text: The luciferases of fireflies – of which there are over 2000 species – and of the other Elateroidea (click beetles and relatives in general) are diverse enough to be useful in molecular phylogeny.  In fireflies, the oxygen required is supplied through a tube in the abdomen called the abdominal trachea.  One well-studied luciferase is that of the Photinini firefly Photinus pyralis, which has an optimum pH of 7.8.