Arachnatron: not natural fauna
Pictures coutesy of the UAC Survelliance Group
The Arachnatron was not a naturally-occuring species on the other side of The Portal; however, a number of specimins were found wandering within the Portal environment.
The Arachnatron is the creation of an alien intelligence, surgically combining the disembodied head and torso section of an unknown, possibly aquatic life-form with a platform containing 4 highly sophisticated, multi-segmented mechanical legs and a forward-facing plasma weapon.
The legs and weapon are not directly controlled by the brain. The actual control of the legs and weapon is performed by a centrally-located alien computer-like unit which functions as a ganglion. The biological half of the unit can, through signals sent to the ganglion, cause five total activities to be performed by the legs and weapon: ambulate forward, stand in one location, stand braced and fire the weapon, pivot to the left, and pivot to the right. The computer-like ganglion functions as a controller for the mechanical legs and weapon. This ganglion controls the foot placement, leg movement, and maintains the unit's balance, utilizing a multitude of positional sensors within the mechanical legs and feet. Each foot has several appendages which function both as the support structure for that leg as well as containing sensory devices that relay information about the terrain angle. The Arachnatron's leg and platform combination is capable of relatively complex feats of ambulation for a robotic unit, such as climbing stairs of varying step length relatively quickly.
Several groups of Arachnatron were found in the environment. Their purpose in the environment, if any, is unknown. They were seen walking around in groups of around 10 individuals, with their plasma weapons fully charged. What they eat and if or how they maintain the plasma weapons in a charged state is unknown.