Bunker Crab

Bunker Crabs are a fascinating species of large shellfish that can be found throughout the Southeastern waters of the Primus Territory. Its defining characteristics are its large, bulbous shell that has only a small slit opening at the front. They are bottom feeders by nature, but do contain razor-sharp claws underneath their large shells that are used to anchor themselves in strong currents or to break up larger prey. These crabs can grow as big as 4ft in diameter, and their shells were sometimes used as shields and makeshift defenses during the earlier times of Havanite expansion. 
The shell consists of a chitinous slab impregnated with particles of Aegis Aggregate, a naturally occurring regenerative concrete-like material. This regenerative matrix makes the Bunker Crab extremely durable, being able to withstand bites and attacks from predators far above their weight class. During mating season, groups of bunker crabs will dig a massive ditch on the ocean floor before laying their fertilized eggs inside. They will then climb on top of each other creating a solid phalanx dome over the ditch, protecting the gestating spawn. Over the course of a few days, the crabs in the phalanx will die and their bodies will petrify into a rock hard material, completely impenetrable from the outside. 1-2 years later the mass of eggs will hatch, revealing a new, larger brood.