Leviathans

The beasts of the deep and longs since been the reason for sobbing widows and entire shipping companies going under overnight.
They come in many sizes, as long as their size is worthy of the title of leviathan, as well as a non-standard form and temperament. Some of these creatures share their form with creatures like the whale and the octopus, of course being much larger than their more common doppelgangers. Others have their own form, unique amongst the beasts of the sea and never to be seen other than within that one creature and it's kin.
They are as varied in behavior as they are in appearance, with the creatures being equal parts docile and predatory. While those that are docile, or even imparted with a curiosity as begets a child, are an incredible sight to see, the devils amongst their ranks are more than enough to put the fear of leviathans into the heart of sailor and civilian alike. Creatures big enough to crush warships within jaws, tentacles, or whatever they may have, tend to place potential victims on edge.

Basic Information

Genetics and Reproduction

Where the creatures that are called Leviathans, especially those that don't have a familiar form, come from is another mystery to add to the pile. One could assume that the examples of exceedingly large whales or octopi are members of the species they appear as, simply larger. The others are far more difficult even to theorize when they exist in numbers so small that they become impossible to confirm if there are more than one individual to a particular species.
The idea that perhaps they just spontaneously spawn out in the deep ocean is ridiculous, but there is little evidence otherwise and the mental image such a concept inspires is both amusing and unsettling.

Technically, the title of "leviathan" is simply an umbrella term meant to capture the creatures that are large enough to have it applied to them.

Lifespan

unkown