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Labrum (arthropod mouthpart)
Mouthpart of insects and crustaceans / From Wikipedia, the free encyclopedia
The labrum is a flap-like structure that lies immediately in front of the mouth in almost all extant Euarthropoda. The most conspicuous exceptions are the Pycnogonida, which probably are chelicerate-relatives. In entomology, the labrum amounts to the "upper lip" of an insect mouth, the corresponding "lower lip" being the labium.
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The evolutionary origin, embryogenesis and morphological development of the labrum have proved to be by far the most controversial and challenging topic in the study of arthropod head structures.