Incredibly simple organisms, yet fascinating to watch, squid are cephalopods; close relatives of octopus, cuttlefish, and nautilus. These members of the Teuthida order, which includes two suborders, comprise the largest cephalopod order, with approximately 300 known species. Interestingly, new technology is enabling researchers to discover new species; and, even better, we are learning more about squid all the time. Usually having ten legs and a streamlined shape, these animals have inspired myths and legends throughout recorded history. In many places, they are fished for culinary use. Whether you enjoy consuming calamari or not, you’re certain to enjoy a closer look at some of the more commonly encountered species.
Squid Basics
As with many other creatures, squids have ancestors in the mollusk family. What once may have been the mollusk’s foot has been modified into a much more complex set of tentacles and well developed sensory organs. Highly intelligent for the most part, and equipped with advanced eyes similar to those found in most vertebrates, squid differ from octopuses in several ways; one of the most remarkable differences is that they have an internal gladius, or pen, which is the vestiges of the ancestral shell. Shaped like a feather, this structure is a very basic internal skeleton composed of a chitinous substance. It serves as a structure for muscle attachment and supports the squid’s mantle, preventing it from motion as fluid as that which octopuses are capable of.
Equipped with swimming fins and covered in chromatophores which enable it to change colors and textures to blend in with its surroundings and to communicate with one another, squid normally have a light colored ventral side and a darker colored dorsal side which aids it in avoiding capture by predators. Its main form of locomotion is jet propulsion, in which water is sucked into the mantle cavity and expelled through an organ called the siphon. Squid are capable of precise motion and can travel at high speeds; this agility paired with their incredible displays makes them fun to watch. They shoot themselves backward, tails first, sometimes moving as fast as 25 body lengths per second.
Reproducing via internal fertilization methods rather than spawning, most squid live for about a year, with both male and female dying after mating. Female squid hide clusters of gelatinous eggs beneath rocks, and juveniles hatch as miniature replicas of their parents. Tiny juvenile squid graze on plankton while growing to adulthood; after that, they consume a variety of shellfish, crabs, and finned fish. Adults are stealthy hunters, often stalking their desired prey then hiding out of sight, waiting for victims to come close enough to snatch. Equipped with a sharp, parrot-like beak, squid eat quickly, gulping their food after it is ground up by sharp radula on the tongue.
Interestingly, squid are becoming more numerous as global water temperatures rise, and they are growing to larger sizes, creating a fisheries boom, particularly around New Zealand and Australia. An extremely sustainable population capable of replacing itself annually and not living long enough in most cases to accumulate high levels of toxins, squid are not only fascinating animals, they are a very good seafood choice for those who consume animal proteins. Normally fished via purse seining after being lured close to the surface with lights, squid are carefully captured right on top of mating and breeding grounds after they have laid their eggs, just prior to their natural deaths. This abundant species is not only a favorite human food, it is also an important source of nourishment to many fish, sharks, and other marine life.
Common Types of Squid
Depending upon where you dive, you may encounter different varieties of squid. Here are some of the most commonly encountered squid species.
Market Squid, or Loligo opalescens, can be found in shallow water all along the eastern Pacific seaboard, from Alaska all the way south to Mexico. Plentiful in the Channel Islands and in Monterey Bay, these squid grow to no longer than a foot long and have a mixed iridescent coloration ranging from white to purple. Whenever masses of these squid gather, so do seals, sea lions, and big pelagic fish, which prey on them.
Common European Squid are found in the Eastern Atlantic Ocean and in the Mediterranean Sea. Usually living in depths between 20 and 500 meters, they grow to be about 16 inches long and have a white color with a bronze to brown spotted pattern. Like Market Squid, this abundant species is carefully managed and fished commercially.
Shortfin Squid live in the Atlantic Ocean and are found all the way from Newfoundland, Canada, to Florida. A migratory species that travel south to lay eggs in warm water, it is closely related to the Argentinian Shortfin Squid. Both species serve as an important source of food for a number of other species, and both species are subject to fishing. Light brown to bronze, and sometimes taking on an almost eggplant-colored hue with an iridescent gleam, these squid can be found all the way from the surface to about 800 meters deep, though they seem to prefer to inhabit depths between 100 and 150 feet.
Humboldt Squid, which are also known as Red Devils or Diablo Rojo, Flying Squid, or Jumbo Squid, inhabit deep water during the day, coming all the way up to the surface to feed between dusk and dawn. Inhabiting the eastern Pacific and occasionally schooling in Puget Sound, this large species tends to swim in shoals that can number more than 1,000 individuals. If you plan to dive anywhere near this species, use caution. They are attracted to flashes and want to investigate anything that gleams; they have been known to go after divers and they even prey on sharks. Huge, with mantles up to six feet long and tentacles to match, this species is predatory and is merciless with its prey. Each sucker is equipped with razorlike teeth, and the animal’s beak is sharp enough to tear neoprene and flesh. Photographer Scott Cassell, who dives with and studies the species, has developed body armor for divers who want to get an up-close and personal look.
These are just some of the squid you may encounter while diving; you’ll probably never encounter others, such as the bioluminescent Vampire Squid and the Giant Squid, which has been documented at lengths of over 20 meters and which inhabits all the world’s deep oceans, are found well beyond recreational diving depths beginning at 200 to 300 meters deep. Still, keep your eyes open and your camera ready; depending upon where and when you dive, you could have an amazing squid encounter.