TAILIEUCHUNG - The Insects - Outline of Entomology 3th Edition - Chapter 2

Chapter 2 E XTERNAL ANATOMY Insects are segmented invertebrates that possess the articulated external skeleton (exoskeleton) characteristic of all arthropods. Groups are differentiated by various modifications of the exoskeleton and the appendages – for example, the Hexapoda to which the Insecta belong. | TIC02 5 20 04 4 48 PM Page 21 Chapter 2 EXTERNAL ANATOMY Feet of leaf beetle left and bush fly right . From scanning electron micrographs by . Reid . Stewart. TIC02 5 20 04 4 48 PM Page 22 22 External anatomy Insects are segmented invertebrates that possess the articulated external skeleton exoskeleton characteristic of all arthropods. Groups are differentiated by various modifications of the exoskeleton and the appendages - for example the Hexapoda to which the Insecta belong section is characterized by having six-legged adults. Many anatomical features of the appendages especially of the mouthparts legs wings and abdominal apex are important in recognizing the higher groups within the hexapods including insect orders families and genera. Differences between species frequently are indicated by less obvious anatomical differences. Furthermore the biomechanical analysis of morphology . studying how insects fly or feed depends on a thorough knowledge of structural features. Clearly an understanding of external anatomy is necessary to interpret and appreciate the functions of the various insect designs and to allow identification of insects and their hexapod relatives. In this chapter we describe and discuss the cuticle body segmentation and the structure of the head thorax and abdomen and their appendages. First some basic classification and terminology needs to be explained. Adult insects normally have wings most of the Pterygota the structure of which may diagnose orders but there is a group of primitively wingless insects the apterygotes see section and Box for defining features . Within the Insecta three major patterns of development can be recognized section . Apterygotes and non-insect hexapods develop to adulthood with little change in body form ametaboly except for sexual maturation through development of gonads and genitalia. All other insects either have a gradual change in body form hemime-taboly with external wing buds getting

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