Introduction to Cephalopods
Cephalopods, the class of mollusks which scientists classify octopuses, squid, cuttlefish and nautiluses, can change color faster than a chameleon. They can also change texture and body shape, and, and if those camouflage techniques don’t work, they can still”disappear” in a cloud of ink, which they use as a smoke-screen or decoy.
Cephalopods are also fascinating because they have three hearts that pump blue blood, they’re jet powered, and they’re found in all oceans of the world, from the tropics to the poles, the intertidal to the abyss.
Cephalopods have inspired legends and stories throughout history and are thought to be the most intelligent of invertebrates. Some can squeeze through the tiniest of cracks. They have eyes and other senses that rival those of humans.
The class Cephalopoda, which means “head foot”, are mollusks and therefore related to bivalves (scallops, oysters, clams), gastropods (snails and slugs), scaphopoda (tusk shells), and polyplacophorans (chitons). Some mollusks, such as bivalves, don’t even have a head, much less something large enough to be called a brain! Yet cephalopods have well-developed senses and large brains. Most mollusks are protected by a hard external shell and many of them are not very mobile. Although nautilus has an external shell, the trend in cephalopods is to internalize and reduce the shell. The shell in cuttlefish, is internal and is called the cuttlebone, which is sold in many pet shops to supply calcium to birds. Squid also have a reduced internal shell called a pen. Octopuses lack a shell altogether.
Cephalopods are found in all of the world’s oceans, from the warm water of the tropics to the near freezing water at the poles. They are found from the wave swept intertidal region to the dark, cold abyss. All species are marine, and with a few exceptions, they do not tolerate brackish water.
Octopuses or Octopi?
Many people get confused about the proper plural for the word octopus. Octopus is frequently given a Latin plural, yet the word derives its second root from Greek, not Latin (the english “foot” root from Latin is “pod” or “ped”, while from Greek it is “pus”). What is the proper plural, anyway? Many say “octopi.” The singular looks like a Latin masculine singular, ending in “us,” but it really isn’t, so pluralizing it to “octopi” is not correct. Most people also mispronounce it as well. If it were “octopi,” it would be pronounced “octo-pee” not “octo-pie,” and that sounds silly! So, the correct plural is “octopuses,” believe it or not. Some prefer not to use either of them, as every time you say “octopuses” someone will correct you, and you end up in an argument. So a simple way around this is to use “octopods,” which is the proper plural of the taxonomic order Octopoda, containing the eight-armed cephalopods.