Underbellies are the soft and vulnerable parts of an organism that are usually hidden from view. Antonyms for the word "underbellies" include strong, armored, resilient, and impenetrable. Instead of being soft and susceptible to damage, these words suggest durability and toughness. Antonyms for underbellies also include exposed, available, and accessible, indicating that these parts are easily visible or open to attack. By using these antonyms, one can describe the opposite of an underbelly, conveying the idea of something that is resilient, protected, or readily visible. Ultimately, selecting the right antonym will depend on the context and the message one is attempting to convey.