Spiridon was a planet adopted by a base by the Daleks in the early 26th century as a part of their plan to destabilise the existing galactic balance of power prior to an invasion in force.
Astronomical and Geological Data
Spiridon's exact location was never revealed, but given the nature of the Dalek plan it seems likely it was in Mutter's Spiral, relatively close to the empires of Earth and Draconia.
Spiridon had an unsual geology in that its core was composed of molten ice. This would occasionally erupt onto the surface through fissures known as icecanoes.
Indigenous Life Forms
Non-intelligent Life
The planet was home to a number of non-intelligent predators, most of which were nocturnal. Many of the plant species also exhibited signs of sentience and were dangerous in their own right. One such species spat a mycogenic compound at anything which moved too close. The mould resulting from direct contact with this substance grew rapidly across the skin of anyone struck, rapidly incapacitating before eventually killing them.
Intelligent Life
The natives of the planet were known as Spiridons and were notable for being invisible. This was apparently an inherent characteristic, probably generated as part of essential life processes as it ceased to function post-mortem.
It nclear whether the Spiridons had an additional compensatory sense or were actually invisible to each other as well (in which case their social interactions and reproductive behaviour must have been especially challenging). The former seems somewhat more likely as at least one native plant species had evolved the ability to detect invisible life forms.
When initially encountered by the Didons had been enslaved by the Daleks and so the nature and level of their native culture prior to this is unknown. It did not appear to be more sophisticated than a primitive tribal society.