Wing Venation Variation


The following discussions of the subcostal, medial, and radial wing sectors is presented to alleviate any confusion that may surround the use of differning systems of nomenclature applied to crane fly wing venation. Addional sources for descriptions of wing terminology can be found in the Manuals of Nearctic (Wood and Borkent 1989) and Palearctic ( )Diptera.

Subcostal sector
The interpretation of the subcostal veins used here follows that of Alexander and Byers (1989). The subcostal vein (Sc) is located between the costal (C) and radial (R) wing veins, typically angling dorsally and entering the costal vein beyond the wing midlength, but entering the radial vein in Tipulidae and Cylindrotomidae. An additional vein, Sc2 is commonly found connecting Sc and R and is referred to here as Sc2 (Sc-R or sc-r by other authors). The section of Sc distad Sc2 that attains the wing margin is referred to as Sc1 (Sc by other authors). The placement of Sc2 in relation of Sc1 is quite variable, ranging form near allignment with Sc1, to well removed from the free tip of Sc1 and near the wing base. The placement of these two veins serves as an important character that has been used to differentiate between genera and subgenera. The variability in placement of Sc2 along with additional supernumerary crossveins seen in other genera (Geranomyia) does present the possibility that this vein may represent more than one homologous structure.

Radial sector

A commonly used interpretation of the radial and subcostal veins was provided by Alexander (1919; 1927; 1929) and Alexander and Byers (1989). This system is based on the assumption of a sister-group relationship between the Limoniinae and Tipulidae/Cylindrotomidae and their possession of a free element of Sc (Sc2) that corresponds to “the distal section of R1” (Alexander 1929) that is “recognizable by its lack of setae and its angular divergence from R1” (Alexander and Byers 1989). This interpretation originally accepted by Alexander with some reservation, but was then used throughout his proceeding publications. The usage of this system, including the free element of Sc2, is greatly discouraged because of the highly subjective nature by which it is defind, namely that the differentiation of "Sc2" from R1 is largely based on the familiar group of the taxa in question and the inclusion of the said taxa in a family is based partially on the possession of "Sc2".

The system utilized here establishes the ventral most Radial vein as R5 and labels the Radial veins as R1+2, R3, R4, R5 when four veins are present and R1+2+3, R4, R5 when three veins are present. This system is based in the principles of wing veins evolution proposed by Stary (1991). The element referred to as "Sc2" by Alexander and Alexander & Byers is referred to as R1+2 here when the R2 crossvein is present (Fig 2 & 3) and simply R1 when R2 is absent.

Medial sector

Three Medial veins are thought to reach the wing margin in the Dipteran ground plan (Wood & Borkent 1989; Merz & Haenni ). Within the Tipuloidea there are either 2 (M1+2, M3) or 3 (M1, M2, M3) medial veins attaining the wing margin. When three are present they are nearly always joined at the base for distance. The presence of a fourth medial vein corresponding to what is here labeled as CuA2 has been proposed and used by Tipuloidea workers. The use of such as since been canceled, however previous publication may point to its existence.