Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mecha ...
, class ( la, classis) is a
In biological classification, taxonomic rank is the relative level of a group of organisms (a taxon) in a Taxonomy (biology), taxonomic hierarchy. Examples of taxonomic ranks are species, genus, family (biology), family, order (biology), order, ...
, as well as a taxonomic unit, a
Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechani ...
, in that rank. Other well-known ranks in descending order of size are
Life is a characteristic that distinguishes physical entities
A bubble of exhaled gas in water
In common usage and classical mechanics, a physical object or physical body (or simply an object or body) is a collection of matter within a ...
Domain may refer to:
*Domain of a function
In mathematics, the domain of a Function (mathematics), function is the Set (mathematics), set of inputs accepted by the function. It is sometimes denoted by \operatorname(f), where is th ...
Kingdom may refer to:
* A type of monarchy
* A realm ruled by:
**A king, during the reign of a male monarch
**A queen regnant, during the reign of a female monarch
* Kingdom (biology), a category in biological taxonomy
Arts an ...
In biology, a phylum (; plural
The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, grammatical category of number. The plural of a noun typically denotes a q ...
Order, ORDER or Orders may refer to:
Orderliness is a quality that is characterized by a person’s interest in keeping their surroundings and themselves well organized, and is associated with other qualities such as cleanliness a ...
In human society
A society is a Social group, group of individuals involved in persistent Social relation, social interaction, or a large social group sharing the same spatial or social territory, typically subject to the same Politic ...
Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank
In biological classification
In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circumscribing) and classifying gr ...
In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individu ...
, with class fitting between phylum and order.
The class as a distinct rank of biological classification having its own distinctive name (and not just called a ''top-level genus'' ''(genus summum)'') was first introduced by the
Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the Ancient Greek wo ... Joseph Pitton de Tournefort
Joseph Pitton de Tournefort (5 June 1656 – 28 December 1708) was a French botanist
Botany, also called , plant biology or phytology, is the science
Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic ent ...
in his classification of plants that appeared in his ''Eléments de botanique'', 1694.
Insofar as a general definition of a class is available, it has historically been conceived as embracing taxa that combine a distinct ''grade'' of organization—i.e. a 'level of complexity', measured in terms of how differentiated their organ systems are into distinct regions or sub-organs—with a distinct ''type'' of construction, which is to say a particular layout of organ systems. This said, the composition of each class is ultimately determined by the subjective judgement of
In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circumscribing) and classifying groups of biological organisms based on shared characteristics. Organisms are grouped into taxon, taxa (singular ...
s. Often there is no exact agreement, with different taxonomists taking different positions. There are no objective rules for describing a class, but for well-known animals there is likely to be consensus.
In the first edition of his ''
' (originally in Latin
Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Republic ...
Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement
Ennoblement is the conferring of nobility—the induction of an individual into the noble social class, class. Currently only a few kingdoms still grant nob ...
divided all three of his kingdoms
of Nature (
In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...
Plants are predominantly photosynthetic
Photosynthesis is a process used by plants and other organisms to Energy transformation, convert light energy into chemical energy that, through cellular respiration, can later be released to fuel ...
Animals (also called Metazoa) are multicellular
A multicellular organism is an organism
In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells ...
s) into classes. Only in the animal kingdom are Linnaeus's classes similar to the classes used today; his classes and orders of plants were never intended to represent natural groups, but rather to provide a convenient "artificial key" according to his ''
Linnaean taxonomy can mean either of two related concepts:
# the particular form of biological classification
Biology is the natural science that studies life and living organisms, including their anatomy, physical struc ...
'', largely based on the arrangement of flowers. In botany, classes are now rarely discussed. Since the first publication of the
APG system The APG system (Angiosperm Phylogeny Group system) of plant classification is the first version of a modern, mostly molecular
A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings.
in 1998, which proposed a taxonomy of the
Flowering plants include multiple members of the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek#REDIRECT Greek
Greek may refer to:
Anything of, from, or related to Greece
s up to the level of orders, many sources have preferred to treat ranks higher than orders as informal
A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic – that is, composed of a common ancestor and all its lineage (evolution), lineal descendants - on a phylogenetic tree. R ...
s. Where formal ranks have been assigned, the ranks have been reduced to a very much lower level, e.g. class Equisitopsida for the land plants, with the major divisions within the class assigned to subclasses and superorders.
The class was considered the highest level of the taxonomic hierarchy until
Jean Léopold Nicolas Frédéric, Baron Cuvier (; 23 August 1769 – 13 May 1832), known as Georges Cuvier, was a French naturalist
Natural history is a domain of inquiry involving organisms, including animals, fungus, fungi, and plants, in ...
's ''embranchements'', first called Phyla
Ernst Heinrich Philipp August Haeckel (; 16 February 1834 – 9 August 1919) was a German zoologist
Zoology ()The pronunciation of zoology as is typically regarded as nonstandard, though it is not uncommon. is the branch of biology that stu ...
[Collins, A.G., Valentine, J.W. (2001)]
"Defining phyla: evolutionary pathways to metazoan body plans"
''Evol. Dev''. 3: 432-442.
were introduced in the early nineteenth century.
Hierarchy of ranks below and above the level of class
As with the other principal ranks, classes can be grouped and subdivided. Here are some examples.
Cladistics (; ) is an approach to biological classification
Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular ...
* List of animal classes
Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanism ...
Biology is the natural science
Natural science is a branch of science
Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxonomy (general), o ...
Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer to a specific classification scheme. Originally used only about biological ...
Class or The Class may refer to:
Common uses not otherwise categorized
* Class (biology), a taxonomic rank
* Class (knowledge representation), a collection of individuals or objects
* Class (philosophy), an analytical concept used differently f ...