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The animal on the cover of Ethernet: The Definitive Guide is an octopus. The octopus is a member of the class Cephalopoda, which also includes squid, cuttlefish, and nautili. However, unlike other cephalopods, the octopus’s shell is entirely absent. Species of octopus vary in size from under an inch (the Californian Enteroctopus micropyrsus) to 30 feet in length (the Giant Pacific Octopus dofleini). Like its cousin the squid, the octopus can release a noxious ink when disturbed. Octopodes vary in color from pink to brown, but are able to change their skin’s complexion when threatened using special pigment cells called chromatophores.

Octopodes catch their prey—primarily crabs, lobsters, and other smaller sea creatures—with their suckered tentacles. Many species are aided by a poison these sucker cups secrete; the venom of one Australian species is so potent that it can be deadly to humans.

Octopodes are considered the most intelligent invertebrate species. They have both short- and long-term memory and have shown trial-and-error learning skills, retaining the problem-solving capabilities gained through experience. Their sucker cups are very sensitive; a sightless octopus can differentiate between various shapes and sizes of objects just as well as a sighted one.

The cover image is a 19th-century engraving from the Dover Pictorial Archive. The cover fonts are URW Typewriter and Guardian Sans. The text font is Adobe Minion Pro; the heading font is Adobe Myriad Condensed; and ...

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