Retrorat

"Rodents Of Unusual Size? I don't think they exist."

A retrorat is a form of Cybertronic wildlife. A possible synonym or relation is the robo-rat.

Fiction

Generation 1 cartoon continuity

The Transformers cartoon

It's not nice to compare others Microbots or their parents to these creatures. Changing Gears

The Headmasters cartoon

Shortly after his resurrection, Optimus Prime went on a search with ghost-Alpha Trion for the chamber of Vector Sigma deep within the bowels of Cybertron. In one corridor, Alpha Trion was telepathically warned by Fortress Maximus not to continue that way, but since Optimus hadn't heard anything, they did not turn around immediately. Next Optimus knew, he was under attack by a mutant retrorat. The creature wasn't a problem to defeat on its own, but others of its kind swiftly followed. Smashing the creatures off him, Optimus suggested trying a different tunnel and promptly made a run for it. Birth of the Fantastic Double Prime

Beast Wars: Uprising

Labrat gained a retrorat alt-mode upon adopting the Beast Upgrade. Not All Megatrons Bisk came across mutant retrorats while exploring the bowels of Cybertron. The Inexorable March

Notes

Rats.

• A Cybertronic rat creature appears in the Marvel UK story "The Hunting Party". It is not given any designation, but since it's a rat on Cybertron, it just might be a retrorat.
• The retrorats in The Headmasters were not named as such in the episode, only being referred to as "harinezumi" (ハリネズミ, "hedgehog", literally "needle rat") on their model sheet. Their identification as "retrorats" came decades later in Beast Wars: Uprising.