Traveller: Aliens: Deep Ones & Tcho-Tcho

Dagon, Deep Ones & Tcho-Tcho


Have a bunch of re-useable modified humans with a plausible back story to make it easier to flesh out worlds on the fly.


The UWP references the planet (or moon) in the system which is closest to Earth-like.

But what does earth-like mean?

If you look at the supposed history of earth

then (very roughly) you get 4.5 billion years split into
– 500 million years of hell world
– 3.5 billion of gradually increasing oxygen
– 500 million years of oxygen explosion

so roughly 80% of the time “earth-like” meant
– barren continents and islands
– carbon dioxide atmosphere
– mildly acidic oceans
– no ozone layer so lots of radiation

with a gradual transition to a more oxygenated world.

So if for the sake of argument potentially habitable planets / moons are often like that but a large majority are in their CO2 phase then that creates a neat and at least game-plausible reason for the Ancients to seed those systems with fire and forget biological terraformers.



So divide the oxygenation process into three stages for convenience and have the Ancients drop some humans modified to survive the conditions with some food source that speeds up the oxygenating process.

Early Stage 1)little oxygen, Dagon
No sea life yet. Large modified aquatic species living in deep water protected from the radiation and growing some kind of native microbial goop around hot vents in volcanic areas. Slow metabolism. Tolerates oxygen but doesn’t use it. No light, blind but mildly psionic.

Middle Stage 2) oxygenated oceans, Deep Ones
More oxygen, more ozone protection from radiation, lots of sea life, microbial goop farming in coastal waters. Come on land to breed in coastal caves or reefs, babies look relatively human, gradually take on Deep One characteristics as they mature.

Late Stage 3) early land colonization, Tcho-Tcho
Oxygenated oceans, beginning of microbial colonization of coastal land. Tcho-Tcho adapted for very thin atmosphere with lots of CO2 and limited oxygen. Short, barrel-chested, hyper efficient breathing – either dark-skinned, burrowing or nocturnal for the radiation (maybe all three). Grow native microbial goop.

Planets that were part way between 1 and 2 when they were seeded could have been seeded with both Dagon and Deep Ones with the Deep Ones ending up treating the Dagon as gods due to their psionic ability.

Low population density in all cases.


The names come from Cthulhu but the names of various of the canon minor races that fit could be used instead.



The terra forming process could gradually kill off the terra formers:

  1. The growth of sea life could lead to burrowing sea creatures who kill off the microbial mats except in certain locations.
  2. Some Deep Ones could adapt to hunting sea food.
  3. Some might die out leaving primitive underwater temples, carved corral reefs etc behind.
  4. Deepwater Dagons left behind.
  5. Various breeds of Tcho-Tcho adapted to local conditions separate from the atmosphere e.g. taller and spindly, short and stocky, furry.
  6. Tcho-Tcho may gradually retreat to high altitudes as oxygen increases



  • Deep Ones: stronger, tougher, rubbery skin, claws, bite, low to medium intelligence – C7C500, capable of using nets, coral daggers etc. If successfully breed with full humans – difficult but possible – they can be made smarter.
  • Tcho-Tcho: generally short, thin, barrel chest, membrane nose, ark skinned with other variations depending on other conditions – 575600

I’m going to treat some of the canon minor species as connected

I’ll say Luriani are standard Deep Ones and Aquaan and Nexies were created by Solomani / SuSaG breeding humans with remnant Deep Ones.



very thin and very thin tainted atmospheres

maybe thin and thin tainted

rare above that except remnant populations


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