Icehog

Replacing its ancestor, the Emperor Seaswimmer, in the North Sagan 4 Ice Sheet, the Icehog's unique traits were driven by the intense competition for food with the scylarians. Evolving a purely white coloration matching that of the polar ice, it not only gained an upper hand against them—as the species grew bigger, it has come to eat the competition as a primary food source. Inheriting the ambush tactics of its ancestor, the Icehog lies low in wait near masses of ice for scylarians or the Vicious Seaswimmer to pass by before quickly rising up, capturing them unawares. As a more fusiform body, powered by a hypocercal caudal fin, rushes towards the quarry, stabilizing it in this pursuit is a pair of large canine teeth that project to the side, rudimentarily acting as fins. As these teeth angle downward from their upper jaw, they also function in restraining and wounding the prey item as it's being held in the mouth.

It retains monogamy from its ancestor. Taking advantage of the vibration-sensitive fatty bulge in their lower jaw, mated pairs establish their territory with low-rumbling calls that aren't so much heard as they are felt. Unpaired females make slightly higher-frequency rumbles to attract males. Predictably, there will be a lot of takers. To compete for the female, males aggressively rumble at each other, with the meeker ones usually backing down. The bolder ones, however, will try to gash their obstinate opponents with their front tooth. This will leave scars, but they are never life-threatening due to this species' thick blubber. In fact, larger males can bear numerous scars, a testament to their endurance as they simply wait out their smaller, younger rivals' aggression until they become exhausted and swim away.

It gives birth to fewer offspring, maximally up to two at a time (and, in rare cases, three). However, not only are they larger than the Emperor Seaswimmer's, they strike out on their own, aided by their white coloration blending in with the ice, being harder to detect by either predator or prey.

Becoming further adapted for its frigid domain, it is now an true homeotherm, maintaining a constantly warm body temperature, which is insulated by the thick layer of blubber inherited from its ancestor. This metabolic enhancement, further bolstered by the atmospheric oxygen it breathes, gives it a greater advantage over its prey, being able to move faster despite the cold polar water of its habitat.