The greatfin paralixo evolved from a population of Paralixo that migrated into Darwin Polar Coast. The cold, dark waters forced the paralixo to undergo changes, with the result being the greatfin paralixo.
The greatfin paralixo has developed three adaptations that allow them to survive in their new home. They have generally become darker than their ancestor, allowing them to trap heat with greater ease. They also have developed the ability to burrow. This is done with their hypertrophied upper tentacles, whose tips are reinforced with shovel-like cartilaginous elements. Their pectoral and pelvic fins also contain cartilaginous elements similar to those in the upper tentacles, allowing them to push excavated soil behind them while burrowing. When the dark winter arrives, the amount of food they have access to will drop immensely. As a result, the greatfin paralixo will hibernate in their burrows until the spring arrives.
The greatfin paralixo gets its name from its enlarged dorsal fins, which are attractive to females. These fins also contain cartilaginous elements. However, they are thinner and sharper than those located in the pectoral fins, pelvic fins, and upper tentacles. These elements provide attachment points for muscles that control the fins, which will pull them down when the greatfin paralixo enters its burrow. These spiky elements will also cause pain to predators as these elements may puncture the walls of the stomach, resulting in internal hemorrhaging. This dissuades predators from consuming more greatfin paralixos if they survive the ordeal. The greatfin paralixo's bioluminescent patches are located on the fins, and are used in communication and mating displays. These lights come in various shades of blue, and can vary between individuals. Males will attempt to attract females by raising and lowering its dorsal fins while rhythmically blinking its lights on and off.
Greatfin paralixos generally feed on small prey items like the even lesser knightworm and cleanupsticker. It will consume prey by shoveling them into its mouth with its lower tentacles. Its lower tentacles are tipped with hooked bony elements, which allow them to tear up large carcasses and move the resulting chunks into the mouth. Younger individuals will use the same behavior to tear apart and consume their prey.
The greatfin paralixo has also developed a notochord, which provides an attachment point for myomeres, which allow it to swim with greater ease than their ancestor. While they do spend much of their time 'walking' on the sea floor, this new swimming ability allows them to travel greater distances in search for food. As a result, the greatfin paralixo will swim when searching for new foraging grounds and mates, and walk when engaging in courtship practices, navigating their burrows, or hunting.