Italian crested newt
When newts are inactive or in oxygen-rich environments, respiration can be done through their skin which accounts for 74% of the cutaneous respiration. However, oxygen-poor environments, such as stagnant ponds, pose a threat to the survival of larval newts. This is because oxygen molecules do not readily dissolve in water, and as "T. carnifex" is an immobile animal, extracting oxygen from water is difficult. Newts consequently have external gills at birth that persist until metamorphosis, which assists survival in low-oxygen conditions.
Iberian ribbed newt
The Iberian ribbed newt has tubercles running down each side. Through these, its sharp ribs can puncture. The ribs act as a defense mechanism, causing little harm to the newt. This mechanism could be considered as a primitive and rudimentary system of envenomation, but is completely harmless to humans. At the same time as pushing its ribs out the newt begins to secrete poison from special glands on its body. The poison coated ribs create a highly effective stinging mechanism, injecting toxins through the thin skin in predator’s mouths. The newt’s effective immune system and collagen coated ribs mean the pierced skin quickly regrows without infection.