited swimming abilities to navigate through their pelagic environments. 

To enhance their mobility, certain species of segniverms have evolved two or three pairs of small, fin-like arms extending from their central segments. These appendages function as rudimentary paddles, helping them maintain stability and direction as they move through the water column. Despite their sluggish nature, they are efficient micro-predators, feeding primarily on other planktonic organisms, including smaller proto-heterotrophs and drifting cyanophytes. Some species use their flexible appendages to ensnare prey, while others rely on cilia-like structures to generate microcurrents that funnel food toward their mouths. 

However, segniverms are not just  predators, but also a primary food source for larger plankton-feeders and small nektonic organisms. Their abundance makes them a crucial link in the Tristagmacene marine food web, supporting a wide range of filter-feeders and active hunters alike. Some species have adapted defensive mechanisms to reduce predation pressure, including transparent bodies for near-invisibility or bioluminescent flashes to startle would-be attackers. Others rely on sheer numbers, reproducing in vast swarms to ensure the survival of their lineage despite heavy predation.

Velovermis

Velovermis (Fast Worms) is another descendant of the miruverms. This clade has adapted to fill the role of fish-like organisms in Atmos’s oceans. Unlike their sluggish relatives, these streamlined swimmers have evolved into swift, agile predators and foragers, using undulating movements to propel themselves through the water. Their once-flexible tail segment has been refined into a powerful horizontal fin, allowing for sustained swimming and rapid bursts of speed when evading predators or pursuing prey. 

To further enhance their hydrodynamic efficiency, many veloverms have begun to develop a fusiform body shape, reducing drag as they slice through the water. Many species exhibit countershading, a camouflage strategy where the dorsal side is darker-often in shades of deep blue or gray-to blend with the abyss when viewed from above, while the ventral side is lighter-taking on pale silver or white hues-to match the bright surface waters when seen from below. This adaptation provides crucial protection from both aerial and aquatic predators in the open ocean. 

Most veloverms are active hunters or filter-feeders, depending on the species. However, many species are herbivorous, feeding on cyanophytes, poremorphs, detritus, and other available nutrients. Their ecological role varies depending on the species: smaller veloverms may dart through plankton blooms, feeding on drifting microorganisms, while larger species pursue small nektonic creatures, using bursts of speed to ambush their prey. Others have evolved schooling behaviors, moving in synchronized groups to confuse predators and increase survival rates. 

As veloverms continue to diversify, they represent one of the most successful nektonic groups on Atmos, marking a dramatic evolutionary leap from their slow-moving, bottom-dwelling ancestors into the planet’s open waters. Their efficient swimming will enable them to dominate Atmos's open seas, and will open up to them a host of unfilled niches.

Dumbocoronis ("Dumbocrowns")

Dumbocoronis (Dumbo Crowns) is a distinctive lineage of miruverms that has evolved a distinctive mode of locomotion, utilizing powerful jet propulsion. Named for the large, ear-like propulsors on either side of their head segments, these structures have been repurposed from their ancestral breathing pores. In a dramatic shift from their more primitive relatives, dumbocrowns have developed a sophisticated water intake and expulsion system, allowing them to propel themselves forward with short, forceful bursts. 

Their propulsion system functions by drawing water in through their mouths and then forcefully expelling it out the back through the modified lateral openings. This adaptation enables the dumbocrowns to achieve rapid acceleration, making them capable of quick getaways from predators and sudden lunges toward prey. Unlike species that rely on constant fin-powered swimming, these creatures move in a rhythmic, pulsed motion, gliding between bursts of propulsion. To improve control and stability, dumbocrowns have also developed fin-like extensions at the ends of their tails, which help them steer and maintain balance as they navigate their midwater environment. 

Their jet-powered locomotion has allowed dumbocrowns to spread into a variety of oceanic habitats, from coastal shallows to deep, pelagic waters. Some species have evolved elongated, ribbon-like bodies that maximize hydrodynamic efficiency, while others remain more compact, using rapid, successive pulses to hover and dart in place. Their crown-like head structures, formed by their enlarged propulsion pores, serve additional functions beyond movement. In some species, these structures are brightly pigmented, used for signaling during mating displays or as a warning to deter predators. 

Ecologically, dumbocrowns species vary in their feeding strategies. Some are opportunistic predators, lunging at small nektonic organisms with surprising bursts of speed, while others have adopted a more passive filter-feeding approach, drifting through plankton-dense waters and using specialized mouth structures to sieve food particles. Their large, sensitive eyes allow them to track movement in dimly lit environments, and in some deep-sea forms, they have developed an enhanced capacity for detecting bioluminescence, helping them locate prey in the darkness.

Mystacevermis

Mystacevermis (Mustache Worms) have, unlike many of their cousins, remained largely basal and firmly benthic, evolving specialized adaptations to thrive along the ocean floor. The mystaceverms most distinctive feature is a pair of fully motile tentacular appendages flanking their mouths-highly flexible, muscular structures bristling with sensory hairs. Though originally adapted for digging burrows, their "mustaches' have since been repurposed to function both as delicate feelers, detecting vibrations in the substrate, and as prehensile limbs, actively grasping, manipulating, and even restraining prey. Some species use their appendages to sweep through the sediment, stirring up hidden invertebrates before snatching them between their mustaches, while others rely on a more passive feeding strategy, extending their mustaches to filter organic particles from the water. 

Unlike their more streamlined, free-swimming cousins, mystaceverms move in a slow, deliberate manner, undulating their segmented bodies across the ocean floor. In soft sediment environments, they use their mustaches in a more traditional burrowing role, scooping sand aside as they push forward with their bodies. Some species have evolved a flattened body plan, allowing them to slide effortlessly through narrow crevices in rocky benthic zones, while others have retained a cylindrical shape, favoring a life of slow, methodical burrowing. 

The Pleruplods

Velicatiplodis

Velicatiplodis (Pincer Legs) is a lineage of pleruplods that have diverged from their many-legged ancestors to specialize as agile benthic predators. Their most striking adaptation is the transformation of their frontmost pair of legs into prehensile pincers, giving them the ability to grasp, manipulate, and subdue prey. This shift in morphology has allowed them to occupy a variety of predatory niches along the ocean floor, where they actively hunt or scavenge. 

Unlike their detritivorous and omnivorous relatives, velicatiplods are primarily carnivorous, using their pincer-like appendages to seize small benthic organisms, including soft-bodied prey, shelled invertebrates, and even smaller members of their own lineage. Some species have developed strongly serrated pincers, allowing them to crush tougher exoskeletons, while others have evolved elongated, needle-like graspers suited for piercing and pinning down slippery prey.  

Their remaining pairs of legs, still numerous, retain their original hydraulically-assisted locomotion, providing stability and agility as they navigate the seabed. Some species have become ambush predators, lying partially buried in sediment and striking at unsuspecting prey with lightning-fast pincers. Others are more active hunters, scuttling across the ocean floor in search of food. 

Lutumplodis

Lutumplodis (Scavenger Legs) is a lineage of pleruplods that has adapted to a detritivorous lifestyle, specializing in scavenging and consuming organic debris along the ocean floor. Unlike their more predatory relatives, such as the velicatiplods, these creatures have evolved to be lower to the ground, hugging the benthic surface as they navigate through dense underwater vegetation, rocky crevices, and buried detritus in search of food. 

Their thirteen pairs of legs, originally adapted for walking and stability, have become more flexible and finely articulated, allowing them to scurry nimbly across the seabed while also being able to dig and sift through sediment. Some species of lutumplods have developed shorter, stouter legs for slow but deliberate movement, well-suited for burrowing into soft seabeds in search of decaying plant matter and animal remains. Others, dwelling in harder substrates, have longer, more slender legs, helping them navigate coral-like lithoflora formations and tight crevices where detritus accumulates. Their external spinal shell, once a prominent feature of their ancestors, has been significantly reduced, evolving into a smaller, more flexible dorsal plate. This change enhances their ability to squeeze into tight spaces, making them particularly adept at exploiting food sources in areas larger-bodied scavengers cannot reach.