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BEETLES THAT CANNOT BITE: FUNCTIONAL MORPHOLOGY OF THE HEAD OF ADULT RHYSODINES (COLEOPTERA: CARABIDAE OR RHYSODIDAE)

  • Ross T. Bell (a1)
Abstract
Abstract

In Rhysodini the greatly enlarged mentum forms the entering edge as the beetle wedge-pushes its way through wood. The mandibles cannot bite either wood fibers or food items, but function as a cover for the other mouthparts. The palpi are completely retractile. Each maxilla bears two stylets, the galea and lacinia, and the ligula consists of two bilobed structures. These are apparently the sole feeding structures enabling the beetles to prey on the amoeboid stage of slime molds. The large internal cavity of the head is interpreted as a compromise between a greatly reduced head volume, resulting from reduced jaw musculature, and the need to retain the surface of a full-sized head as part of the wedge-pushing apparatus.

Résumé

Chez les Rhysodini, le mentum très grand forme la bordure antérieure de l’appareil qu’utilise l’animal pour se frayer un chemin dans le bois. Les mandibules sont incapables de mordre les fibres du bois ou les aliments, mais servent à recouvrir les autres pièces buccales. Les palpes sont entièrement rétractiles. Chaque maxille porte deux stylets, la galéa et la lacinie, et la ligule est constituée de deux structures bilobées; il s’agit apparemment des deux seules structures strictement alimentaires qui permettent à ces insectes de capturer les stades améboïdes des moisissures dont ils se nourrissent. La grande cavité qui se trouve à l’intérieur de la tête constitue probablement un compromis : en augmentant la surface de la tête, elle en compense le volume très réduit, résultat de la réduction considérable de la musculature des mâchoires, en assurant au système de creusage de l’animal une surface suffisamment grande pour qu’il soit efficace.

[Traduit par la Rédaction]

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References
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The Canadian Entomologist
  • ISSN: 0008-347X
  • EISSN: 1918-3240
  • URL: /core/journals/canadian-entomologist
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