Giant Crustacean

Giant Crustacean was a monster from the New World that appeared in Mass for the Dead.

Appearance
A giant crab with a white translucent shell that shone brightly. It was apparently quite large, able to fill a cave passage.

Abilities
The creature grew in size due to continuous undisturbed molting over time. According to Solution Epsilon, it's shell was elastic and looked quite new, indicating it may have recently molted. It was nocturnal, and emerged from the cave at night, and may have been over two hundred years old as it was used by pirates as a living door for their hideout.

Trivia

 * The creature did not actually make an appearance, though it is killed off screen in the game by the Pleiades. It was blocking a passage to a hidden pirate hideout on a deserted island.