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The mesothorax is the middle of the three segments of the
thorax The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the crea ...
of hexapods, and bears the second pair of legs. Its principal
sclerite A sclerite ( Greek , ', meaning " hard") is a hardened body part. In various branches of biology the term is applied to various structures, but not as a rule to vertebrate anatomical features such as bones and teeth. Instead it refers most commonl ...
s (exoskeletal plates) are the mesonotum ( dorsal), the mesosternum (
ventral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
), and the mesopleuron (
lateral Lateral is a geometric term of location which may refer to: Healthcare *Lateral (anatomy), an anatomical direction *Lateral cricoarytenoid muscle *Lateral release (surgery), a surgical procedure on the side of a kneecap Phonetics *Lateral cons ...
) on each side. The mesothorax is the segment that bears the forewings in all winged insects, though sometimes these may be reduced or modified, as in
beetle Beetles are insects that form the order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 describ ...
s (
Coleoptera Beetles are insects that form the order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 describ ...
) or
Dermaptera Earwigs make up the insect order Dermaptera. With about 2,000 species in 12 families, they are one of the smaller insect orders. Earwigs have characteristic cerci, a pair of forcep-like pincers on their abdomen, and membranous wings folded ...
, in which they are sclerotized to form the
elytra An elytron (; ; , ) is a modified, hardened forewing of beetles (Coleoptera), though a few of the true bugs (Hemiptera) such as the family Schizopteridae are extremely similar; in true bugs, the forewings are called hemelytra (sometimes alterna ...
("wing covers"), and the
Strepsiptera The Strepsiptera are an order of insects with eleven extant families that include about 600 described species. They are endoparasites in other insects, such as bees, wasps, leafhoppers, silverfish, and cockroaches. Females of most species ne ...
, in which they are reduced to form
haltere ''Halteres'' (; singular ''halter'' or ''haltere'') (from grc, ἁλτῆρες, weights held in the hands to give an impetus in leaping) are a pair of small club-shaped organs on the body of two orders of flying insects that provide info ...
s that attach to the mesonotum. All adult insects possess legs on the mesothorax. In some groups of insects, the mesonotum is hypertrophied, such as in
Diptera Flies are insects of the order Diptera, the name being derived from the Greek δι- ''di-'' "two", and πτερόν ''pteron'' "wing". Insects of this order use only a single pair of wings to fly, the hindwings having evolved into advanced ...
,
Hymenoptera Hymenoptera is a large order of insects, comprising the sawflies, wasps, bees, and ants. Over 150,000 living species of Hymenoptera have been described, in addition to over 2,000 extinct ones. Many of the species are parasitic. Females typi ...
, and
Lepidoptera Lepidoptera ( ) is an order (biology), order of insects that includes butterfly, butterflies and moths (both are called lepidopterans). About 180,000 species of the Lepidoptera are described, in 126 Family (biology), families and 46 Taxonomic r ...
), in which the anterior portion of the mesonotum (called the mesoscutum, or simply "scutum") forms most of the dorsal surface of the thorax. In these orders, there is also typically a small sclerite attached to the mesonotum that covers the wing base, called the tegula. In one group of insects, the
Hemiptera Hemiptera (; ) is an order of insects, commonly called true bugs, comprising over 80,000 species within groups such as the cicadas, aphids, planthoppers, leafhoppers, assassin bugs, bed bugs, and shield bugs. They range in size from to aroun ...
, the dorsal surface of the thorax is typically formed primarily of the prothorax, but also in part by the enlarged posterior portion of the mesonotum, called the scutellum; in the
Coleoptera Beetles are insects that form the order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 describ ...
, the scutellum may or may not be visible, usually as a small triangular plate between the elytral bases, thus similar in position to the
Hemiptera Hemiptera (; ) is an order of insects, commonly called true bugs, comprising over 80,000 species within groups such as the cicadas, aphids, planthoppers, leafhoppers, assassin bugs, bed bugs, and shield bugs. They range in size from to aroun ...
n scutellum. In
Diptera Flies are insects of the order Diptera, the name being derived from the Greek δι- ''di-'' "two", and πτερόν ''pteron'' "wing". Insects of this order use only a single pair of wings to fly, the hindwings having evolved into advanced ...
and
Hymenoptera Hymenoptera is a large order of insects, comprising the sawflies, wasps, bees, and ants. Over 150,000 living species of Hymenoptera have been described, in addition to over 2,000 extinct ones. Many of the species are parasitic. Females typi ...
the mesothoracic scutellum is also distinct, but much smaller than the mesoscutum.


See also

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Glossary of entomology terms This glossary of entomology describes terms used in the formal study of insect species by entomologists. A–C A synthetic chlorinated hydrocarbon insecticide, toxic to vertebrates. Though i ...
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Insect morphology Insect morphology is the study and description of the physical form of insects. The terminology used to describe insects is similar to that used for other arthropods due to their shared evolutionary history. Three physical features separate insec ...
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Metathorax The metathorax is the posterior of the three segments in the thorax of an insect, and bears the third pair of legs. Its principal sclerites ( exoskeletal plates) are the metanotum (dorsal), the metasternum (ventral), and the metapleuron (lateral) ...
*
Prothorax The prothorax is the foremost of the three segments in the thorax of an insect, and bears the first pair of legs. Its principal sclerites (exoskeletal plates) are the pronotum ( dorsal), the prosternum (ventral), and the propleuron (lateral) on e ...
*
Thorax (arthropod anatomy) The thorax is the midsection ( tagma) of the hexapod body ( insects and entognathans). It holds the head, legs, wings and abdomen. It is also called mesosoma or cephalothorax in other arthropods. It is formed by the prothorax, mesothorax and m ...


References

Insect anatomy {{insect-anatomy-stub