The preoral cavity of lower Hymenoptera (Insecta): Comparative morphology and phylogenetic significance
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| Authors: | Vilhelmsen, L |
| Year: | 1996 |
| Journal: | Zool. Scr. 25: 143-170 Article Link (DOI) |
| Title: | The preoral cavity of lower Hymenoptera (Insecta): Comparative morphology and phylogenetic significance |
| Abstract: | The skeletal and muscular morphology of the preoral cavity, including the labrum, hypopharynx and labium, was examined in the image in representatives of all the 'symphytan' families as well as the apocritan families Stephanidae, Megalyridae and Trigonalyidae. XyeIidae have complex modifications for masticating pollen, remarkably similiar to those of primitive Lepidoptera. These modifications, collectively termed the triturating basket complex, include an asymmetrical distal epipharyngeal wall with a microtrichial brush and an enlarged infrabuccal pouch with heavy cuticular armature that interacts with the mandibles during feeding. There were striking structural differences between the two subfamilies of Xyelidae in the ligular region; the reduced glossa and clubshaped paraglossae of Macroxyelinae resembles those of primitive Lepidoptera, while the well developed, flattened glossa and paraglossae in Xyelidae are similiar to those of most other 'Symphyta'. A putative transformation series, leading from a relatively large labrum with unsclerotised distal epipharyngeal wall lying anterior to the mandibles, as seen in XyeIidae and Tenthredinoidea, to a small and heavily sclerotised labrum and distal epipharyngeal wall lying posterior to the mandibles, as seen in 'Siricoidea', Orussidae and the Apocrita, was revealed. These modifications may be adaptations to enable the adult of the families pupating in wood to emerge from the pupal chamber. The Anaxyelidae, Orussidae and Apocrita have similiar configurations of the glossa and insertions of the ventral premental adductors. This indicates a close affinity of the Anaxyelidae to Orussidae + Apocrita, a hypothesis that is in conflict with other character systems. The Orussidae and Stephanidae share a unique condition in the development of a pair of large apodemes attached to the labrum; this renders the groundplan state of the labrum in the Apocrita uncertain. Twentyfive characters were defined in an attempt to eludicate the 'Symphyta'-Apocrita transition. A numerical cladistic analysis of the characters was undertaken, resulting in 522 minimum length trees. The characters are also discussed with reference to a cladogram which resulted from an analysis of the characters derived from the present study and a survey of characters from literature. (C) 1996 The Norwegian Academy of Science and Letters |
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