How are the scales of tetraodontiform fishes modified into plates or spines?

In tetraodontiform fishes, the body scales are highly modified to provide protection, evolving into various forms depending on the group. Rather than typical overlapping scales, these modifications include:1

• Plates: In triacanthoids and balistoids, the scales are modified into overlapping plates. In ostracioids (such as boxfishes), these plates become sutured together to form a rigid, turtlelike carapace or cuirass.12
• Spines: In tetraodontoids, the scales are modified into sharp, projecting spines. These may be small and erectile, as seen in puffer fishes, or large and either erectile or fixed, as observed in porcupine fishes.12

While these modifications represent a significant departure from the standard scales of other bony fishes, some members of the order, such as the ocean sunfishes, have moved toward a different strategy where the skin itself becomes exceptionally thick, leathery, and hardened by deep layers of connective tissue.12