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[Anomalocaris]

Jupiter is about as large as any planet can get in normal circumstances.     Planets less massive than Jupiter would be physically smaller because they have less stuff.     Planets more massive than Jupiter would also be physically smaller because gravity from their added mass compressed their stuff so much that they actually take up less volume. 

The only planets that can get appreciably bigger than jupiters are gas giants locked in extremely close orbits about their stars.   The stars heat these planets so much that their atmosphere puffs out.