Minecraft wiki entry for Parity_issue_list, associated text: Wither skeleton/stray spider jockeys.
Spider jockeys riding cave spiders.
Baby husks/zombies can ride many mobs other than just chickens[feedback 31]:
Adult husks/zombies.
Cave spiders and spiders.
Most animals: cows, donkeys, foxes, horses, llamas, mooshrooms, mules, sheep, ocelots, pandas, pigs, stray cats and untamed wolves.
Skeleton horses.
Zombie horses.[note 6]
Zombie villagers.
Zombified piglins.