Odonata

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Odonata
Temporal range: Triassic–Recent
[1]
Tau emerald Dec10.jpg
Tau Emerald (Hemicordulia tau) dragonfly
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Subclass: Pterygota
Infraclass: Palaeoptera (disputed)
Superorder: Odonatoptera
Order: Odonata
Fabricius, 1793
Suborders

Epiprocta (dragonflies)
Zygoptera (damselflies)
and see text

Odonata is an order of carnivorous insects, encompassing dragonflies (Anisoptera/Epiprocta) and damselflies (Zygoptera). The word dragonfly is also sometimes used to refer to all Odonata, but odonate is a more correct English name for the group as a whole.[2] Odonata enthusiasts avoid ambiguity by using the term true dragonfly,[3] or simply Anisopteran,[4] when referring to just the Anisoptera. The term Warriorfly has also been proposed.[5] Some 5,900 species have been described in this order.[6]

Etymology[edit]

Fabricius coined the term Odonata from the Greek οδόντoς (οδούς), odontos (tooth) apparently because they have teeth on their mandibles, even though most insects also have toothed mandibles.[7]

Systematics and taxonomy[edit]

This order has traditionally been grouped together with the mayflies and several extinct orders in a group called the "Paleoptera", but this grouping might be paraphyletic. What they do share with mayflies is the nature of how the wings are articulated and held in rest (see insect flight for a detailed discussion).

In some treatments,[8] the Odonata are understood in an expanded sense, essentially synonymous with the superorder Odonatoptera but not including the prehistoric Protodonata. In this approach, instead of Odonatoptera, the term Odonatoidea is used. The systematics of the "Palaeoptera" are by no means resolved; what can be said however is that regardless of whether they are called "Odonatoidea" or "Odonatoptera", the Odonata and their extinct relatives do form a clade.[9]

It was long believed that the Anisoptera were a suborder and that there existed a third one, the "Anisozygoptera" (ancient dragonflies). However, they were combined in the suborder Epiprocta (in which Anisoptera is an infraorder) after it was revealed that the "Anisozygoptera" are a paraphyletic group composed of mostly extinct offshoots of dragonfly evolution. The two living species placed in that group are thus placed in the infraorder Epiophlebioptera, whereas the fossil taxa formerly placed therein are now strewn about the Odonatoptera (or Odonata sensu lato).[10]

Tarsophlebiidae is a prehistoric family of Odonatoptera that can be considered either a basal lineage of Odonata or their immediate sister taxon.

The phylogenetic tree of the orders and suborders of odonates according to Bechly (2002):[11]

Odonatoptera

Geroptera (only Eugeropteridae)


Holodonata

Eomeganisoptera (only "Erasipteridae")




Meganisoptera




Campylopterodea (only Campylopteridae)




Protanisoptera




Triadotypomorpha (only Triadotypidae)




Triadophlebiomorpha




Protozygoptera




Archizygoptera




Tarsophlebioptera (only Tarsophlebiidae)


Odonata

Zygoptera




Sieblosiidae


Epiprocta (= Epiproctophora)

Isophlebioptera




Anisozygoptera (= Epiophlebioptera, restricted to Recent Epiophlebiidae)




Heterophlebioptera




Stenophlebioptera




Anisoptera



















Size[edit]

The largest living odonate is the giant Central American helicopter damselfly Megaloprepus coerulatus (Zygoptera: Pseudostigmatidae) with a wing span of 191 mm. The heaviest living odonates are Tetracanthagyna plagiata (Anisoptera: Aeshnidae) with a wing span of 165 mm, and Petalura ingentissima (Anisoptera: Petaluridae) with a body length of 117 mm (some sources 125 mm) and wing span of 160 mm. The longest living odonate is the Neotropical helicopter damselfly Mecistogaster linearis (Zygoptera: Pseudostigmatidae) with a body length of 135 mm. Sometimes the Giant Hawaiian Darner Anax strenuus (Anisoptera: Aeshnidae) is claimed to be the largest living odonate with an alleged wing span of 190 mm, but this seems to be rather a myth as only 152 mm are scientifically documented.

The fossil Paleozoic "giant dragonflies" like Meganeuropsis permiana from the Permian of North America with up to 71 cm wing span[12][13] and 43 cm body length have been the largest insects of all times and belonged to the order Meganisoptera, the griffinflies, related to odonates but not part of the modern order Odonata in the restricted sense.

The smallest living dragonfly is Nannophya pygmaea (Anisoptera: Libellulidae) from east Asia, which a body length of 15 mm and a wing span of 20 mm, and the smallest damselflies (and smallest odonates of all times) are species of the genus Agriocnemis (Zygoptera: Coenagrionidae) with a wing span of only 17–18 mm.

Description[edit]

Male Blue Ringtail (Austrolestes annulosus), a damselfly (Zygoptera: Lestidae)
Dragonfly (top) and damselfly (bottom) wing shape and venation

These insects characteristically have large rounded heads covered mostly by well-developed, compound eyes, legs that facilitate catching prey (other insects) in flight, two pairs of long, transparent wings that move independently, and elongated abdomens. They have three ocelli and short antennae. The mouthparts are on the underside of the head and include simple chewing mandibles in the adult.[14]

In most families there is a structure on the leading edge near the tip of the wing called the pterostigma. This is a thickened, hemolymph–filled and often colorful area bounded by veins. The functions of the pterostigma are not fully known, but it most probably has an aerodynamic effect[15] and may also have a visual function. More mass at the end of the wing may also reduce the energy needed to move the wings up and down. The right combination of wing stiffness and wing mass could reduce the energy consumption of flying. A pterostigma is also found among other insects, such as bees.

The nymphs have stockier, shorter, bodies than the adults. In addition to lacking wings, their eyes are smaller, their antennae longer, and their heads are less mobile than in the adult. Their mouthparts are modified, with the labium being adapted into a unique prehensile organ for grasping prey. Damselfly nymphs breathe through external gills on the abdomen, while dragonfly nymphs respire through an organ in their rectum.[14]

Although generally fairly similar, dragonflies differ from damselflies in several, easily recognizable traits. Dragonflies are strong fliers with fairly robust bodies and at rest hold their wings either out to the side or out and downward (or even somewhat forward). Damselflies tend to be less robust, even rather weak appearing in flight, and when at rest most species hold their wings folded back over the abdomen (see photograph below, left). Dragonfly eyes occupy much of the animal's head, touching (or nearly touching) each other across the face. In damselflies, there is typically a gap in between the eyes.

Ecology and life cycle[edit]

Odonates are aquatic or semi-aquatic as juveniles. Thus, adults are most often seen near bodies of water and are frequently described as aquatic insects. However, many species range far from water. They are carnivorous throughout their life, mostly feeding on smaller insects.

Male Odonata have complex genitalia, different from those found in other insects. These include grasping cerci for holding the female and a secondary set of copulatory organs on the abdomen in which the sperm are held after being produced by the primary genitals. To mate, the male grasps the female by the thorax or head and bends her abdomen so that her own genitalia can be grasped by the copulatory organs holding the sperm.[14] Male odonates have a copulatory organ on the ventral side of abdominal segment 2 in which they store spermatozoa; they mate by holding the female's head (Anisoptera) or thorax (Zygoptera) with claspers located at the tip of the male abdomen; the female bends her abdomen forward to touch the male organ and receive sperm. This is called the "wheel" position.

Damselflies in copulatory "wheel".
Ovipositing flight of two damselfly couples

Eggs are laid in water or on vegetation near water or wet places, and hatch to produce pronymphs which live off the nutrients that were in the egg. They then develop into instars with approximately 9–14 molts that are (in most species) voracious predators on other aquatic organisms, including small fishes. The nymphs grow and molt, usually in dusk or dawn, into the flying teneral immature adults, whose color is not yet developed. These insects later transform into reproductive adults.

See also[edit]

Footnotes[edit]

  1. ^ Hoell, H.V., Doyen, J.T. & Purcell, A.H. (1998). Introduction to Insect Biology and Diversity, 2nd ed. Oxford University Press. p. 320. ISBN 0-19-510033-6. 
  2. ^ Merriam-Webster Dictionary odonate
  3. ^ Field guide to lower aquarium animals. Cranbrook Institute of Science. 1939. 
  4. ^ Orr, A. G. Dragonflies of Peninsular Malaysia and Singapore. ISBN 983-812-103-7. 
  5. ^ Philip S. Corbet & Stephen J. Brook (2008). Dragonflies. London: Collins. ISBN 978-0-00-715169-1. 
  6. ^ Zhang, Z.-Q. (2011). "Phylum Arthropoda von Siebold, 1848 In: Zhang, Z.-Q. (Ed.) Animal biodiversity: An outline of higher-level classification and survey of taxonomic richness". Zootaxa 3148: 99–103. 
  7. ^ Mickel, Clarence E. (1934). "The significance of the dragonfly name "Odonata"". Annals of the Entomological Society of America 27 (3): 411–414. 
  8. ^ E.g. Trueman & Rowe (2008)
  9. ^ Trueman [2008]
  10. ^ Lohmann (1996), Rehn (2003)
  11. ^ Bechly, G. (2002): Phylogenetic Systematics of Odonata. in Schorr, M. & Lindeboom, M., eds, (2003): Dragonfly Research 1.2003. Zerf - Tübingen. ISSN 1438-034x (CD-ROM)
  12. ^ Dragonfly - The largest complete insect wing ever found
  13. ^ Mitchell, F.L. and Lasswell, J. (2005): A dazzle of dragonflies Texas A&M University Press, 224 pages: page 47
  14. ^ a b c Hoell, H.V., Doyen, J.T. & Purcell, A.H. (1998). Introduction to Insect Biology and Diversity, 2nd ed. Oxford University Press. pp. 355–358. ISBN 0-19-510033-6. 
  15. ^ Norberg, R. Åke. "The pterostigma of insect wings an inertial regulator of wing pitch". Journal of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology 81 (1): 9–22. doi:10.1007/BF00693547. 

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