Here's a list of all planets that existed at some point in the universe's history that no longer exist.
Planet Beetledeo was a planet that was inhabited by the Coleopturies in the Orino Galaxy. It was destroyed prior to the Universal War in 3510 UB by Speccio as their leader Spec was unhappy with the planet's decision to reject their rule. The destruction of the planet nearly caused the Coleopturie species to go extinct and many didn't have a home to return to. Many fled to planet Bugroo.
Planet Oxu was a medium sized planet in the Ceros Galaxy in the Yuxas System. It was another planet that was also destroyed at the hands of Spec and Speccio, for the same reasons: the sovreigns of the planet refused to submit to Spec's rule. The inhabitants, knowing the fate of Beetledeo began to panic immediately after and many fled the planet before it was destroyed by Spec.
The Oxu population also nearly went extinct after the destruction, but even moreso since Oxu was a smaller sized planet compared to Beetledeo. Now, it's still rare to see an Oxu on or off planet. The destruction of Oxu also led planets to band together and fight back.