Octopuses & Squids: Support Your Local Cephalopod

Caribbean reef octopus
I believe this is a Caribbean reef octopus (Octopus briareus)

TO BE SURE, CELEBRATING OCTOPUSES, SQUIDS AND THEIR COUSINS DOESN’T NEED A SPECIAL DATE. But it’s Cephalopod Week, so here are some awesome cephalopod facts, by the numbers:  

1.   Cephalopods, best known by octopuses and squids, are remarkable for their braininess, and also their brains. Physically, their heads are often larger than their bodies, which perhaps explains why they’re very smart, as well. The term cephalopod is taken from the Greek for, literally, “head-feet.” Perhaps less familiar, at least in North America, are cuttlefish and nautiluses, other members of the cephalopod order.

2.   Octopuses tend to have a reputation as friendly, highly intelligent, inquisitive animals, sort of like Labrador retrievers. Also, as scamps. Tales of octopuses escaping from aquarium tanks and playing tricks on their human keepers are legendary. In New Zealand, one named Rambo learned to shoot photos of human visitors.

3.   In my experience, squids seem inquisitive as well, but more reserved, like cats. Actually, speaking as a dog person, I’ve had some of my best undersea communions with squid, several minutes of calmly contemplating each other above the reef. Or, perhaps, they’re just wondering I’m doing there.


4.  There are some 300 species of octopuses, about 300 species of squids, more than 120 species of cuttlefish and only a handful of nautiluses in the world’s oceans.

5.   Octopuses and squids are found around the world, in waters both tropical and arctic, at every depth. Cuttlefish are found in all the world’s oceans except along the east coast of North America and the Caribbean. The six species of nautiluses are confined today to the Indo-Pacific basin.

Common octopus (Octopus vulgaris)


6.   Cephalopods are famous for their multiple arms, equipped with muscle-controlled sucker-like discs that let them grip prey. Octopuses have eight arms, squids and cuttlefishes eight arms and two feeding tentacles, which are longer than the arms. A common octopus has some 240 suckers on each arm. The arms surround their (usually) only hard structure, a chitinous beak used to devour prey.

7.   Male nautiluses have as many as 90 arms, females around 50. Nautilus arms lack the suckers and strength of other cephalopods but make up for it with their multitude of limbs.

8.   Octopuses tend to swim head first, with their arms trailing behind them. Squids, cuttlefishes and nautiluses swim with their arms in front, even though this may look backwards. They all swim with the jet-propulsion created by funneling water through their bodies.

9.   That being said, octopuses are mostly bottom-dwelling animals and don’t swim that much and often prefer to locate in a protected den in a crevice or hole. Squids and cuttlefish hang out higher in the water column. Squids can jet around as fast as 25 miles-per-hour, but can keep up that pace only for short distances.

Caribbean reef squid
Caribbean reef squid (Sepioteuthis sepiodea)


10.   Cephalopods have highly developed nervous systems, which aid in their extraordinary senses of smell, vision, touch and instant color-control. Chemoreceptors at the end of each tentacle help them detect and acquire prey.

11.   Research has suggested that cells all over octopuses’ skin are light sensitive, essentially making their bodies “one big eye.” By exposing octopus skin that was pale in darkness to sudden light, scientists found it turned dark very quickly.

12. Their phenomenal abilities to change colors and camouflage enable them to disappear into nearly any background as a defensive measure. They do this by enlarging or shrinking color-changing, pigment-laden cells called chromatophores, located just below their skin’s surface. Some use other cells, as well, called iridophores and leucophores. Octopuses, at least, can also change the texture of their skin to better match their surroundings.

13.  Even though they can rapidly manipulate their colors, and even though their vision is excellent, all octopi and most other cephalopods are color-blind.

14.   All cephalopods are carnivores. Squids, cuttlefishes and nautiluses prey primarily on fishes. Staying at the sea floor, octopuses feed primarily on crustaceans, clams and other mollusks. A good clue that an octopus’s den is nearby is a pile of discarded clam shells near a crevice.


15.   Even though it’s fun the say octopi, it used to be that the only proper plural of octopus was “octopuses.” Today, etymologists have given up and “octopi” is grudgingly accepted as a viable word choice. The plural of squid, if you’re talking about more than one of the same type, appears to be… “squid,” as in “I encountered three squid swimming together.”  If you’re talking about multiple animals of differing species, it’s “squids,” as in “three types of squids.” Same thing with cuttlefish/cuttlefishes. But more than one nautilus get to be nautiluses, no matter what.

16.   They’re all mollusks, octopuses, squids and all, along with clams, oysters and scallops. Clams, oysters and scallops live in flattened bivalve shells, and conchs and other shelled snails sport cone-shaped shells. Except for nautiluses, cephalopods generally don’t have any external shells. Cuttlefish do retain small, internal remnants of shells, the “cuttlebone.” It may aid in buoyancy, and, sold in pet stores, also contributes to the well-being of parakeets.

ammonite fossil
This nautiloid fossil, dating back some 400 million years ago, is only about three inches long, but in their heyday ammonites reached lengths of as much as six feet. Their arms extended out the coiled shell’s opening at right. 

17.   Hundreds of millions of years ago, cephalopods ruled the world’s oceans in the form of ammonites and belemnites. Ammonites jetted along inside long, coiled shells, in some species as much as six feet in length. Belemnites sported cone-shaped shells. Some 160 to 100 million years ago, many cephalopods found that the agility and speed they acquired by shedding their shells outweighed the defensive advantages of carrying shells around.


18.  It’s the absence of any hard shells that enables octopi to exercise their phenomenal escape artist skills, squeezing their way though tiny holes and cracks.

19.   Nautiluses retained their chambered shells, which may be why there are only six species extant today. The shells’ interiors are constructed with a series of chambers that can be filled with air to control buoyancy. And, the animal itself can close off the entrance for protection.

20.   Squids, cuttlefishes and most octopuses are also renowned for their ink, a dark natural pigment they can eject to distract predators while they make an escape. Stored in an ink sac opening into the anus, it’s mixed with mucus to form a thick cloud as it’s expelled. Research has indicated that in some species the ink contains the chemical dopamine, which produces a sense of euphoria in humans.

A giant-cuttlefish (Sepia apama)
A giant-cuttlefish (Sepia apama)


21.   A different escape technique is used by the vampire squid (Vampyroteuthis infernalis), which is actually an octopus. Far from feeding on prey’s blood, infernalis bite off an end of one of its arms, which, being bioluminescent, distracts its predator as it flees.

22.   While some large octopuses may live for several years, most octopuses have relatively short lifespans, sometimes less than a year. Hormones that cause octopus reproductive organs to mature for reproduction close off their digestive glands, generally causing the octopus to starve. Males die in a matter of months following mating, females soon after their eggs hatch. First, however, the males are very protective of their mates’ eggs.


23.   Noted for their superb vision, octopus eyes resemble those of humans, and have been used in human eye research.

24.   Squid nerves that are especially thick are used to teach surgeons in training in the basics of neurosurgery.

25.   Geneticists are particularly interested in cephalopod evolution and have been studying octopus and squid DNA and RNA.

PRINCIPAL SOURCES: Marine Biology, Fourth Edition, Peter Castro, Michael Huber; Reef Creature Identification, Florida, Caribbean, Bahamas, Reef Creature Identification, Tropical Pacific, Paul Humann, Ned DeLoach; Marine Life, Caribbean, Bahamas, Florida, Marty Snyderman & Clay Wiseman; Common Octopus, Common Squid, et. al., MarineBio.orgIntroduction to Cephalopods, et al., The Cephalopod Page;  Molluscs of Australia, et al., Marine Education Society of Australasia; Cephalpodia, Animal Diversity Web, University of Michigan; Cephalopda, Tree of Life; How Octopuses and Squids Change Color, Smithsonian Institution; Cephalopod, Class of Mollusks, Encyclopedia Britannica;  Cephalopods, Octopus, et al., Wikipedia; Figuring Out Why and When Squids Lost Their Shells, New York Times; Fourteen Fun Facts About Squids, Octopuses and Other Cephalopods, Smithsonian.com.