3 day old embryos of red-eyed treefrog. They have external gills that protrude toward the surface of their eggs, where oxygen is most concentrated. This adaptation allows for high metabolic rates and accelerated development
Cymothoa exigua, or the tongue-eating louse.The parasite severs the blood vessels in the fish's tongue, causing the tongue to fall off. It then attaches itself to the stub of what was once its tongue and becomes the fish's new tongue.