A Mechadendrite is a catchall name that covers a variety of tendril-like prosthetics used by Enginseers and other members of the Adeptus Mechanicus. It assists in manipulation of objects, micro-construction, maintenance, research and defence. It is connected to the central nervous system of the Techpriest, and so is controlled through thought just like a biological limb.
Mechadendrites are constructed from metallic alloys and have small motors and actuators within their armoured structures. They are usually longer than the Techpriest's natural limbs and are with multiple joints (simulating mechanical tentacles) to allow maximum reach and flexibility. Members of the Adeptus Mechanicus from the Enginseer rank and above are known to have mechadendrites, and although they may often only have one fitted, one could have as many mechadendrites as the body will support.
Servitors can also have mechadendrites to assist the enginseer they are assigned to.