Killer Sharks and the Tiger Shark

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Animal Phyla

Introduction

A 1600 Work I

Phylum Chordata I

Bill Long 5/8/07

The (Human-Eating) Sharks

The headline in Yahoo News today read: "Shark Attacks Woman off Maui." Even though the attack was not fatal, such an experience can wreck your day and tend to discourage people from swimming around the (Kihei) beach where the attack occurred. The article went on to say that the probable culprit of the attack was a "tiger shark." I decided that I would spend some time today trying to understand one sliver of the phylum Chordata--the Class Chondrichthyes, an 800-species Class comprising sharks, rays, skates. In order to make this more precise, I will focus this essay on the four most dangerous sharks to people, the great white, bull, oceanic whitetip and tiger sharks. I also learned, or re-learned, a lot of vocabulary, and so we will also review some of these words.

Getting Our Bearings in Phylum Chordata

Humans, as well as about 85,000 other species, are members of the Phylum Chordata. A phylum used to be the second most all-inclusive term in the Linnaean classification system which I was taught about 40 years ago, but now the phlyum designation is the sixth most inclusive category. We have the "domain"--Eukaryota; the "kingdom"--Animalia; the "sub-kingdom"-- Eumetazoa; then an "unranked" category of Bilateria and a "superphylum" of Deuterostomia. Phew. The world has become a lot more complex since the "cladistics revolution" of the last 30 or so years, and we see one of its manifestations in the increased groupings of the Linnaean system.

The Phylum Chordata, our home base, has, depending on how you count, about a dozen Classes in it. There are "subphyla" of the Urochordata (Tunicates) or Cephalochordata (Lancelets), "infraphyla" of the Agnatha ("jawless") or Gnathostomata ("jawed") fish, as well as a few "superclasses," too. I suppose it depends on where you are working along the taxonomical scale as to how many of these terms are your "bread and butter." We saw yesterday in my essay on ants, for example, that all the action is in the families, subfamilies, tribes, genera and species. If, however, you want to work on classifications of more inclusive groups, the terminology just listed will be your food and drink. Oh, before I forget, a few of the Classes in Phylum Chordata are Amphibia, Sauropsida (reptiles), Aves, Synapsida (mammal-like "reptiles"), Mammalia, Actinopyterygii ("ray-finned" fish) and Sarcopterygii ("lobe-finned" fish). Our sharks are included in the Chondrichthyes, which means the "cartilaginous fish."

Before getting to the sharks themselves, a word should be said about the prefix chondri. Behind it stands the Greek word chondros, variously translated as "cartilage, gristle, lump, groats, grain." It can be used as the first two syllables in several families/genera of animals, but my interest is in words such as chondralgia, a pain in the cartilage, or chondrarsenite, which is an arsenite of manganese occurring in small grains. We also have chondrigerous, which means "cartilage-bearing" or "making," chondrification, the act or process of making something into cartilage, and chondrenchyme, derived from "cartilage" and enchyma, meaning "infusion," and is a tissue resembling cartilage which occurs in some sponges. There are dozens of other words in the big dictionaries beginning with chondri, but you get the idea by now.

Moving to the Sharks

Well, the sharks fit into this Class because their body is not made out of bones but of cartilage. Within the Chondrichthyes we have eight Orders of sharks, either 30 or 31 families and then about 400 species of them. There is no need to march through the Orders, though you should know that the two largest are the Carcharhiniformes (about 270 species) and the Squaliformes (about 80 species). Let's turn now to each of the four exemplars of human-killing sharks.

1. A Tiger shark injured the Hawaiian visitor today. Known as the "wastebasket of the sea," because of the unusual things that have been found in its digestive tract (from tires to license plates), the tiger shark is from the Class Carcharhiniformes. By the way, Carcharhiniformes means strong (his, hinos), sharp/jagged formed. I don't know if this relates to the teech (I presume this is the case), or the shape of the body. It is the only shark of the genus Galeocerdo, meaning the "hard-haired shark." Members of this Class have what is known as a nictitating membrane, which is a transparent third eyelid that can be used to cover the eye for protection when the shark is about to strike its prey. Sometimes, in other animals, this membrane is activated to protect the eye from sand and other debris, as in the case of the camel which makes long trips in desert storms. This membrane protects the eyes of the polar bear from snow blindness. Woodpeckers activate this membrane a split second before their beak impacts the trunk of the tree so that the eyeballs will stay in their sockets. I think this would be a tremendously useful thing for humans to have, don't you think? Well, just as we don't have a "penis bone," we don't have a nictitating membrane. The only primate which has such a membrane is the (rare) Calabar angwantibo. When the roll is called up yonder, I think I will ask God about this one.

Many other things could be said about this shark, which has been known to attack humans on many occasions, but I will close with an interesting feature of its reproductive life. According to this article, the male inserts one of its "claspers" or its "valva" into the female's genital opening, which allows sperm then to be introduced. Then the male uses its teeth to hold the female still during this mating procedure, which causes considerable discomfort for the female. Is this an example from nature of the "no pain, no gain" approach to life?

Conclusion

The tiger shark is so-called because the young of the species have stripes along the body, stripes which disappear as the shark matures. It is considered to be the most dangerous shark in Hawaiian waters, and in the decade and a half after 1960 more than 4,500 were hunted down in order to control this threat to the major source of Hawaiian revenue--the tourist industry. One of the historical reasons why tiger shark were not hunted was because they were thought to contain an "aumakua" or divine spirit which imparted strength and protection to people. Here is a discussion of the aumakua in Hawaiian culture.

Let's now turn to the other three variety of killer sharks.

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