the translucent skin of the northern glassfrog (hyalinobatrachium fleischmanni) allows us to see its internal viscera, and, in the case of the fifth photo, a mother’s eggs.
and yet, it is the male glassfrogs who alone provide the parental care, as the females flee the scene once the eggs have been delivered. it for this reason that these protective male glassfrogs can be extremely aggressive.
to date, there is no clear explanation for the evolution of this transparency. most frogs are not transparent, as this would expose organs to the deleterious effects of sunlight and heat.
but the transparent underbelly of the glassfrog is covered in light reflecting organelles called iridiphores which could give the glassfrogs the ability to optimize their internal homeostasis.
some suspect this abdoninal transparency helps the glassfrog to blend into its environment, though no evidence as yet supports this crypsis hypothesis.