| ARTHROPODA | ||||
| Introduction
NUMERICAL STRENGTH HABITS AND HABITATS SIGNIFICANCE OF STUDY HISTORY DERIVATION OF NAME DEFINITION GENERAL CHARACTERS CLASSIFICATION
Class 1 TRILOBITA ARACHINDA DISTINCTIVE CHARACTERS OF ARACHINDS MYRIAPODA ONYCHOPHORA
INSECTA GRASS HOPPER OR LOCUST
DISTRIBUTION
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The ‘success’ of a person in the human society is judged by his bank balance and the place he occupies in the society. But when we talk oft the ‘biological success’ of man or any other animal as a species, we consider upon quite different criteria such as: (I) The numbers of species and individuals. (2) Stretches of territory occupied. - (3) Variety of habitats. (4) Amount and kinds of food consumed. (5) capabilities, of defending against enemies, etc. By these standards, Phylum Arthropoda occupies the first place in the Animal Kingdom. It is the largest and the most dominant group of animals on the earth at present. Arthropoda represents a vast assemblage of animals. No one knows how many species of arthropods there are in ‘the world.. it is the largest group in the animal kingdom, outnumbering all the rest by live to one of the total known species of the animals, more than four-fifths i.e.. one million (10,00,000) are arthropods. Of Insecta alone, which constitute only one of the six major classes of arthropods, there are more species (90,00,000) than of all the other 77 or 80 classes of the animal kingdom put together. Many of them are enormously abundant as individuals. However, speaking of biological success in the terms of numbers of species and numbers of individuals, the arthropods have some very close rivals in the Phylum Nematoda. When all the round-worms are finally catalogued, they may eventually outnumber even the arthropods.
They have most successfully established
themselves all over the globe in diverse habitats, wherever life is possible
on earth. They occur over high mountain ranges, 20,000 feet above the sea
level, and have been encountered by airplanes flying miles above the earth.
They have been brought up from the deepest sea bottoms that have been
dredged, some obtained from depths more than five miles in the oceans. They
inhabit fresh-water lakes, streams, ponds, sulphur springs, hot springs and
even pools of petroleum. They live in. the under desert sends, as parasites
in and on the body of other animals and as pests on plants. They have even
invaded the air where they are the most successful of animals. They fly,
hop, crawl and just sit still. Some are gregarious,
Arthropods are economically of great importance to man while men are feverishly contending with each other for materialistic success in terms of fame and fortune; myriads of arthropods are quietly but effectively competing with humans for supremacy in the Animal World. Man has had a very hard time living with the arthropods because of the billions of rupees worth of damage they cause to his economy each year. They consume the largest amount and kinds of food and are most capable of defending themselves against their enemies. There is probably no species of organism that is not on occasion eaten by some arthropod. In turn, the arthropods are eaten by many other animals. They play an important role in the human welfare and health. Strangely enough man can hardly live Without them. Some arthropods are beneficial to man while others are his dreadful enemies. On one hand, many members, such as large crabs, shrimps, prawns, lobsters and locusts, etc., contribute to man’s food supply; others pollinate flowers, destroy pests, supply useful products and provide other valuable services. On the other hand, they destroy crops, food-stores, household goods, clothing, furniture, etc., inflict injury as parasites and transport organisms of dreadful diseases to man, to his livestock and other creatures. . Many fertile regions of the world are still closed to man on account of the presence of the disease-bearing arthropods. The insects, in particular, are the man’s chief competitors for food and shelter. Several times in the history of man, insects, the most successful of all arthropods, have threatened to wipe out man’s food supply and destroy him with disease. Modern man, with his growing knowledge of Zoology and Chemistry, is gradually learning to cope with his arthropod rivals but the strange paradox creates serious problem in arthropod management; for, if we were to destroy all of them, because many were injurious, we would at the same time destroy the beneficial varieties. Consequently, man has got to live with these extremely prolific and efficient creatures and share some of his with them. The arthropods belong to an ancient stock and were well diversified in the past. Today, they are the most dominant animals on the earth, if numbers of different species are accepted as criteria of dominance. Aristotle first described crabs and some other Decapoda and named them Malacostraca or the soft-bodied animals. The great taxonomist Linnaeus put Malacostraca under Insecta which was a very heterogeneous group exactly equivalent to the modern Arthropoda. Linnaeus made the group Insecta opt era to receive the crustaceans, spiders and the myriapods. Jean Baptiste De Monet, Chevalier De Lamarck, the great French philosophical botanist, divided the Linnean Insecta into three crasses— Crustacea, Hexapoda and Arachnida. The name Crustacea was created by Cuvier in 1800, and Lamarck put lobsters, crabs, water-fleas etc., in this class. The name Hexapoda was created for the modern insects but it has not been universally adopted in favour of the present name insecta. Lamarck composed Arachnida for scorpions, spiders, mites, Myriapoda and Thysanura. The name Myriapoda was created by Latreille in l796. The Thysanura are now known to be primitive insects, while Myriapoda is an independent class. Cuvier placed all these animals together with Annelida under the group Articulata. In 1845, C. T. E. Von Siebold separated Annelida from Articulata to make a class of them under the Vermes, while he combined Crustacea, Arachnida and Hexapoda under an independent group, to which he gave the name Arthropoda. The name Arthropoda means ‘jointed legs’, and refers to the most characteristic structure of them. It is, therefore, the jointed nature of the limbs, which has earned the name Arthropoda (Gk., Arthros=jointed; podos= foot) for this phylum. The Arthropoda in general are metamerically segmented coelomate and jointed-limbed animals, with a thick exoskeleton containing chitin, moulting periodically, and without true nephridia and cilia in their structure. It is well presumed that the two phyla had a common origin about 500 million years ago.
Arthropoda is heterogeneous group including a variety of animals. There arc more species of arthropods known to biologists than of all other kinds of living organisms put together. Consequently, there is great disagreement regarding its classification. Some divide it into five classes while others into as many as thirteen classes. However, it seems quite convenient at present to recognize only five classes as shown below: Class I. Crustacea. (L., crusta = a hard shell)—Mostly aquatic. Exoskeleton impregnated with lime salts. Two pairs of antennae and three pairs of jaws. Respiration by gills. Examples: Crabs, Prawns, Lobsters, Barnacles, etc.
Class II. Aracbnoidea. (G., arachne =.spider. oid=like)—Air breathing, terrestrial arthropods. Antennae and true jaws absent. Four pairs of logs. Examples: ‘Spiders. .Scorpions, King-crabs, etc.
Class Ill. Insects. (L., insectum=having been cut into)—Terrestrial. air-breathing arthropods. Body with distinct head, thorax and abdomen. One pair of antennae, three pairs of jaws, three pairs of walking legs and one or two pairs of wings. Respiration by tracheae. Examples : Cockroaches, Houseflies, Silkrnoih, Butterflies, Bees, Mosquitoes, Bugs, Locusts, Ants, Wasps. etc.
Class IV. Myriapoda. (G., myrios = 10 thousand; poda = foot)-Air breathing arthropods with many segmented body One pair of antennae, three pairs of jaws and many pairs of legs. Examples : Millipedes and Centipedes.
Class V. Onychophora. (G., onychos= claw; phoros= bearing) —-Terrestrial, air breathing, primitive, worm-like. Single pair of antennae, eyes and jaws, Numerous stumpy legs. Example: Peripatus. =
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