Egg of The Devourer

This creature develops in a bone lattice-reinforced egg too large for its mother to lay. Once the hatchling emerges after eating the rest of its brothers and sisters in the womb, it will proceed to consume the mother in her entirety. The mother's body constitutes a perfect environment to grow in, with acidic blood resisting decay and thick hide insulating from the elements. The hatchling also emerges with gills adapted to extract oxygen from the mother's blood, eventually shedding them for lungs once it eats a large enough cavity in the body for air to circulate.

Its teeth and jaws are specialized to tear flesh and crush bone with ease, its intense stomach acids digesting them quickly and efficiently. This reinforces its extreme bone density and musculature as it rapidly grows to full size in a few short months. It is arguably the most dangerous in these early stages- sporting a ravenous appetite and speed that belies its rotund appearance, and any being unfortunate enough to encounter it is almost certain to end up as a tasty snack for the hungry hatchling.

An early idea had it using a long stretchy tongue to snag prey, but I scrapped that for a powerful lunge that I feel better fits its aggressive nature.