Terrorclaws

An encounter with a Terrorclaw is an absolute nightmare scenario for any mariner, no matter their level of experience. They are most closely related to crustaceans, but researchers find that each one behaves more as a colony than an individual organism. Being a conglomerate of smaller organisms, there has been no defined limit to how large a Terrorclaw can get. It was believed that like the Kaiser Shark, the Terrorclaw was a bi-product of human pollution and activity in the South Harbinger Sea, but there have been accounts and sightings prior to these events. Smaller Terrorclaws (50ft in diameter and below) will resemble something of a massive lobster-like creature, with a deep, midnight-blue hue. Like its name implies, it has an enormous pincer claw, the subject of terror for many a sailor. 
The largest Terrorclaw (Cancrius Rex) ever recorded was in Y3156, being 126.5 miles at its longest point. At this stage the Terrorclaw has reached its "Island Eating" phase, where it will induce local but intense tremors, causing episodes of rapid liquefaction in nearby islands. It will then proceed to "eat" the island by consuming the soil (and everything on it) to filter it for nutrients and other beneficial substances. This particular Terrorclaw singlehandedly removed a slew of coastal islands from the map of the Primus Territory before it was stopped in Y3159. Johannes Altig, General of the Collingian Coastal Defense Force, ordered 1.15 million barrels of a cinderite-laced sulfite solution to be dumped onto the coast so as to surround the beast. this deluge of material was then ignited, immolating the entire coast and starving the Terrorclaw of its food supply. To this day the area has never fully recovered from the devastation, and this 16,000 sq mi area is now known as O'Boyle Swamp.