Odonata

Odonata

Overview
Odonata is an order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

 of insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

s, encompassing dragonflies
Dragonfly
A dragonfly is a winged insect belonging to the order Odonata, the suborder Epiprocta or, in the strict sense, the infraorder Anisoptera . It is characterized by large multifaceted eyes, two pairs of strong transparent wings, and an elongated body...

 (Anisoptera/Epiprocta
Epiprocta
Epiprocta is one of the two extant suborders of the Odonata . It was proposed relatively recently, having been created to accommodate the inclusion of the Anisozygoptera...

) and damselflies
Damselfly
Damselflies are insects in the order Odonata. Damselflies are similar to dragonflies, but the adults can be distinguished by the fact that the wings of most damselflies are held along, and parallel to, the body when at rest...

 (Zygoptera). The word dragonfly is also sometimes used to refer to all Odonata, but the back-formation
Back-formation
In etymology, back-formation is the process of creating a new lexeme, usually by removing actual or supposed affixes. The resulting neologism is called a back-formation, a term coined by James Murray in 1889...

 odonate is a more correct English
English language
English is a West Germanic language that arose in the Anglo-Saxon kingdoms of England and spread into what was to become south-east Scotland under the influence of the Anglian medieval kingdom of Northumbria...

 name for the group as a whole. Odonata enthusiasts avoid ambiguity by using the term true dragonfly, or simply Anisopteran, when referring to just the Anisoptera.

Fabricius
Johan Christian Fabricius
Johan Christian Fabricius was a Danish zoologist, specialising in "Insecta", which at that time included all arthropods: insects, arachnids, crustaceans and others...

 coined the term Odonata from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 οδόντoς (οδούς), odontos (tooth) apparently because they have teeth on their mandibles, even though most insects also have toothed mandibles.

This order has traditionally been grouped together with the mayflies
Mayfly
Mayflies are insects which belong to the Order Ephemeroptera . They have been placed into an ancient group of insects termed the Palaeoptera, which also contains dragonflies and damselflies...

 and several extinct orders in a group called the "Paleoptera
Paleoptera
The name Palaeoptera has been traditionally applied to those primitive groups of winged insects that lacked the ability to fold the wings back over the abdomen as characterizes the Neoptera...

", but this grouping might be paraphyletic.
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Encyclopedia
Odonata is an order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

 of insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

s, encompassing dragonflies
Dragonfly
A dragonfly is a winged insect belonging to the order Odonata, the suborder Epiprocta or, in the strict sense, the infraorder Anisoptera . It is characterized by large multifaceted eyes, two pairs of strong transparent wings, and an elongated body...

 (Anisoptera/Epiprocta
Epiprocta
Epiprocta is one of the two extant suborders of the Odonata . It was proposed relatively recently, having been created to accommodate the inclusion of the Anisozygoptera...

) and damselflies
Damselfly
Damselflies are insects in the order Odonata. Damselflies are similar to dragonflies, but the adults can be distinguished by the fact that the wings of most damselflies are held along, and parallel to, the body when at rest...

 (Zygoptera). The word dragonfly is also sometimes used to refer to all Odonata, but the back-formation
Back-formation
In etymology, back-formation is the process of creating a new lexeme, usually by removing actual or supposed affixes. The resulting neologism is called a back-formation, a term coined by James Murray in 1889...

 odonate is a more correct English
English language
English is a West Germanic language that arose in the Anglo-Saxon kingdoms of England and spread into what was to become south-east Scotland under the influence of the Anglian medieval kingdom of Northumbria...

 name for the group as a whole. Odonata enthusiasts avoid ambiguity by using the term true dragonfly, or simply Anisopteran, when referring to just the Anisoptera.

Etymology


Fabricius
Johan Christian Fabricius
Johan Christian Fabricius was a Danish zoologist, specialising in "Insecta", which at that time included all arthropods: insects, arachnids, crustaceans and others...

 coined the term Odonata from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 οδόντoς (οδούς), odontos (tooth) apparently because they have teeth on their mandibles, even though most insects also have toothed mandibles.

Systematics and taxonomy


This order has traditionally been grouped together with the mayflies
Mayfly
Mayflies are insects which belong to the Order Ephemeroptera . They have been placed into an ancient group of insects termed the Palaeoptera, which also contains dragonflies and damselflies...

 and several extinct orders in a group called the "Paleoptera
Paleoptera
The name Palaeoptera has been traditionally applied to those primitive groups of winged insects that lacked the ability to fold the wings back over the abdomen as characterizes the Neoptera...

", 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
Insect flight
Insects are the only group of invertebrates known to have evolved flight. Insects possess some remarkable flight characteristics and abilities, still far superior to attempts by humans to replicate their capabilities. Even our understanding of the aerodynamics of flexible, flapping wings and how...

 for a detailed discussion).

In some treatments, the Odonata are understood in an expanded sense, essentially synonymous with the superorder Odonatoptera
Odonatoptera
The Odonatoptera are a superorder of ancient winged insects, placed in the Palaeoptera which probably form a paraphyletic group however...

 but not including the prehistoric Protodonata
Protodonata
Meganisoptera is an extinct order of very large to gigantic insects often called griffenflies. The order was formerly named Protodonata for their similar appearance and relation to dragonflies...

. In this approach, instead of Odonatoptera, the term Odonatoidea is used. The systematics
Systematics
Biological systematics is the study of the diversification of terrestrial life, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees...

 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
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...

.

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
Epiprocta
Epiprocta is one of the two extant suborders of the Odonata . It was proposed relatively recently, having been created to accommodate the inclusion of the Anisozygoptera...

 (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
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 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).

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

Size


The largest living odonate is the giant Central America
Central America
Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...

n helicopter damselfly Megaloprepus coerulatus (Zygoptera: Pseudostigmatidae) with a wing span of 191 mm. The heaviest living odonates are Tetracanthagyna
Tetracanthagyna
Tetracanthagyna is a genus of dragonflies in the family Aeshnidae.T. plagiata is the world's largest dragonfly by wingspan and the female T...

  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
Mecistogaster
Mecistogaster is a genus of large Neotropical damselflies in the family Pseudostigmatidae. It contains the following species:*Mecistogaster amalia - Amalia Helicopter*Mecistogaster amazonica *Mecistogaster asticta...

 linearis
(Zygoptera: Pseudostigmatidae) with a body length of 135 mm. Sometimes the Giant Hawaiian Darner
Giant Hawaiian Darner
The Giant Hawaiian Darner, also known as the Giant Hawaiian Dragonfly or Pinao , is a species of dragonfly in the family Aeshnidae. It is one of two species of dragonfly that is endemic to the Hawaiian Islands. It is particularly common at higher elevations.This species is one of the largest of all...

 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
Paleozoic
The Paleozoic era is the earliest of three geologic eras of the Phanerozoic eon, spanning from roughly...

 "giant dragonflies" like Meganeuropsis permiana from the Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...

 of North America with up to 71 cm wing span and 43 cm body length have been the largest insects of all times and belonged to the order Meganisoptera, the griffenflies, 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
Agriocnemis
Agriocnemis is a genus of damselfly in family Coenagrionidae. They are small insects, commonly known as Wisps.It contains the following species:*Agriocnemis aderces *Agriocnemis alcyone *Agriocnemis angolense...

(Zygoptera: Coenagrionidae) with a wing span of only 17-18 mm.

Description




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
Antenna (biology)
Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....

. The mouthparts
Insect mouthparts
Insects exhibit a range of mouthparts, adapted to particular modes of feeding. The earliest insects had chewing mouthparts...

 are on the underside of the head and include simple chewing mandibles
Mandible (arthropod)
thumb|250px|The mandibles of a [[Bull ant]]The mandible of an arthropod is either of a pair of mouthparts used for biting, cutting and holding food. Mandibles are often simply referred to as jaws. Mandibles are present in the extant subphyla Myriapoda , Crustacea and Hexapoda...

 in the adult.

In most families there is a structure on the leading edge near the tip of the wing called the pterostigma
Pterostigma
The pterostigma is a cell in the outer wing of insects which is often thickened or coloured and so stands out from other cells. It is particularly noticeable in dragonflies, but present also in other insect groups, such as snakeflies, hymenopterans and megalopterans.The purpose of the pterostigma,...

. This is a thickened, hemolymph
Hemolymph
Hemolymph, or haemolymph, is a fluid in the circulatory system of some arthropods and is analogous to the fluids and cells making up both blood and interstitial fluid in vertebrates such as birds and mammals...

–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 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 gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...

s on the abdomen, while dragonfly nymphs respire through an organ in their rectum
Rectum
The rectum is the final straight portion of the large intestine in some mammals, and the gut in others, terminating in the anus. The human rectum is about 12 cm long...

.

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 between the eyes.

Ecology and life cycle


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 to those found in other insects. These include grasping cerci
Cercus
Cerci are paired appendages on the rear-most segments of many arthropods, including insects and arachnids but not crustaceans. Cerci often serve as sensory organs, but they may also be used as weapons or copulation aids, or they may simply be vestigial structures.Typical cerci may appear to be...

 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.


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 instar
Instar
An instar is a developmental stage of arthropods, such as insects, between each molt , until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form. Differences between instars can often be seen in altered body proportions, colors, patterns, or...

s with approximately 9–14 molts
Moult
In biology, moulting or molting , also known as sloughing, shedding, or for some species, ecdysis, is the manner in which an animal routinely casts off a part of its body , either at specific times of year, or at specific points in its life cycle.Moulting can involve the epidermis , pelage...

 that are (in most species) voracious predators on other aquatic organisms, including small fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

es. The nymphs
Nymph (biology)
In biology, a nymph is the immature form of some invertebrates, particularly insects, which undergoes gradual metamorphosis before reaching its adult stage. Unlike a typical larva, a nymph's overall form already resembles that of the adult. In addition, while a nymph moults it never enters a...

 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. Male odonates have a copulatory organ on the ventral side of abdominal segment 2 in which they store sperm
Sperm
The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...

atozoa; 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, and resembles a loveheart.

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