Octopus (章魚), a class Cephalopod of the order Octopoda, is a boneless invertebrate characterized by eight arms with suction cups, a large head, and a beak-like mouth that is the only solid part of its body.
Squid (魷魚), a class Cephalopod of the order Teuthida, has eight arms but also scores two large tentacles. A squid also uses a beak-like mouth to feed and can eject a smoke of black ink to protect itself, similar to an octopus.
Cuttlefish (墨魚, 花枝, 烏賊), a class Cephalopod of the order Sepiida, is similar to squid in body structure but are generally smaller and carries internal shell.
So what is the kraken (in Pirates of the Carribeans)?
From above description, we can conclude that the kraken belongs to neither of the three orders. It has eight arms and 2 tentacles, so that comes from the squid; it has a soft, boneless structure similar to octopus; and its toothy, maw-like mouth comes from that sand beast at the beginning of Return of the Jedi .
Octopus are perhaps the most intelligent of all invertebrate. Study shows that they are capable of solving complex puzzles, retain both short-term and long-term memories, and when kept as pet can often break out of the aquarium by practice and gile.
In terms of size, the biggest known giant octopus weighted about 600 pouds, and has arms that averaged 5 meters. The largest giant squid currently known is 8.56 meters long, and is currently been preserved in the Natural History Museum in London.
And that concludes it, thank you all staying through this!
