This paper describes the labium in ten representatives of the Corixoidea (Corixidae, Micronectidae and Diaprepocoridae), using scanning electron microscopy. Several new morphological details provide evidence for the external segmentation of the labium of the Corixoidea. The presence of the ventral condyle articulation (cv) is homologous to the condyle of the third segment of the labium in other nepomorphan species, the ventral lobe (vl) is homologous to the second and third segments of the labium, whereas the presence of the latero-ventral plate (lvp) near the apices is homologous to a part of the fourth segment of the labium in the other nepomorphan species. Moreover, the lower apical lobe (apl) and the pair of the sub-oval plates of the apex (ax) are homologous to the apex structures of the labium in other nepomorphans. The slit is a visible boundary between the second and third labial segments on the ventral side only in the Diaprepocoridae. The indication of the homological structural elements of the labium is a new achievement in comparison to earlier descriptions of this organ in several corixoid species. This supports the finding that traces of segmentation have been morphologically preserved in the labium of the Corixoidea, contrary to other previous studies describing the labium as unsegmented. A modified labium of the Corixoidea confirms an assumption about the evolutionary origins of this organ, which posits that it is homologous to the labium of other nepomorphan species.
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Vol. 31 • No. 7