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The Classification Of Arthropods

By Thomas Keyes
May 23, 2005

One of the most important and interesting phyla of the biological kingdom Animalia is Arthropoda (arthropods). This name derives from the Greek, and literally means "joint legged". Currently Arthropoda are subdivided into ten or more classes, but the more significant classes are these five: Insecta, Arachnida (spiders, scorpions, ticks and mites), Chilopoda (centipedes), Diplopoda (millipedes) and Malacostraca (crabs, shrimp and lobsters).

Usually, the word "insect" conjures up images of annoying, unwholesome little creature, but, of course, Insecta include many beautiful and delightful little beings too, such as butterflies, bees, ladybirds, crickets and fireflies. Insecta are divided into 27 orders: Coleoptera, Collemba, Dermaptera, Dictyoptera, Diptera, Embiidina, Ephemoptera, Grylloblattaria, Hemiptera, Hymenoptera, Lepidoptera, Mantophasmatodea, Mecoptera, Megaloptera, Neuroptera, Odonata, Orthoptera, Phasmida, Phthiraptera, Plecoptera, Psocoptera, Siphonaptera, Strepsiptera, Thysanaptera, Thysanura, Trichoptera and Zoraptera. Unfortunately, orders of insects do not have the sort of distinctive suffix that marks orders of birds, as I mentioned in my article, "The Classification of Birds".

The more interesting orders are Coleoptera (beetles), Dictyoptera (cockroaches, termites and mantises), Diptera (flies, mosquitoes, gnats and midges), Ephemeroptera (Mayflies), Hemiptera (aphids, bedbugs, cicadas, etc.), Hymenoptera (ants, bees, wasps and hornets), Lepidoptera (butterflies amd moths), Orthoptera (crickets, grasshoppers, locusts and katydids), Odonata (dragonflies and damselflies), Phthiraptera (lice, including ordinary human lice, or cooties, crab lice and others), and Siphonaptera (fleas, jiggers). Insect species are so numerous, that common names of insects do not generally refer to particular species, but may refer to whole genera, families or even orders. Thus, there are hundreds of thousands of species of beetles, so that the word "beetle" corresponds to the name of an order, Coleoptera. There are some well-known individual insect species, however: Bombus pennsylvanicus (bumblebee), Cimex lectularius (bedbug), Periplaneta americana (cockroach), Phthiris pubis (crab louse), Musca domestica (housefly), Reticulitermes flavipes (termite), Apis mellifera (honeybee), Anopheles quadrimaculatus (malaria mosquito), Culex pipiens (common mosquito), Orthodera novaezealandiae (praying mantis), Bombyx mori (silkworm, larva of a kind of butterfly), Pulex irritans (human flea), and Pediculus humanus (human louse). Cases where the common name corresponds more closely to a genus rather than a species are: Vespa (hornet), Tabanus (horsefly), Lachnosterna (June bug, a beetle), Glossina (tsetse fly), Vespula and Dolichovespula (both are commonly called yellowjackets, a kind of hornet). This means that usually there are several species sharing a common name, for example, several species of horseflies. Cases where the common name corresponds to the name of a family are: Formicidae (ants), Apidae (bees), Cicadidae (cicadas), Gryllidae (crickets), Lampyridae (fireflies, a kind of beetle), Coccinellidae (ladybirds or ladybugs), Acrididae (locusts) and Vespidae (wasps). Dread insects are malaria mosquitoes, tsetse flies and lice, which can be vectors of bubonic plague and various kinds of dermatitis. Perhaps the most imposing insect is the tarantula hawk wasp, genus Hemipepsis, a huge, formidable black wasp with orange wings that hunts and kills tarantulas. Killer bees are a race of honeybees, known as Apis mellifera scutellata. Other useless insects are: Anthonomus grandis (boll weevil), Diatraea saccharalis (cane borer, larva of a kind of butterfly), and Leucophasma carmodiella (clothes moth).

Incidentally, worms are not included in the class Insecta or the phylum Arthropoda, but rather make up several of their own phyla, such as Platyhelminthes (flatworms), Pogonophora (beard worms), Priapulida (penis worms), Chaetognatha (arrow worms), etc.

Arachnida, the second abovementioned arthropod class, are divided into about 10 orders, of which 5 are interesting: Araneae (spiders); Opiliones (harvestmen or daddylonglegs), Scorpiones (scorpions), Acari (mites and ticks) and Uropygi (vinegaroons). It is to be stressed that arachnids are not insects. I won't dwell on any further comments about arachnid families, genera and species, but will list just a few representative arachnids: Latrodectus mactans (black widow spider), Loxosceles reclusa (brown recluse spider), Mastigoproctus giganteus (vinegaroon or whip scorpion), Achaeranea tepidariorum (house spider), Dermacentor variabilis (dog tick), Lycosa tarantula and Brachypelma smithi (both are kinds of tarantulas).

Malacostraca, which with other groups make up the subphylum Crustacea, include the following representative crustaceans: Homarus americanus (lobster); Palaemon serratus (prawn), Penaeus setiferus (shrimp), Cancer pagurus (edible crab), and Procambarus clarkii (freshwater crayfish). Contemplating crustaceans, one can see, without a microscope, that they must be closely related to insects and arachnids. Compare, for instance, the appearance of a lobster to that of a scorpion.

A very good place to research phylum Arthropoda is the University of Michigan's Animal Diversity Web, which has an exhaustive classification, along with pictures and other information. Its portal to Arthropoda is here: http://animaldiversity.ummz.umich.edu/site/accounts/information/Arthropoda.html

My brief classification and some of the scientific names I have given may not agree 100 % with the Animal Diversity Web's information, as I have used a wide variety of sources. The various classification schemes can never be entirely reconciled, and, moreover, they are constantly changing, as new discoveries are made.

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About the author Thomas Keyes: I have written two books: A SOJOURN IN ASIA (non-fiction) and A TALE OF UNG (fiction), neither published so far.

I have studied languages for years and traveled extensively on five continents.

Email: udikeyes@yahoo.com


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