👉 Nine-spine is a type of spine in some animals that has two interchanged vertebrae, with the first being longer than the second. This structure is found in several species of fish and crustaceans. Nine-spine vertebrates include some very small, eel-like creatures, such as the nine-spined porcupine (Sarcoptes agilis) and the nine-spined pufferfish (Pomacentrus tenchii).
