Space slug

Space slugs are creatures deep within the bowels of Cybertron, serving as part of the planet's natural defense mechanism. Though incapable of communicating with Transformers, they are intelligent enough to recognize friend from foe, and are capable of utilizing friendly Transformers in their efforts.

Transformers: War for Cybertron
When Optimus Prime took Ironhide and Warpath with him to remove the Dark Energon threatening to contaminate Cybertron's core, they saw a space slug moving through the tunnels. Though Warpath was quite startled by their appearance, the newly appointed Prime reassured him that they only intended to destroy the Dark Energon crystals threatening the core.

Another close encounter came when a space slug burrowed through some crystals blocking the three Autobots and took out an attacking Decepticon. Ironhide tried the universal greeting, but the slug simply ignored them and continued with its task. Finally, the three Autobots encountered three slugs with turrets on their backs, wanting the Autobots to take control of the turrets. The slugs took the Autobots through Cybertron's tunnels, plowing through the Decepticon army Megatron had left to control the core. The three slugs were lost when a corrupted slug destroyed the floor they were on, sending the slugs and Autobots to the ground below.

Later, when the Autobots traveled further into Cybertron's interior, they witnessed a Decepticon attack a space slug.

At the core, the trio discovered that the same corrupted, mutated space slug encountered earlier had begun feeding on Cybertron's life force, granting it strange abilities. They managed to kill it, sending its corpse into the lake of Dark Energon. Although the threat had been defeated, the core informed Optimus that he was too late. The core would have to shut down to repair itself from the Dark Energon infection. Transformers: War for Cybertron (360/PS3/PC)