The Class Insect1

The Class Insect1 - one pair of antennae on the head •...

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The Class Insecta Insects, Figure 21, are the largest group, with probably over one million identified and named species (and undoubtedly a greater number as yet unknown to us). Insects live in almost all terrestrial and freshwater habitats, with a few species living in the oceans. Many insects have some thoracic appendages modified for flight, as shown in Figure 21, 22. Insects are important as pollinators for flowering plants, as well as for the damage they do annually to crops, and the diseases they transmit (malaria, some forms of encephalitis, Dengue Fever, the West Nile virus, etc.).
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Insects display a wide huge variation in body styles, although there seems to be a size limit on the insect-style of body organization. Common features shared by most living insects include: body composed of three tagmata
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head thorax abodmen one pair of relatively large compound eyes usually three ocelli located on the head
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Unformatted text preview: one pair of antennae on the head • mouthparts consisting of a labrum, a pair of mandibles, a pair of maxillae, a labium, and a tonguelike hypopharynx • two pairs of wings derived from outgrowths of the body wall • three pairs of walking legs Insects have a complete, complex digestive system. They exchange gases through a tracheal system, with external openings called spiracles dividing into finely branched tubules that carry gases directly to metabolizing tissues. Aquatic forms may exchange gases through the body wall or may have various kinds of gills. Excretion of nitrogenous waste takes place via Malpighian tubules. The nervous system of insects is complex, including a number of ganglia and a ventral, double nerve cord. Sense organs are complex and acute. In addition to ocelli and compound eyes, some insects are quite sensitive to sounds, and their chemoreceptive abilities are excellent....
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The Class Insect1 - one pair of antennae on the head •...

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