The notum (plural nota) is the dorsal portion of an

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pa ...

thoracic 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 ...

segment, or the dorsal surface of the body of nudibranch gastropods. The word "notum" is always applied to dorsal structures; in other words structures that are part of the back of an animal, as opposed to being part of the animal's ventral surface, or underside. This word is used in

entomology Entomology () is the scientific study of insects, a branch of zoology. In the past the term "insect" was less specific, and historically the definition of entomology would also include the study of animals in other arthropod groups, such as ara ...

, the study of insects, and in

malacology Malacology is the branch of invertebrate zoology that deals with the study of the Mollusca (mollusks or molluscs), the second-largest phylum of animals in terms of described species after the arthropods. Mollusks include snails and slugs, clams, ...

, the study of mollusks. In malacology the word is used to describe the back of the body of the taxonomic group of marine, shell-less gastropods that are known as nudibranchs.

In insects

, the notum is the dorsal portion of an

segment. The pterothoracic nota (comprising the meso- and metathoracic segments) have two main divisions - the anterior wing-bearing alinotum and the posterior phragma-bearing postnotom.Cranston, P. S, and P. J Gullan. The Insects: An Outline Of Entomology. 5th ed. Chichester: Wiley-Blackwell, 2014. Print. The phragma, or endotergite, is a transverse infolding of the intersegmental sclerite, and its main function is to provide a reinforcing basis of attachment for the dorsal longitudinal muscles. Accordingly, phragmata tend to be best developed in actively flying insect species. In most winged insects, the structure of each successive notum is quite variable; in the

Neoptera Neoptera (Ancient Greek ''néos'' (“new”) + ''pterón'' (“wing”)) is a classification group that includes most orders of the winged insects, specifically those that can flex their wings over their abdomens. This is in contrast with the mo ...

, 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 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 typic ...

, and

Lepidoptera Lepidoptera ( ) is an order of insects that includes butterflies and moths (both are called lepidopterans). About 180,000 species of the Lepidoptera are described, in 126 families and 46 superfamilies, 10 percent of the total described speci ...

, 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 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 describe ...

), and most treehoppers (family Membracidae, order

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 arou ...

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

In nudibranch gastropods

Nudibranch Nudibranchs () are a group of soft-bodied marine gastropod molluscs which shed their shells after their larval stage. They are noted for their often extraordinary colours and striking forms, and they have been given colourful nicknames to match, ...

s are a large group of

sea slug Sea slug is a common name for some marine invertebrates with varying levels of resemblance to terrestrial slugs. Most creatures known as sea slugs are gastropods, i.e. they are sea snails (marine gastropod mollusks) that over evolutionary tim ...

s, shell-less

marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military ...

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

mollusk Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is e ...

s in the clade Nudibranchia. The dorsal surface of the body of nudibranchs is known as the notum.Gosliner, T.M. 1987. ''Nudibranchs of Southern Africa''

References

Insect anatomy Mollusc anatomy {{insect-anatomy-stub

In insects

In nudibranch gastropods

See also

References