The Doom II manual presents the Spider Mastermind as the mother of the Arachnotrons: ' You guess the Arachnotrons had to come from somewhere. Watch for it at the end of the third episode of DOOM, and numerous times times in DOOM II.'
The Official Doom FAQ (included in Doom 1.4) describes the creature as a 'huge robotic chaingun shooting spider,' adding 'it will make you wish you never were playing DOOM in the first place. Perhaps as a result of this, the manual for the Depths of Doom Trilogy erroneously states that it appears in Doom II only.
The Spiderdemon is not mentioned in the Doom manual, presumably to avoid a spoiler.
