Thursday, June 05, 2014

8 arms and no legs

kw: book reviews, nonfiction, natural history, octopuses

Invertebrates in general spend nearly their whole lives growing up, mate once, and die. This is true even for the most intelligent invertebrate, the octopus. Particularly for octopuses: after mating, they go downhill rapidly. The male will die very soon, while the female will lay dozens to myriads of eggs and care for them until they hatch; during this time she fasts and loses as much as half her body mass. Then she dies within days. Think about that the next time you have an octopus dish. A healthy near-adult octopus is one who has yet to reproduce. Few live more than two years, and most live less than a year, from being an egg to producing eggs.

About the first third of Octopus! The Most Mysterious Creature in the Sea by Katherine Harmon Courage relates to their edibility. A few recipes are proffered. The Japanese, which call the animal tako (pronounced the same as "taco"), serve bits of octopus arm in sushi, but have the sense to cook it. Some cultures serve octopus raw, which is a great way to pick up parasites. But the only way the Korean "crawling arm" salad can be served is raw. The short chunks of arm have their own nerves and ganglia and know how to grasp and wriggle about, long after being severed.

As we read in the "Brain Power" chapter, even the suckers have ganglia and can perform tasks we'd usually associate with fingers of a hand, with little feedback from the central brain. We think of "the brain" as a location in which all the smarts reside. Yet our knee-jerk and other reflexes demonstrate that certain actions can be taken without any input from "command central". For an octopus, perhaps half or more of their real brain is distributed throughout the body. Thus, the published Encephalization Quotient (EQ) of around 0.04 is too low by at least half.

I long thought that the plural of octopus was octopi, then learned that the proper Greek plural is octopodes. However, Ms Courage states that the proper plural is octopuses (The lack of a red squiggly from Google when I type that last term indicates that they agree). The word has become fully Anglicized.

Octopuses come in all sizes. This Giant Pacific Octopus is being introduced to school children in Seattle. I saw one at Marineland of the Pacific when they were still in operation, that was about as big as they get, with arms 10 feet long, so that it nearly filled a tank window that was 24 feet across. This species is either the largest or second largest; scholars are still debating over it.

This picture shows the smallest (so far) known octopus species. It doesn't have a common name. This is an adult with arms less than an inch long (about 2 cm). In between, the Common Octopus reaches a weight of 3-4 kg with arms that are half a meter or so when relaxed, but can double in length when the creature reaches for something.

A fascinating aspect of octopus arms is that the nerves run in a loose channel and are arranged in zig-zag form when the arm is relaxed. Nerve tissue cannot stretch, so this allows the arm to reach without damaging the nerves.

The only hard part of an octopus is the beak, which is rather small. Many, and perhaps all, octopuses have a venomous bite. The four species of Blue-Ringed Octopus have the most dangerous bite known for any creature. This specimen is shown a little larger than life size. The body is smaller than a golf ball. But it carries enough venom to kill several humans. The venom is ordinarily used to immobilize prey.

The small beak in an otherwise wholly flexible, nearly fluid, body means an octopus can crawl through a surprisingly small opening. Even the eyes and the brain, which is ring-shaped and surrounds the esophagus, are flexible so that a grown Common Octopus weighing 3kg can get through a hole about 1cm in diameter.

While the book contains many facts of the natural history of these cephalopods, I wouldn't call it a natural history text. It is more of a romp through many interesting facts about these creatures, with quite a focus on various ways they are caught and consumed. Perhaps it is not so surprising that octopuses are extra-smart for being related to slugs. They are both predator and prey. They have two kinds of critters to outwit, those that they eat (crabs are a favorite) and those that want to eat them (including us). Octopus! is quite a fun read. While the author enjoyed quite a variety of Octo-cuisine during her research, I pass on it. I've eaten some, and they do taste good. But a critter that can look you in the eye in a way no other animal below your dog or cat can do, really doesn't belong on my plate.

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