1. Exoskeleton: Insects developed a tough, external skeleton made of chitin. This exoskeleton provides protection from predators and physical damage, helps conserve water, and provides a rigid structure for muscle attachment, allowing for efficient movement.
2. Tracheal System: Insects evolved a specialized respiratory system called the tracheal system. This network of internal tubes brings oxygen directly to their cells, eliminating the need for gills and allowing them to breathe air efficiently in terrestrial environments.