LABIAL SKELETON AND MUSCULATURE OF THE HYDROCORISAE (HETEROPTERA)

Abstract

The labial skeleton and musculature in representatives of six families of Hydrocorisae are described. The Notonectidae, Naucoridae, Gelastocoridae, Belostomatidae, and Nepidae all possess four-segmented labia with a relatively similar musculature. In Heteroptera the labium is adapted to a fluid diet and thus differs from that of generalized mandibulare insects. The labium of typical Hydrocorisae is compared with that of generalized insects, and the theories of previous authors regarding the possible homologies in the two groups are discussed.In the Corixidae the labial skeleton and musculature are highly modified, differing considerably from those of the other five families of Hydrocorisae. The structure is shortened and broadened, lacking a clear four-part segmentation. Several possible interpretations of its homologies with the labium of typical Hydrocorisae are discussed. Finally, the possible phylogenetic implications of the labial morphology in these six families are considered.