11/18/20101Bugs, Lice, and Fleasby Dwight BowmanARTHROPODSThe word “arthropod” means jointed body. The most numerous organisms on earth, so in some respects, the exoskeleton has been more successful than the backbone. Fortunately, only a few are truly parasitic on humans.Primitive arthropods are suggested to have a form that consists of a body composed of a series of segments where each segment had a pair of jointed appendages, one on each side; down the center of the body extended the tube representing the digestive tract. The exoskeleton, that part which gives them that distinctive “crunch” if you ever happen to crush one, covers the outside of the body and is composed of chitin. To grow or to change their internal and external morphology (the process of metamorphosis), arthropods must change the external cuticle that covers their body. This they do through a process of laying down a new cuticle in a process called molting, and then, the old cuticle is shed or ecdysed.The body is composed of hollow spaces with a gut, heart (an open circulatory system), and gills or tracheae for supplying air.ARTHROPODSFour major groups of Arthopods:The Trilobites comprise a group known only from fossils. The Crustacea compose the group that includes the well known shrimp, lobster, crab, and crayfish, along with the less well known copepods.The Cheliceriformes include the horseshoe crabs and the arachnids (the spiders, scorpions, mites, and ticks). The Uniramia include the Myriapods (millipedes), Chilopods (Centipedes), and the Insects (Hexapods). .There are some obvious differences in the morphology of insects and arachnidsof insects and arachnids. Adult insects have 6 legs, adult arachnids have 8 legs. Adult insects have three major body divisions (head, thorax, and abdomen); adult arachnids have two basic body divisions (cephalothorax and abdomen). BUGS - HEMIPTERAThe order Hemiptera (Heteroptera to some authors) form the group of bugsMajority are predacious or feed on plant juicesTrue bugs tend to be relatively large in size and have a narrow neck that connects the rather thin head with large eyes to the thorax which has six well developed legsCharacterized by a hinged proboscisthat is folded under the head and thorax at rest but which is held such that it protrudes from the front of the insect when it is feeding by piercing the veins of a host or when sucking out body fluid from a plant or its preyThe wings of the bugs tend to be covered on the anterior half with a leathery cuticle only apparent in the transparent posterior wing portionDevelopment is via simple metamorphosis which five nymphal instarsthat feed in a fashion similar to their adult counterpartsThe two important groups in medicine are theKissing bugs and the Bed bugs
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