Original: The bilateria are all animals having a bilateral symmetry , i.e. they have a front and a back end , as well as an upside and downside . Radially symmetrical animals like jellyfish have a topside and downside , but no front and back .
Simplified: Bilateria are all animals having a bilaterally symmetrical animals , they have front and a back end , as well as an upside and downside .