Spines on the wing veins in Odonara. 3. The vein edge
Advances in odonatology , Volume 6 - Issue 1 p. 21- 43
The wing edge veins have a double row of Sc-type (keel-shaped apse) spines, like those on the convex side of the internal wing veins. On the trading edge the apse of the spines is partially rotated longitudinally: this does not occur in Coenagrionidae and Libelluloidea but does in all other groups (including Anisozygoptera), suggesting that it is a very old character. In Anisoptera, with the exception of Libelluloidea, the apse rotation is complete and the keel separated, resulting in a shape similar to an upside-down heart (“heart-shaped spine”). It is not clear, however, if this represents a convergence between different groups of Anisoptera or if this is a true synapomorphism. The density of the edge spines in Zygoptera (densest at the apex) differs from that in both Anisozygoptera and Anisoptera. The relative density of the two rows of spines also differs between the suborders. Instead, a marked thinning out of the upper row in proximity to the forewing anal field is common in all three suborders. The spines on the lower row tend to be longer than normal, as are those on the inner veins of the cubito-anal field. The different shape and density of the spines on the hind and fore wings modify the air flow existing from the trailing edge, modifications which could be due to different requirements of both wings during flight.
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