Notum

Notum

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The notum is the dorsal
Dorsum (biology)
In anatomy, the dorsum is the upper side of animals that typically run, fly, or swim in a horizontal position, and the back side of animals that walk upright. In vertebrates the dorsum contains the backbone. The term dorsal refers to anatomical structures that are either situated toward or grow...

 portion of an 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 thoracic
Thorax
The thorax is a division of an animal's body that lies between the head and the abdomen.-In tetrapods:...

 segment. It is typically a single large sclerite
Sclerite
A sclerite is a hardened body part. The term is used in various branches of biology for various structures including hardened portions of sponges, but it is most commonly used for the hardened portions of arthropod exoskeletons....

. It can be further divided into the alinotum which bears the wings and the postnotum which bears the phragma.

In most winged insects, the structure of each successive notum is quite variable; in the Neoptera
Neoptera
Neoptera is a classification group that includes almost all the winged insects, specifically those that can flex their wings over their abdomens...

, the main flight muscles insert on the notum, so the segment that bears the main pair of wings is typically the one with the most highly developed notum. For example, in Diptera
Diptera
Diptera , or true flies, is the order of insects possessing only a single pair of wings on the mesothorax; the metathorax bears a pair of drumstick like structures called the halteres, the remnants of the hind wings. It is a large order, containing an estimated 240,000 species, although under half...

, Hymenoptera
Hymenoptera
Hymenoptera is one of the largest orders of insects, comprising the sawflies, wasps, bees and ants. There are over 130,000 recognized species, with many more remaining to be described. The name refers to the heavy wings of the insects, and is derived from the Ancient Greek ὑμήν : membrane and...

, and Lepidoptera
Lepidoptera
Lepidoptera is a large order of insects that includes moths and butterflies . It is one of the most widespread and widely recognizable insect orders in the world, encompassing moths and the three superfamilies of butterflies, skipper butterflies, and moth-butterflies...

, the mesonotum is the most hypertrophied sclerite, and is commonly called the scutum. However, there are other groups of insects in which, for reasons other than flight, the pronotum is hypertrophied, such as in all beetle
Beetle
Coleoptera is an order of insects commonly called beetles. The word "coleoptera" is from the Greek , koleos, "sheath"; and , pteron, "wing", thus "sheathed wing". Coleoptera contains more species than any other order, constituting almost 25% of all known life-forms...

s (Coleoptera), and most treehopper
Treehopper
Treehoppers and thorn bugs are members of the family Membracidae, a group of insects related to the cicadas and the leafhoppers. There are about 3,200 known species of treehoppers in over 600 genera...

s (family Membracidae, order Hemiptera
Hemiptera
Hemiptera is an order of insects most often known as the true bugs , comprising around 50,000–80,000 species of cicadas, aphids, planthoppers, leafhoppers, shield bugs, and others...

).

The notum on the first thoracic segment is called pronotum, the second mesonotum, and the third metanotum.

See also

  • Thorax
    Thorax
    The thorax is a division of an animal's body that lies between the head and the abdomen.-In tetrapods:...

  • Tergum
    Tergum
    A tergum is the dorsal portion of an arthropod segment other than the head. The anterior edge is called the base and posterior edge is called the apex or margin. A given tergum may be divided into hardened plates or sclerites commonly referred to as tergites...

  • Sternum
  • Pleuron
    Pleuron (insect)
    The pleuron is a lateral sclerite of thoracic segment of an insect between the tergum and the sternum. The terms pro-, meso- and metapleuron are used respectively for the pleura of the first, second and third thoracic segments....