CreditCreditFred Tanneau/Agence France-Presse — Getty Images

The octopus is an invertebrate (spineless creature) and belongs to the Cephalopod family. The amazing Smithsonian Ocean Portal provides a family tree as well lots of other fascinating information about cephalopods:

The cephalopods are a diverse class of mollusks. Today, scientists divide the living cephalopods into three groups, called superorders. Many details of cephalopod evolutionary classification continue to change as scientists find new clues from genetic testing and newly discovered fossils. (Created by Ashley Gallagher for the Ocean Portal)

Cephalopods have been around for a VERY long time and have been among the dominant large predators in the ocean before they became every animals favorite dish. The Earth Archives provides a good look at...

500 Million Years of Cephalopod Fossils

Animalogic provides a good introduction to the octopus as well as explaining what makes them...

The World’s Greatest Escape Artists

10 reasons why the octopus is one of the most incredible creatures in the sea:

The National Aquarium provides this helpful infographic:

The octopus makes a good mother as reported by Pang Quong: In Port Phillip Bay during October, one of our small octopus(Octopus pallidus) lay their eggs in small caves ,bottle or old tyres. The female stays with her eggs until they all hatch. Over about 3 weeks I checked the progress of one female and her eggs:

It was long assumed that the octopus was a solitary, antisocial creature, until the recent discovery of two octopus "cities": Octlantis and Octopolis:

Octlantis is a just-discovered underwater city engineered by octopuses

The gloomy octopus, lonely no more in Octlantis.

Why octopuses are building small “cities” off the coast of Australia

A map of Octlantis, the second settlement of gloomy octopuses found off the coast of Australia. About 10 to 15 octopuses live here, in mounds of shells that have been constructed over generations.

'Octlantis': Bustling Octopus Community Discovered Off Australia

One of the most comprehensive web pages on the octopus can be found at ourmarinespecies.com:

Octopuses: Characteristics, habitats, reproduction and more

The Daily Catch: An Octopus has 3 Hearts, 9 Brains & Blue Blood

The nine brains of the octopus all add up to a considerable intelligence:

New York Times: Yes, the Octopus Is Smart as Heck. But Why?

Coconut Carrying Octopus

Scientific American: The Mind of an Octopus

Credit: HENRIK SORENSEN Getty Images

The New Yorker: Why Not Eat Octopus?

And one (or rather eight!) of the most fascinating things about the octopus: their tentacles, each one of which has its own mini-brain!