Tuesday, 26 February 2013

PhD week 51: Corbels

A selection of corbels. For larger pictures and my interpretation of the structures, see the examples on my Flickr page.

The corbel is a character on the hind leg that is frequently used in the higher classification of broad-nosed weevils. It is a feature that is difficult to describe in words, and can be tricky to see at first. Unfortunately, there are few easily accessable pictures that show the different types of corbel. This post is an attempt to rectify the situation.

The corbel refers to the form of the apex of the hind tibia. An "Open" corbel has no particular modification to the apex. An "Enclosed" or "Closed" corbel has a flat area (often with scales or short setae) lying between two rows of setae on the outer edge of the tibial apex. When the corbel is large, such as in Leptopius and Cecyropa, it is easily seen. However, sometimes the corbel can be very slender, as shown by Naupactus leucoloma. In such casees, it can be difficult to determine whether the corbel is open or enclosed. A "Semi-enclosed" corbel has a concave area between the apex of the tibia and the insertion of the tarsus that is always bare. It is important to note that the semi-enclosed corbel is not homologous with the enclosed corbel.

An excellent discussion on the corbel, that goes into a lot more depth than I've covered here, can be found on the International Weevil Community Website.

Thompson RT. 1992. Observations on the morphology and classification of weevils (Coleoptera, Curculionidae) with a key to major groups. Journal of Natural History 26: 835–891.

   Ferngren GB (Editor). 2002. Science and Religion. A Historical Introduction Baltimore: The John Hopkins University Press
   Hughes P (Translator). 1937. Meditations for Lent from St. Thomas Aquinas. London: Sheed and Ward
    St Augustine, Betteson H (Translator). 2003. City of God. London: Penguin Classics
   Proverbs 13–16

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