The Mechanical Bio-arm resembles an arm but being made of metal. It also has fingers and a red button on it to activate it.
Role in episode
Plankton attempted to use the bio-arm in a way to help get the secret formula from the Kelpshake restaurant. However, the bio-arm ends up malfunctioning causing an upset Plankton to press the red button repeatedly. However, this ends up causing the bio-arm to slap Plankton a bunch of times.