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Arthropods are the most successful animals on earth as they can live in water, soil, on land and in the air. Included in the group called arthropods are ticks, crabs, shrimp, centipedes, spiders, insects and many others. The arthropods are segmented like earthworms with similiar internal organs.
The skeleton is made of a hard material with flexible joints that is on the outside of the body. Muscles are attached on the inside and the skeletons very much resemble a suit of armor. The arrangement of the skeleton on arthropods makes them have great strength. One example of movement and strength in an arthropod is the lobster. He lives in the water and it is easy to move a heavy body around.
Some of these arthropods are very small insects and are even considered pests but we cannot totally control them as they are so small. They hide easily and do not require much food and reproduce rapidly.
The arthropods have jointed legs and other appendages. Some have mouth parts used for chewing while others have mouth parts used for sucking up juices. They have well-developed nervous systems that enable them to carry out complicated activities.
There are two classes of arthropods. These are the centipedes and the millipedes. These both have segmented bodies and large numbers of legs. On the centipedes there will be one pair of legs on most of the body segments and on the millipedes there will be two pairs. The number of legs will vary. Centipedes and millipedes both are seen in the ground or in a dark, damp area. Centipedes have pincer like poison jaws to catch insects or other small animals. This poison helps to overcome the victims. Some of these are harmless but others can give a painful bite to a person. Millipedes eat decaying plant materials.
Spiders, ticks and scorpions are arachnids and are a part of the arthropod class. They all have eight legs distinguishing them from insects. Ticks are small spider-like types that suck the blood of larger animals and can carry serious diseases in cattle and in man. Spiders have two body parts consisting of a combined head and chest region in front and an abdomen behind. On the chest are the eight legs. It has jaws armed with two poison fangs that are used to kill insects by sucking liquids. The spider will not eat the hard part of the insect. Spiders will creep and jump or even run after their prey. They will spin a web made of silk that comes from glands at the back of the abdomen to trap their prey. Spiders are important in the balance of nature as they keep certain insects in check.
Scorpions look a little like a crayfish but they are not closely related. The scorpion has a long segmented body with a slender abdomen that has a stinger on the end. It has two pairs of mouth parts that are large with pincers on the ends. They take hold of an insect with these pinchers then the abdomen whips over and stings the victim. These arachnids will live in shoes, clothing, under beds or in most any dark place. It is wise It is wise to shake clothing or shoes if you live in an area with an abundance of scorpoions. The scorpion sting can be very painful and is not poisonous except in southern Arizona where there are small, straw-colored scorpions that are very poisonous. If you are bit by a scorpion in this area it is necessary to rush to a hospital for a serum for scorpion stings.
The crustacean class contains crabs, prawns, crayfish, shrimps and lobsters. The crayfish does not have the worm shape of the centipede as the segments and appendages have become specialized to do different jobs. On the front end of the body the segments are grown together so that the head-chest region does not even look segmented. In the rear part of the body the segments are shown clearly. These segments form the abdomen with the intestine running through it.
On the crayfish there are 19 pairs of appendages, 2 pairs of feelers and 6 pairs of mouth parts. There are also 5 pairs of legs, 5 small pairs of appendages under the abdomen, and a pair of tail fins. The mouth parts are used for holding food, cutting it, grinding it, and pushing it in the mouth. Large powerful pincers are on the first pair of legs. The appendages under the abdomen are used in slow, forward swimming, sending water to the gills, and for carrying the eggs until they hatch. Gills are hidden in cavities on each side of the body. Crayfish will hide during the day and hunt at night on tender plants or anything it can find dead or alive.
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