Arthropods are animals with a hard, outer skeleton and a jointed body and limbs that make up a phylum of invertebrates that includes insects such as ants, butterflies, beetles; crustaceans such as shrimps, lobsters and crabs; arachnids which includes scorpions, spiders and ticks. It was also said that more than one million of their species have been identified.
The name “Arthropoda” comes from the Greek word “arthon” which means joint and “pous which means foot. They are animals which consist of jointed appendages. We can observe that the body of arthropods has a hard outer layer which is the exoskeleton like snails and shrimps. It is made up of calcium carbonate called “chitin” which makes shrimps to be flexible. Though it is not elastic and does resist shrimp to grow they shred the exoskeleton through the process of “molting”. After molting, the arthropod produces a new exoskeleton which is slightly larger than the first and thus allows increase in the size of the arthropod.
Crab vs. Shrimp
If we compare the exoskeleton of a shrimp from a crab we will notice that the crab has a harder exoskeleton. Even both shell are made up of chitin, the crab exoskeleton is much rigid because the chitin of the crab is hardened by lime salts.
Grasshopper vs. Crayfish
Let see the segmentation of the body and appendages of the crayfish and grasshopper. In grasshopper, its body is divided into three main segments which are head, thorax and abdomen. It has two antennas in head that is sensitive when touch and use to smell. Attached to the thorax are three pairs of legs and two wings.
While in crayfish, its body is divided into main segments which are; the fuse, head and the thorax which is called cephalothoraxes and abdomen. Cephalo prefix comes from the Greek term “kephale” which means head. The chitinous exoskeleton covering the cephalothorax of the crayfish is called carapace. The carapace has a pointed extension at the anterior end, it is called rostrum.
The cephalothorax has two long antennae and two short antennules. It is also have five pairs of walking legs; the first pair is enlarged into pinchers. It is also has short appendages called maxillipeds, near the mouth which help in taking in food. The abdomen is modified into a tail fan.
Different Classes of Arthropod
1. Class Insecta or Hexapoda – Insects make up the class Insect which consists of six feet or legs. It has a subphylum Unirama with approximately 29 orders of insects. The prefix hexa- refers to six, and pous means foot.
2. Class Arachnida – The name of the class comes from the Greek word Arachne which means spiders. The class is divided into 11 orders:
- the Acari or Acarina (mites and ticks)
- Amblypygi (tailless whipscorpions)
- Araneae (spiders)
- Opiliones (daddy longlegs)
- Palpigradi (palpigrades)
- Pseudoscorpiones (false scorpions)
- Ricinulei (ricinuleids)
- Schizomida (micro whipscorpions)
- Scorpionida (true scorpions)
- Solpugida (windscorpions)
- Uropygi (whipscorpions)
3. Class Crustacea - The name of the class comes from the Latin term “crusta” which means hard shell or outer cover. The major classes in the subphylum Crustacea are:
- Branchiopoda (fairy shrimps, brine shrimps)
- Ostracoda (mussel, or seed, shrimps)
- Copepoda (copepods)
- Cirripedia (barnacles)
- Malacostraca (crabs, lobsters, shrimps, crayfish, krill, sow bugs, beach hoppers).
4. Class Chilopoda - . The name of the class comes from the Greek “cheilos” which means lip and “pous” for foot.
5. Class Diplopoda - The name of the class comes from the Greek term “diploos” which means double and “pous” for foot; this refer to the fact that the millipede has two pairs of legs in each body segment.
Some insects have adaptation which is called “protective coloration” which they blend on the color of the environment like grasshoppers and katydids which camouflage in green colors.
They have also different structural adaptations which’s allows them to live in wide variety of environment. Just like flea which lives as ectoparasites to animals. Some lives in water like the water strider and giant water bug also called electric-light bug. Because insects are widely distributed in different kinds of environment, it is impossible to wipe them out completely.
The reason why insect are in abundant number is that they reproduce at very fast rate, for example, during times of the year where there is abundant supply of nectar, the queen honeybee lays up to 1000 eggs per day.
Facts about Arthropods
Phylum Arthropoda is the biggest phylum in the animal kingdom. It is composed of almost 750 000 species. Of this number, 700 000 species belong to Class Insecta, 25 000 species belong to Class Crustacea, 15 000 species belong to Class Arachnida, 800 species belong to Class Chilopoda and 200 species belong to Class Diplopoda.
The number of the insect species exceeds those of any arthropod class or any phylum in the animal kingdom. In fact, if we add the number of species of all other animals other than insects, the total will still be less than the number of the insect species. Furthermore, each of the insect species exists in great numbers.
They are also widely distributed on earth. Thus, in terms of number and distribution, insects as a group are very successful inhabitants of this planet. What characteristics of insects explain this success? Insects have many ways of escaping their enemies. Very tiny insects are not easily seen.
Arthropods Life Cycle
One of the interesting facts about insect is the developmental stages. The development of insects from egg to adult is called metamorphosis. The egg of a fly passes through two stages before it become an adult—the larval and pupal stages; this is known as complete metamorphosis. The egg of a grasshopper through only one stage before it becomes an adult—the larval (nymph) stage; this is known as incomplete metamorphosis.
The egg of a silverfish does not pass through any other stage before it becomes an adult. In other words, it has no metamorphosis. The 700 000 species of insects differ in several ways, one in which is the type of development they have.
Effects of Arthropods to Man
Some of the classes of arthropods like crustaceans and insect do really affect us. Lobsters, shrimps and crabs are prized and source of food. Insect also affect us in two important ways.
- Pollination results in fertilization inside flowers and the subsequent development of seeds and fruits.
- We benefits from this directly because many fruits are edible and indirectly because it results in propagation of plants.
We cannot avoid that some insects carry disease organisms. Flies, for example, alight on uncovered food carrying ascaris eggs, bacteria and other microorganism which causes diseases in man.
- Anopheles mosquito can transmit malaria parasite Plasmodium to man.
- Culex mosquito can transmit the filarial worm to man.
- Body louse can transmit Rickettsia which causes typhus fever. T
- Rat flee Xenopsylla can transmit bubonic plague to man.
Some of the insects can also harm us in other ways.
- Grasshopper, locusts, beetles and caterpillars destroy crops and garden plants. Corn borners and grain weevils destroy stored corn and rice.
- Ants and cockroaches cause our food to spoil.
- Moth, silverfish and termites destroy our clothing.
- Termites are notorious for destroying the wooden parts of houses.
- Mosquitoes and bedbugs are common irritants when they bite us.
We usually try to control these insect pests using insecticides and spray’s scantly because they sometimes contain substances which can harm to human.
References ; Wikipedia, the free encyclopedia , Science and Technology by Lilia M. Rabago Ph. D , Crescensia C. Joaquin Ph.D, Catherine B. Lagunzad , PH. D, Encarta
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