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Hemimetabolaa subclass of the class Insecta, including those insects that do not have a marked METAMORPHOSIS, and in which nymphal stages gradually approach the form of the imago at each moult. Examples include EPHEMEROPTERA, ODONATA.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005