Chapter Six: The Biology of Squid, Giant and Otherwise: Introducing the Teuthids, a Group of Fascinating Decapod Invertebrates that Range the World’s Oceans – Lighting up, Changing Color, and even Leaping from the Water.

Chapter six was when I REALLY started paying attention to what Ellis was saying. Did you know that the word “squid” is both plural and singular? I did not – which just goes to show how embarrassingly little I knew about squids before reading this book!

The giant squid does in fact exist – and has a raspy tongue (called a radula) inside its beak that is covered in tiny teeth! Instead of hemoglobin, squid have hemocyanin, which means “blue blood.” The vision of a squid is twice as good as the vision of a human. For someone (like me) with a -6.0 prescription, this facet of a squid’s biology was particularly intriguing. Even more impressive is the squid’s ability to change color instantly and at will. One of the instances in which this skill is used is when two male squid engage in a “color duel” to attract a mate. That sure would attract my attention! So does this amazing creature have any weak points? Yes: it turns out that squid cannot make a sound (according to popular scientific belief).

Some squid can also light up (and I’m not talking about smoking a joint). A megalocranchia is a transparent squid with photophores on its liver. Other species of squid have these light-up organs on their eyes or gonads. Luminescence is still poorly understood by today’s scientists.

Another species of squid, referred to as a “flying squid,” can actually shoot out of the water like a rocket. According to Ellis, this species of squid has even been known to “fly” in formation. This chapter provides an interesting example:

“When Thor Heyerdahl and his companions were sailing the Kon-Tiki across the Pacific in 1947, they first thought that squid had come on deck by climbing aboard the raft, but when they found one on the thatched roof of the deckhouse, they began to wonder. Finally, the mystery was solved: One sunny morning we all saw a glittering shoal of something which shot out of the water and flew through the air like large rain drops, while the sea boiled with pursuing dolphins. At first we took it for a shoal of flying fish, for we had already had three different kinds of these on board. But when they came near, and some of them sailed over the raft at a height of four or five feet, one ran straight into Bengt’s chest and fell slap on deck. It was a small squid. Our astonishment was great” (Ellis 179).

I found another interesting quote in this chapter, and it reminded me of Zoidberg (who is more squid than human) because there is an episode of Futurama that mentions the fact that if Zoidberg has sex, he will die. “After the frenzied copulation and egg laying, the squid are substantially weakened, and those that do not die outright are easy prey for the sea lions, sharks, and dolphins that hungrily attend the annual spawning. While many invertebrates pass through  a larval stage, squids hatch as miniature adults, capable of escaping and feeding” (Ellis 181).

Now for something a little more serious: this book taught me that the study of squid has revolutionized the study of neurophysiology in humans. Squid have unusually large nerve fibers. These fibers can be as large as 0.1″ in diameter, whereas the largest human axon is only .001″ in diameter. These giant axons enable squid to transmit messages faster than any other creature and to instantaneously respond to stimuli.

Fun Fact: Most scientists believe that squid are among the most numerous animals in the world.

Fun Fact: The most dangerous squid in the world is the Humboldt squid; click here to see a picture.

Some interesting words from this chapter:

“Hectocotylus” – meaning “one hundred suckers,” this word has an interesting history. Originally thought by Baron Cuvier to be a parasitic worm, it was eventually discovered to be the sex organ of the tiny male argonaut (the organ breaks off after fertilization). “The male himself is only an inch long compared to the females’ 18-inch bulk (including tentacles), and he consists almost entirely of reproductive organs; he has no heart, does not eat or breathe, and is often carried around in the shell of the female” (Ellis 180). So basically, a hectocotylus is living squid-penis.

“Cephalopod” – any mollusk of the class Cephalopoda, having tentacles attached to the head, including the cuttlefish, squid, and octopus.

“Mesopelagic Zone” – a layer of the oceanic zone generally between 200 and 1,000 m (656 and 3,280 ft). The mesopelagic zone receives very little sunlight and is home to many bioluminescent organisms.

“Bathypelagic Zone” – a layer of the oceanic zone generally between about 1,000 and 4,000 m (3,280-13,120 ft). The bathypelagic zone receives no sunlight and water pressure is considerable.