The Odonata - Dragonflies and Damselflies

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The Odonata is the sister group to Ephemeroptera (Mayflies), together they are the only extant members of the Palaeoptera (Thomas et al 2013). Odonata and Ephemeroptera have had separate histories for about 350My. Earliest odonatan fossils are dated from the Namurian at c. 320Mya.
The odonatan Suborders Anisoptera and Zygoptera diverged about 250Mya (Thomas et al 2013, Davis et al 2011). Major internal branchings within the Suborders originated over 150Mya.
There are a number of other Odonatan suborders which are known only from the fossil record, but modern dragonflies and damselflies are conventionally grouped into the three suborders summarized below.

(Select to show families)
A brief description
Anisoptera13 348 2901 Anisoptera (Selys 1853) - the dragonflies - tend to be larger and more robust than other Odonata. In adults the eyes have a curved dorsal inner margin and are at most separated dorsally by half a diameter. Males have cerci and epiproct modified as clasping organs to grasp the female head during copulation. With a very small number of exceptions the forewings and hindwings differ markedly in shape, the hindwings having a broader basal area. Except in Epiophlebia the discoidal cell is triangular or subtriangular (sometimes degenerate in small forms). In mature individuals wings are normally held horizontally or slightly depressed when at rest. Larvae respire through internal tracheal gills developed from folds of the rectal wall. A strong muscular diaphragm pumps water in and out of the rectum to aerate the gills, and this mechanism can also be used for 'jet propulsion' when the animal needs to move quickly. The synapomorphy of the compact larva with internal rectal gills probably represents the evolutionary step that opened a 'new adaptive zone' (G G Simpson 1953), enabling the diversification of the Anisoptera.
For stability we have previously followed a traditional family structure, close to Watson et al (1991). We now follow the large scale revision of the Order recently presented by Dijkstra et al. 2013a.
Anisozygoptera0 0 0 Anisozygoptera (Handlirsch 1908) - a paraphyletic 'suborder', which appears as a grade in the evolution of a restricted, crown group, Anisoptera. Erected by Handlirsch on the assumption Zygoptera and Anisoptera descended from Anisozygoptera, a view that is no longer tenable. A rich but heterogeneous fossil fauna is assigned here. The extant family Epiophlebiidae (genus (Epiophlebia) containing three species - one in Japan, one in the Himalayan foothills (Nepal, India, Bhutan) and one in NE China has been placed here by some authors. Originally classified as Zygoptera on the basis of wing venation (Selys 1889, Munz 1919), the recognition of the compact, anisopteran, larval form (Tillyard 1921) led to placement in the 'Anisozygoptera'. There is no evidence Epiophlebia shares derived characters with any of Handlirsh's 'Anisozygoptera'. Epiophlebia characters are 'intermediate' between Zygoptera and Anisoptera. The wings are similar in shape (hindwings broader) and stemmed at the base. The discoidal cell is quadrilateral (like Zygoptera), but most superficial features resemble crown group Anisoptera. Larvae resemble crown group Anisoptera, but lack the strong diaphragm which enables Anisoptera larvae to 'jet'. Many taxonomists (e.g. Pritykina 1980) now place Epiophlebia as basal Anisoptera rather than as Anisozygoptera. In this interpretation there are no extant 'Anisozygoptera'. We follow this view.
Zygoptera35 284 2754 Zygoptera (Selys 1853) - the damselflies - are generally more slender and delicate in build than other Odonata. In adults the eyes are approximately hemispherical and separated dorsally by at least a diameter. Males have a pair of superior (= cerci) and a pair of inferior (= paraprocts) clasping appendages at the end of the abdomen. The latter are below the anus. The female prothorax is grasped during copulation. Forewings and hindwings are similar in shape; the discoidal cell is quadrilateral, often small. Wings are often held pressed together over the abdomen when at rest. Larvae have hypertrophied paraprocts and epiproct (at the end of the abdomen). In most families these are modified to provide tracheated respiratory structures, whether lanceolate, triquetral or saccoid. This character is almost certainly a symplesiomorphy, but all other lineages are extinct.
For stability we have previously followed a traditional family structure, close to Watson et al (1991). We now follow the large scale revision of the Order recently presented by Dijkstra et al. 2013a and the suborder as further revised in Dijkstra et al. 2013b.
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