Insecta

The insects, the largest class of the phylum Arthropoda and the largest major grouping of living things, chiefly characterized by flight, great adaptability, vast speciation in terrestrial and freshwater environments, and possession of three pairs of jointed legs and, usually, two pairs of wings. Some are parasitic, others serve as intermediate hosts for parasites, including those that cause many human diseases. Some are wingless; others, such as the Diptera, have only one pair of wings. Respiration is by tracheoles, cuticle-lined air tubes that pass air directly to the tissues. Development in higher forms is holometabolous and passes through distinctive egg, larval, pupal, and adult stages. SYN: Hexapoda. [L. pl. of insectus, insect, fr. in-seco, pp. -sectus, to cut into]

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In·sec·ta in-'sek-tə n pl a class of Arthropoda comprising segmented animals that as adults have a well-defined head bearing a single pair of antennae, three pairs of mouthparts, and usu. a pair of compound eyes, a 3-segmented thorax each segment of which bears a pair of legs ventrally with the second and third often bearing also a pair of wings, and an abdomen usu. of 7 to 10 visible segments without true jointed legs but often with the last segments modified or fitted with specialized extensions (as claspers, stingers, or ovipositors), that breathe air usu. through a ramifying system of tracheae which open externally through spiracles or gills, that exhibit a variety of life cycles often involving complex metamorphosis, and that include the greater part of all living and extinct animals

in·sec·tan -tən adj

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In·sec·ta (in-sekґtə) [L., from in + sectum cut] a class of the Arthropoda whose members are characterized by division of the body into three parts: head, thorax, and abdomen; there are three orders of medical interest, Diptera, Hemiptera, and Siphonaptera.