Are you ready to celebrate? June 21-28 is Cephalopod Week. So exciting! No, we don’t get to take the week off from work, and it’s not a real holiday, but it is a way to raise awareness about and celebrate octopi, squid, cuttlefish and nautiluses. This year, Cephalopod Week, created by NPR’s Science Friday, will celebrate its sixth year running.
Taxonomically, cephalopods are a kind of mollusc and therefore closely related to clams, oysters and snails. Cephalopods live throughout the world’s oceans, from surface waters to depths of more than 4 miles. The name “cephalopod” means “head-foot,” which refers to the fact that their limbs are attached to their head.
Why celebrate cephalopods? They’re cool, that’s why!
Cephalopods are undoubtedly the most intelligent, most mobile, and the largest of all mollusks, and their evolutionary history spans a good 500 million years. There are about 17,000 named species of fossil cephalopods, and about 800 identified living species today. The largest is the giant squid, which measures up to 60 feet long. The smallest is the pygmy squid, which measures just a half-inch long.
Cephalopods are brainy. That’s right — with a centralized brain, the largest of all invertebrates they possess the ability to remember and learn by example, or through trial and error. It’s hard to quantify exactly how smart they are, but some squid are known to communicate complex messages with others of their species by use of color, and octopus are notorious for carefully dismantling things in captive settings.
Equally fascinating, a cephalopod’s eye is probably the most sophisticated of all invertebrates. Their large eyes contain an iris, pupil, and lens, and sometimes a cornea.
Octopuses, cuttlefish and squid have eight arms. These arms often have suckers, and sometimes they have hooks along their undersides; they use these to catch prey. Cuttlefish and squid also have tentacles. Tentacles are longer than arms, and are retractable. Tentacle tips are blade-shaped or flattened, and covered in suckers. Squid and cuttlefish each have one pair of tentacles which they use to strike or capture prey.
Cephalopods can walk or crawl using their arms, or they can fly through the water using jet propulsion. Jet propulsion is accomplished by expanding or contracting their fleshy body covering, called the mantle. As they expand their muscular mantle, water is drawn in, and as they rapidly contract, a jet of water enables the animal to quickly move backwards and forwards through the water.
Cephalopods have an amazing ability to change color very rapidly. They accomplish this feat using numerous pigment-filled bags, called chromatophores. As mentioned earlier, some use this ability to communicate. Others are more focused on camouflage. Some octopus species take this ability to another level, changing their body shape and even skin texture to resemble rock, coral or sometimes other animals.
Sex and reproduction in cephalopods is very different from other mollusks. There is both a male and female, and mating usually includes a courtship that often involves elaborate color changes. This is followed by the transfer of a sperm packet from male to female. Most females then lay eggs. Male and female adults die shortly after spawning.
Although many cephalopods reach large sizes, generally they have very short life spans. Their life expectancy is only a year or two for most species. It is thought that this short life history may be a strategy that helps them to rapidly increase their population size, and in turn may help to guarantee survival during environmentally stressful conditions, including those caused by heavy predation or overfishing. Because their generation gap is so short, dying young also allows cephalopods to evolve rapidly.
So there you have it — cephalopods in a nut shell (did I mention that some octopus will collect discarded coconut shell halves to build shelters?). If you have fun celebrating cephalopods in June, guess what? You can do it all over again in October during Cephalopod Awareness Days. That’s right: There’s not one but two non-holiday holidays for these special invertebrates!