This is the Balena.
She–because this is a strictly female monster–is an enormous fish. She is, in fact, one of the animals seen on maps accompanied by the words “Here be monsters.” If the name sounds familiar, that’s because science used it to designate baleen whales, among which are the largest creatures to ever exist on earth. It’s also the Latin name for “whale.” The balena, like her mundane cousins, is enormous. European sailors were in danger from this creature both because the mouth is large enough to tear apart ships and because of its habit of spewing huge amounts of water from itself, both from the mouth and the jets in the creature’s head. The mouth is so large, in fact, that in bad weather or in the face of danger she is able to hide her young inside it until she judges it safe, behavior seen in some real fishes. Balena give live birth and are known to sleep, although her male counterpart, the musculus, is said to come from eggs.
The balena is very buoyant, and as a result not terribly nimble. According to some sources, she floats at the surface of the ocean when in distress. She is also highly vulnerable to attacks from creatures like the orchun, which is said to first tear open the balena‘s belly, from which she cannot defend herself, and then throw rocks at her as she sinks to the ocean floor. The name of this beast is similar to the orca or killer whale, which is known to prey upon large whales, although there is very little known about the creature and no visual information to make this certain. For a large creature, the balena is also remarkably short-lived. According to one source, she only lives for ten years.