Archedictyon

Archedictyon (plural = archedictya) is the name of a hypothetical scheme of wing venation of the common ancestor of all winged insects.

Description

The nature of the archedictyon is an important in the taxonomic classification of the large, primitive Palaeozoic insects known as Palaeodictyoptera. It was used for this purpose as early as 1854. A National Museum of Natural History database for the study of ants, wasps, bees and termites describes the archedictyon as:

...the primitive original vein network [of] the wings of many of the most ancient insect fossils; the complex network of irregular veinlets between the veins in the outer [three-quarters] of both wings, including the anal lobe.

According to a 1999 paper on the evolution of flght in Palaeoptera the cross veins of some Palaeodictyoptera may be an adaptive feature.

Structure

The archedictyon is believed to have contained between six and eight longitudinal veins, but current understanding of the design is based on a combination of fossil data and speculation.

The "Comstock-Needham system" designed by two entomologists describes these veins and their branches:

• Costa (C): the leading edge of the wing
• Subcosta (Sc): the second longitudinal vein (behind the costa), typically unbranched
• Radius (R): the third longitudinal vein, one to five branches reach the wing margin
• Media (M): the fourth longitudinal vein, one to four branches reach the wing margin
• Cubitus (Cu): fifth longitudinal vein, one to three branches reach the wing margin
• Anal veins (A1, A2, A3): the unbranched veins behind the cubitus.

Crossveins are named based on their relative position to the more prominent longitudinal veins:

• C-SC crossveins run between the costa and subcosta
• R crossveins run between adjacent branches of the radius
• R-M crossveins run between the radius and media
• M-CU crossveins run between the media and cubitus.

Living species

In extant insects, the term implies a retention of primitive characteristics but not necessarily a simplicity of form. Modern insects with wings to which the term archedictyon has been applied include the termite Mastotermes darwiniensis from Australia and the praying mantis Orthodera novaezealandiae. from New Zealand.

The term is also used in the discussion of phasmids. Then it refers to a network of non-directional veins in the costal region of the wing or in the elytron.

Bibliography

• "An enigmatic Palaeozoic stem-group: Paoliida: designation of new taxa from the Upper Carboniferous of the Czech Republic" Archived 2011-07-18 at the Wayback Machine (pdf file)

References