The Apocalyptic Mutant

This despicable creature comes from the 2514 Earth Apocalypse. -

Many creatures were "contaminated" by the Chora virus released by Aperture Corp. and two of the side effects were skin overgrowth and mind loss. The excessive skin lead to harden and for a protective "shell", much like the Earth creatures, crustaceans and the mind loss lead to them becoming highly cannibalistic and very hungry because of the need of food for growth.

The victims were sent into a vicious cycle of needing to feed or starve, because 98% of ingested food went on growth, yet another side effect of the deadly virus, and it caused them to become tougher to kill. And because of their cannibalistic nature, they often raided cities in large numbers for their feeding grounds, due to the high number of population.

There creatures were undoubtedly the downfall of the human race.