Lethe Cavern is a highly exotic and dangerous environment.

Some stalactites are heavy enough to cause damage and unstable enough to fall if disturbed.

Watch out for weakened cave surfaces that can collapse when stood upon or impacted by significant force.

Highly acidic fluids sometimes collect in dangerously corrosive pools.

These slimy limeforms periodically drip dangerous acid. The Cladiotreme are extremophilic microbes that propagate through hairline fractures in rock. They collect in colonies that digest minerals and produce as a byproduct concentrated sulfuric acid, which has considerable corrosive properties.

Sufficient water can cause Acidic Slime to stop dripping temporarily by unbalancing its metabolic process.

Extremely high temperature molten rock, presumably sourced from deep underground, either the mantle or core-mantle boundary.

Pockets of gas trapped under magma will sometimes cause a periodic explosive eruption, ejecting a projectile of molten rock. Watch for the telltale sparks that precede an eruption.

Sufficient water can solidify a thin crust over a magma emitter, temporarily blocking the production of fireballs.

These hardy lifeforms grow across narrow sections of the cave, completely sealing them with a thick, filmy membrane. They are classified according to the Biomass level at which they open. Cerebrane are selectively porous and osmose nutrients out of the air. The biological compounds they consume are produced in higher concentrations as Biomass is created locally, and once a threshold is crossed, they retract into a later stage of their life cycle.

The thinnest species of Cerebrane, it retracts when Biomass concentrations exceed threshold 2.

The most common species of Cerebrane, it retracts when Biomass concentrations exceed threshold 3.

A thicker species of Cerebrane, it retracts when Biomass concentrations exceed threshold 4.

The thickest species in its genus, this Cerebrane retracts when Biomass concentrations exceed threshold 5.

This Cerebrane genus thrives in very specialized locations where the cave interior meets the more hostile surface environment. They are selectively porous, allowing large biotic material to pass with some effort but effectively preventing heat and gasses from escaping the cave.

Locations where Zoa can be planted. A given Zoa species will take root in some but not other types of Fertile Terrain. Fertile Terrain is classified according to its nutritive properties and pH level. A class of small and microscopic organisms called Echnia perform a similar function to those on Earth which break down bedrock into usable soil. Where Echnia thrive, Zoa can anchor and extract sustenance.

Fertile Terrain that has not been exposed to water. This is an alkaline Fertile Terrain.

Dry Fertile Terrain that has been exposed to water, increasing its nutritional value. Zoa planted in Wet Fertile Terrain tend to produce more biological activity than those planted in Dry Fertile Terrain. This is an alkaline Fertile Terrain.

Fertile Terrain that is highly acidic. Only certain classes of Zoa can grow in this type of terrain.

Fertile Terrain that is extremely high in nutrients. Zoa planted in Enriched Fertile Terrain always produce more biological activity than those planted in Wet or Dry Fertile Terrain. This is an alkaline Fertile Terrain.

Compost is the nutrition-rich byproduct of deceased lifeforms, those consumed by Larian. Throw Compost at any alkaline Fertile Terrain to convert it into Enriched Terrain. A complete lifeform, such as a Phyte, is masticated by the Larian and the remnants are ejected covered in digestive enzymes. These enzymes attract organisms which quickly break the organic matter down into Compost.

Fertile Terrain that is currently unusable such that no Zoa will grow in it. When conditions are unusually dry or cold, Echnia enter a regressive, dormant state in which they do not convert rock into nutrients. Major increases in heat and water will revive them.

Biomass 15 or (when watered) 20. These Zoa consume available minerals in the rock and release gasses (primarily nitrogen and oxygen) as waste. Like most Martian lifeforms, the Zoa class are neither true plants nor animals and are characterized by extremely rapid growth between life stages and superior metabolic efficiency.

These can be planted in any alkaline Fertile Terrain, where they will grow into new Halid Zoa. Similar to an Earth seed or egg, they contain the Halid embryo and stored nutrients encased in a protective coat. Under tranquil conditions, Halid Seeds transfer almost nothing with their environment, existing in a stasis.

Halid grown in Wet Fertile Terrain, such as those watered by thrown Hydron Seed, will produce new Halid Seeds. The process of absorbing water improves the Halid's size and biological activity, increasing their biomass contribution from 15 to 20. A Halid will continue producing seeds until it has created 2 viable offspring.

Halid Zoa can be damaged or destroyed by significant impacts and explosions or conditions of extreme temperatures or acidity.

Vapors released by Halid Zoa can reverse damage to human tissue and the GSA exploration suit. The vapors are automatically collected, processed, and applied by experimental hardware installed in the suit for this purpose.

Halid Zoa are especially responsive to the nutrients in Enriched Terrain. Enriched Halid exhibit the following properties: increased size and biological activity, +20 Biomass, extra seed production.

Biomass 10. Hydron Zoa have the remarkable ability to extract chemical nutrients from Fertile Terrain and metabolize it into liquid water, which they store abundantly in mucilaginous substances and partially release into their surroundings as vapor.

The seeds produced by Hydron Zoa will burst upon high impact with a hard surface, soaking the nearby area in water. Thus they form a convenient way to transport water and target its application. The seeds contain the Hydron embryo, nutrients stored in a mucilaginous substance, and a thin protective film on the outside. Undisturbed Hydron Seeds transfer almost nothing with their environment, existing in a stasis.

Hydron Seeds can be planted in any alkaline Fertile Terrain and quickly grow to a mature Hydron Zoa which will begin producing new seeds immediately. A Hydron will continue producing seeds until it has created 3 viable offspring.

Hydron Zoa can be damaged or destroyed by significant impacts and explosions or conditions of extreme temperatures or acidity.

Hydron Zoa grown in Enriched Terrain exhibit the following properties: increased size and biological activity, +5 Biomass, extra seed production and increased seed ejection velocity.

Biomass 5 per Phyte. Phyta are a class of mobile lifeforms that are shy and tend to appear in groups. They are radially symmetric, consisting of a central disc surrounded by several legs whose clinging strength enable a Phyte to walk on vertical surfaces and jump great distances. Phyta sense their surroundings using a process similar to echolocation which is both produced and received by the same pair of antenna emerging from their apical end.

Dormant Phyta awaken at Biomass 2. Phyta are often encountered in a dormant state of remarkably low biological activity which seems to have enabled them to survive hostile conditions, in some cases for billions of years. When the local environment reaches Biomass 2, Phyta detect the increased habitability and awaken into their active state. A dormant Phyte is collapsed into a tightly-folded shape in order to minimize exposure.

Phyta subsist by consuming the seeds from several of the Zoa class of lifeforms. A Phyte's central disc consists of a structured lattice of semi-rigid connective tissues which can expand and collapse like an umbrella. At full expansion, the basal side of the disc opens into a large gastrovascular cavity. A seed inside this cavity is digested through a combination of mastication and enzymatic secretion.

Phyta reproduce asexually. After they eat, Phyta produce an egg which quickly hatches into a mature new Phyte.

Phyta reproduce quickly and have no special protection, therefore they are the target of predation by other Martian lifeforms. Their tendency to withdraw from human presence can be leveraged to herd them into contact with their predators.

Phyta prefer to be dry. A Phyte that becomes wet will engage in a drying ritual to shake water off of its body.

A Phyte that consumes a Feran Seed will explode. This poorly adaptive behavior is not fully understood. It is being investigated whether Feran and Phyta could have evolved during disconnected epochs of Martian history.

Biomass 40. The acidophilic Prax Zoa are one of the top predators of Lethe Cavern, consuming smaller lifeforms. They have been described as "aggressive" and "curious." They have prehensile stems that move quickly to attack prey and repel threats. Because Prax Zoa only take root in Acidic Fertile Terrain, they have no Enriched Form.

Prax Seeds can be planted only in Acidic Fertile Terrain, where they will grow into a new Prax Zoa. Similar to an Earth seed or egg, they contain the Prax embryo and stored nutrients encased in a protective, rubbery coat. Under tranquil conditions, Prax Seeds transfer almost nothing with their environment, existing in a stasis.

A Prax Zoa will produce one Prax Seed for every mobile lifeform it consumes.

Prax Zoa consume Phyta and Cycots. After eating, Prax enter a temporary regressive state of low activity, during which they exhibit no hostile behaviors. Prax also consume Feran Seeds, which causes the Prax to explode. This poorly adaptive behavior is not fully understood. It is being investigated whether Feran and Prax could have evolved during disconnected epochs of Martian history.

Prax Zoa attack other lifeforms that come within their range, including humans, by stabbing with their sharp helical tusk. They appear to have adapted this behavior both to consume prey and as a defensive mechanism.

Prax Zoa can be damaged or destroyed by significant impacts or conditions of extreme temperature or alkalinity. They are not damaged by acid or explosions.

Prax Zoa engage in the remarkable practice of picking up loose objects within their range and throwing them. This response can be leveraged to distract a Prax Zoa from making an attack. This behavior has been hypothesized to be an adaption which keeps their territory clear of potential competitors within their ecological niche.

Biomass 30. Larians are an immobile class of lifeform found exclusively on cave ceilings. They are one of the top predators of Lethe Cavern and snare prey by lowering a sticky, glowing tendril. The majority of their body is encased in a nest burrowed out of solid rock, with only their armored mouths emerging. Larian reproduction is extremely slow, involving a centuries-long larval stage.

Dormant Larians awaken at Biomass 2. Larians are often encountered in a dormant state of remarkably low biological activity which seems to have enabled them to survive hostile conditions, in some cases for billions of years. When the local environment reaches Biomass 2, a Larian responds by waking into its active state. A dormant Larian is extremely durable and cannot be harmed.

Larians prefer to eat mobile lifeforms but are also able to derive some nutritional value from Zoa seeds. Larians lower a glowing tendril to attract prey. Victims become stuck in the sticky tendril and drawn up into the mouth of the Larian to be consumed. Larians have not yet been observed attempting to digest humans, but becoming trapped in a Larian tendril can be damaging or even fatal.

A Larian can be damaged or destroyed only by explosions and only then when its mouth opens to consume prey. Destroying a Larian is the only known method for forcing it to release you if you become stuck in its tendril. Larians are also destroyed when they consume Feran Seeds, which are poisonous to them.

A Larian who consumes a Hydron Seed will become overly saturated and releases excess water into its local environment, which can have side effects on other nearby lifeforms. Larian digestion requires a careful balance of moisture, so Larians are constantly engaging in processes to regulate their internal water volume.

Biomass 35. Ledon Zoa are distinguished by their seeds, which are inflated, buoyant and fragile. The seeds rise upward with respect to gravity, which results in a symmetric propagation pattern relative to that of other Zoa. Ledon are the largest species of alkaline Zoa and produce abundant biological compounds, especially when they take root in nutritious environments.

Ledon Seeds that land in any alkaline Fertile Terrain will grow into new Ledon Zoa. The seeds float upward and cannot be picked up or carried. Ledon seeds are large and covered in a hydroscopic secretion which makes them too slippery to be carried, although they can be bounced through collisions. Ledon Seeds are prone to breakage, and they self destruct if they come to rest in a location that does not afford planting.

Ledon require additional nutrients to produce new Ledon Seeds, such as those provided by Wet and Enriched Fertile Terrain. Because the surplus nutrients are expended to produce the gaseous compound which inflates the Ledon Seeds, Ledon Zoa do not increase in Biomass when grown in Wet Fertile Terrain. A Ledon will continue producing seeds until it has created 2 viable offspring.

Ledon Zoa can be damaged or destroyed by significant impacts and explosions or conditions of extreme temperatures or acidity.

Enriched Ledon Zoa exhibit the following properties: increased size and biological activity, +15 Biomass, extra seed production.

Biomass 30. Feran Zoa thrive in extremely hot locations and possess the distinctive feature of producing explosive seeds. Because Feran Zoa only take root in Acidic Fertile Terrain, they have no Enriched Form.

Feran Seeds burst upon high impact with a hard surface, causing a dangerous explosion which can destroy fragile structures and damage lifeforms. The seeds can also be planted in Acidic Fertile Terrain to grow new Feran Zoa. The nutrients required for Feran growth are extremely volatile, which is what causes Feran Seeds to explode. Feran Zoa eject their seeds at high velocity as a defensive adaptation.

Feran Seeds can be planted in Acidic Fertile Terrain and quickly grow to a mature Feran Zoa which will begin producing new seeds immediately. A Feran will continue producing seeds until it has created 3 viable offspring.

Feran Zoa are hardy lifeforms that are typically destroyed only by conditions of extreme alkalinity, such as when the Fertile Terrain in which they have taken root transactivates from acidic to alkaline. They can also be damaged or destroyed by significant impacts or direct contact with acidic fluids. They are not damaged by explosions or sources of extreme heat.

A Feran Seed that makes contact with magma will erupt vertically in an explosive projectile.

Biomass 5. Cephad Zoa consist of two highly related subspecies, Acidic Cephad and Alkaline Cephad, named for the pH of Fertile Terrain they inhabit and spores they produce. Cephad spores have a tendency over time to destroy and replace existing Zoa, which can result in infestations. Despite this risk, Cephad are useful in that their spores are the only deliberate way to change the pH of Fertile Terrain.

Cephad seeds are lightweight, drifting spores that are either alkaline or acidic, matching the pH of the parent Cephad. A Cephad spore's interaction with a given piece of Fertile Terrain will vary depending on the pH of the spore and the pH of the Fertile Terrain. Cephad spores exhibit limited self-locomotion abilities, which they seem to employ primarily to repel away from unfamiliar stimulus.

A Cephad spore that comes to rest in Fertile Terrain with a matching pH will quickly grow into a mature Cephad Zoa. Therefore Acidic Cephad will grow only in Acidic Fertile Terrain, and Alkaline Cephad will grow only in the 3 types of alkaline Fertile Terrain. A Cephad will continue producing spores until it has created 2 viable offspring.

A Cephad spore that comes to rest in Fertile Terrain with the opposite pH will reverse that Fertile Terrain's pH level. Alkaline spores convert Acidic Fertile Terrain into Dry Fertile Terrain, and Acidic spores convert any alkaline Fertile Terrain into Acidic Fertile Terrain. These changes to pH level are likely to kill any Zoa currently planted in the affected Fertile Terrain, which allows for different Zoa to be planted.

Acidic Cephad spores are converted to Alkaline spores when they are exposed to sufficient water, such as from a burst Hydron seed. Cephad spore interiors are composed of spongin fibrils whose complex arrangement retains hydronium ions in solution. When saturated with water, the fibrils shed the ions and become extremely alkaline.

Alkaline Cephad spores are converted to Acidic spores when they are exposed to sufficient acid. Cephad spore interiors are composed spongin fibrils whose complex arrangement can retain hydronium ions in solution when saturated in a low pH fluid.

Cephad Zoa are hardy, adaptive lifeforms that are typically destroyed only by explosions, such as those from a burst Feran Seed. They can also be damaged or destroyed by significant impacts and conditions of extreme temperature. Cephad Zoa temporarily halt the production of spores when they become saturated in water, such as from a burst Hydron seed.

Cephad Zoa exhibit a minor response to Enriched Terrain, increasing +1 in Biomass and producing 1 extra spore.

Biomass 30 per Mobile Autobiote. The Cycot is the first confirmed example of autoapobiotic life, meaning that the complete lifeform consists of multiple Autobiotes: separate and autonomous biological units. The Cycot is composed of a single large Sessile Autobiote and several Mobile Autobiotes. The Mobile Autobiotes gather sustenance and provide protection, while the Sessile Autobiote produces new Mobile Autobiotes through a budding process.

This is the large, immobile portion of the overall Cycot lifeform. It can be compared to the central body of a more conventional lifeform, while the Mobile Autobiotes can be compared to the eyes and arms. Although it makes no direct biomass contribution, the Sessile Autobiote is able to produce new Mobile Autobiotes.

This is the smaller, mobile portion of the overall Cycot lifeform. When active, Mobile Autobiotes locomote by flying and patrol in search of sustenance. They are often found in a dormant state protected inside the Sessile Autobiote until their local environment reaches Biomass 2, at which point they detect the increased habitability and awaken into their active state.

Mobile Autobiotes patrol their local area in search of Zoa seeds, which they deliver to the Sessile Autobiote.

A Sessile Autobiote that consumes 4 seeds will create a new Mobile Autobiote. It is not known how an entire Cycot reproduces, but a given Cycot can produce new Mobile Autobiotes. The Cycot collects any 4 Zoa seeds, which are typically gathered by Mobile Autobiotes. The Sessile Autobiote consumes the seeds and forms a bud, which quickly matures into a new Mobile Autobiote.

The Mobile Autobiotes of a Cycot are a food source for other lifeforms found in Lethe Cavern. The tendency of Mobile Autobiotes to withdraw from human presence can be leveraged to herd them into contact with their predators.

A Cycot will attack to defend the Sessile Autobiote and its cache of seeds. A Mobile Autobiote that discovers any intruding lifeforms in the Sessile Autobiote will charge and spear the intruder with its sharpened tentacles.

A Mobile Autobiote of a Cycot can be damaged or destroyed by significant impacts and explosions, extreme temperatures, and direct exposure to acid. Sessile Autobiotes have no known vulnerabilities and appear to have an extremely long life span. It is not known whether a Cycot whose Mobile Autobiotes have all been destroyed has any innate means of producing new Mobile Autobiotes.

The MegaZoa are an order of Zoa that grow to extreme sizes compared to their smaller relatives. Each MegaZoa plays an active role in the Lethe Cavern environment, often in symbiosis with other MegaZoa species. For example, the Calamitocae activate the Feranmaxes, which then melt ice into water which is pumped by the Hydronmaxes. The Alveopyridae gather energy, which can activate Levitrophs. It is not yet understood how the MegaZoa evolved these interactions.

Scientific name: Calamitocae. These MegaZoa are covered in microscopic cilia which transfer gas and vapor samples between the exterior and interior of the Zoa. Their long root-like organs have prehensile properties. The Periscopes appear to have evolved in open air, such as a planetary surface, but due to extremely efficient metabolism and unprecedented physical durability, they have survived burial in basalt for billions of years.

These MegaZoa transport liquid water up through their long root-like organs using capillary action. Analysis suggests that the Hydronmaxes are the earliest evolved MegaZoa, with genetic evidence indicating that the Calamitoceae and the Alveopyridae descended from them. Further, the smaller and more efficient Hydron Zoa clearly evolved from the Hydronmaxis.

These incredibly heat-resistant MegaZoa transport magma up from an unknown source through their long root-like organs. Feranmaxes subsist on thermal energy from magma, and modify intake and output to regulate their temperature. All liquid magma presently found in Lethe Cavern has been transported by Feranmaxes.

Scientific name: Alveopyridae. These MegaZoa harvest compounds released by lifeforms in Lethe Cavern and convert them into electrochemical energy, which they partially consume for sustenance and send the significant surplus energy down their root-like organs.

These large and complex MegaZoa are found extensively in Lethe Cavern and are activated by the electrochemical energy provided by the Alveopyridae. They expand when activated, pushing upwards on the cave ceiling with tremendous force. The Levitroph are genetically distinct lifeforms, suggesting an atypical evolutionary history.