Krakens

Calamarius immensum draki

Krakens were said to come from the flesh of Hades. This however, is not true. The first Kraken came from Oceanus. It served as a gift to Davy Jones (from Oceanus) as a reward for assisting him in his adventures. Krakens are sworn enemies of Sea Serpents.

Habitat
The deep depths of the world's oceans

Diet
whales and other large sea creatures.

Behavior
They are very aggresive and dont hesitate.

Biology
They have basically the same biology as a squid or octopus. No bones, smart etc...

Appearance
They appear to be a cross between an octopus and a squid but is insainly big. They can reach up to 200 ft long. 100 ft body and 100 ft legs

Tips for demigods
As a forewarning, being related to posidon won't help you keep it from killing you, so don't rely on relationships.

A flame based weapon is unadvisable. However Black powder weapons and lazers are very effetive. But the best way to kill it is to use the severed head of a medusa.