The Star Scorpions, called the Androctonus Astra in High Gothic, was a Loyalist Space Marine Chapter of unknown genetic origin raised during the 25th Founding, the so-called "Bastion Founding". Upon their inception, they were one of three Chapters that made up the Adeptus Vaelarii, better known as the "Sentinels of the Veil," charged with standing sentinel over the scattered worlds of the region called Elara's Veil.
Unfortunately, due to extreme flaws in the coding of their gene-seed, the Star Scorpions proved unable to replace their numbers, at the same time that their entire Chapter fleet became trapped in the Warp and was destroyed by its inhabitants.
They are now considered extinct, a lost Chapter of the Adeptus Astartes. It is unknown what Chapter provided the gene-seed for the Star Scorpions' Founding and little other information about the Chapter is available in Imperial records. The Chapter's homeworld was called Khamun-Sen.
While trapped in the Warp, the Star Scorpions eventually succumbed to the temptations of the Chaos Gods and its survivors became a warband of Chaos Space Marines known as The Pure. They finally returned to realspace in the wake of the birth of the Great Rift in the Era Indomitus in command of a vast Chaos warhost of Human and mutant Chaos Cultists known as the Exilarchy.
With the aid of the Exilarchy, The Pure unleashed a war for control of Elara's Veil, hoping to reclaim for the Dark Gods the region they had once defended. Over a Terran century later according to the passage of sidereal time in the wake of the chronological aberrations created by the Great Rift, more than half of the region had fallen to their control. The remaining Chapters of the Adeptus Vaelarii -- the Emperor's Spears and the Celestial Lions -- found themselves struggling to maintain the freedom of the rest of the Veil.
Chapter History

Star Scorpions Chapter Colour Scheme as displayed by a Firstborn Space Marine.
Sentinels of the Veil
Following the inception of the Star Scorpions Chapter during the 25th Founding, they were became part of a triumvirate of Adeptus Astartes Chapters, including the Celestial Lions and the Emperor's Spears, known as the Adeptus Vaelarii or "Sentinels of the Veil."
The Sentinels were charged with standing watch over the worlds of Eldara's Veil, a backwater sector of the galaxy in the Ultima Segmentum. But eventually, the Star Scorpions would no longer be able to fulfill their oath-sworn duty due to their own genetic flaws that saw them fatally undone.
Death of the Star Scorpions
The Star Scorpions had the dual misfortune of producing highly mutated gene-seed that often made successful implantation of new Astartes impossible and being utterly devastated by Daemonic entities when the Chapter's fleet became trapped in the Warp.
The exact fate of the Star Scorpions is unknown. However, the High Lords of Terra decreed on behalf of the Emperor of Mankind that the Chapter should be considered irrevocably lost when the Adeptus Mechanicus proved incapable of using their corrupted gene-seed reserves to reconstitute them.
Reallocation of Chapter Number
The highly mutated gene-seed of the Star Scorpions hampered Imperial efforts to rebuild the Chapter and eventually the bio-engineers and chem-architects of the Adeptus Mechanicus were forced to concede defeat.
For a time it seemed that the Chapter number 888 would never be used again, but some Terran years later, with the 26th Founding of 738.M41 in the offing, the Mechanicus were persuaded to revisit the Chapter colours, number, and regalia, resulting in the creation of the Mentors Chapter.
The Mentors received the colours and number of the extinct Chapter but instead of the Star Scorpions' corrupted gene-seed, they were provided with an entirely new generation of genetic material collected from the storage banks of the Mechanicus' Terran laboratories.
Chapter Appearance
Chapter Colours
The Star Scorpions primarily wore forest green power armour which included the backpack, helm, shoulder pauldron trim, chest guard and groin. The shoulder pauldron insets, arms and leg armour were white. The Aquila or Imperialis on the chest guard was golden. The squad specialty symbol on the right shoulder pauldron was red.
The Star Scorpions used the same colour scheme as the current Mentors Chapter.
Chapter Badge
The exact appearance of the Star Scorpions' Chapter badge is not listed in current Imperial records, but is known to be some variant of a scorpion.
Sources
- White Dwarf 98 (UK), "Index Astartes - The Mentor Legion" by Bryan Ansell, Alan Merrett and Paul Cockburn
- Bolter & Chainsword Forums - Aaron Dembski-Bowden on the Emperor's Spears (Information on the Star Scorpions' Chapter badge)
- Spear of the Emperor (Novel) by Aaron Dembski-Bowden, Chs. V, VIII, XIV, XVII