Family (biology)

From Wikipedia, the free encyclopedia

The hierarchy of biological classification's eight major taxonomic ranks. An order contains one or more families. Intermediate minor rankings are not shown.

In biological classification, a family (Latin: familia, plural familiae) is a taxonomic rank between order, and genus. A family may be divided into one or more subfamiles, intermediate ranks above the rank of genus. In vernacular usage, a family may also be named after one of its common members, e.g. walnuts and hickory trees belong to the family Juglandaceae, commonly known as the walnut family.

What does and does not belong to each family is determined by a taxonomist — as is whether a particular family should be recognized at all. Often there is no exact agreement, with different taxonomists taking different positions. There are no hard rules that a taxonomist needs to follow in describing or recognizing a family. Some taxa are accepted almost universally, while others are recognised only rarely.

Nomenclature

The naming of families is codified by various international codes.

• In fungal, algal, and botanical nomenclature, the family names of plants, fungi, and algae end with the suffix "-aceae", with the exception of a small number of historic but widely used names including Compositae and Gramineae.^[1]
• In zoological nomenclature, the family names of animals end with the suffix "-idae".^[2]

History

The taxonomic term familia was first used by French botanist Pierre Magnol in his Prodromus historiae generalis plantarum, in quo familiae plantarum per tabulas disponuntur (1689) where he called the seventy-six groups of plants he recognised in his tables families (familiae). The concept of rank at that time was not yet settled, and in the preface to the Prodromus Magnol spoke of uniting his families into larger genera, which is far from how the term is used today.

Carolus Linnaeus used the word familia in his Philosophia botanica (1751) to denote major groups of plants: trees, herbs, ferns, palms, and so on. He used this term only in the morphological section of the book, discussing the vegetative and generative organs of plants. Subsequently, in French botanical publications, from Michel Adanson's Familles naturelles des plantes (1763) and until the end of the 19th century, the word famille was used as a French equivalent of the Latin ordo (or ordo naturalis). In nineteenth-century works such as the Prodromus of Augustin Pyramus de Candolle and the Genera Plantarum of George Bentham and Joseph Dalton Hooker this word ordo was used for what now is given the rank of family.

In zoology, the family as a rank intermediate between order and genus was introduced by Pierre André Latreille in his Précis des caractères génériques des insectes, disposés dans un ordre naturel (1796). He used families (some of them were not named) in some but not in all his orders of "insects" (which then included all arthropods).

Uses

Families can be used for evolutionary, palaeontological and generic studies because they are more stable than lower taxonomic levels such as genera and species.^[3][4]

Order (biology)

From Wikipedia, the free encyclopedia

The hierarchy of biological classification's eight major taxonomic ranks. A class contains one or more orders. Intermediate minor rankings are not shown.

In biological classification, the order (Latin: ordo) is

1. a taxonomic rank used in the classification of organisms and recognized by the nomenclature codes. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family. An immediately higher rank, superorder, may be added directly above order, while suborder would be a lower rank.
2. a taxonomic unit, a taxon, in that rank. In that case the plural is orders (Latin ordines).

Example: Walnuts and hickories belong to the family Juglandaceae (or walnut family), which is placed in the order Fagales.

What does and does not belong to each order is determined by a taxonomist. Similarly for the question if a particular order should be recognized at all. Often there is no exact agreement, with different taxonomists each taking a different position. There are no hard rules that a taxonomist needs to follow in describing or recognizing an order. Some taxa are accepted almost universally, while others are recognised only rarely.

For some groups of organisms, consistent suffixes are used to denote that the rank is an order. The Latin suffix -(i)formes meaning "having the form of" is used for the scientific name of orders of birds and fishes, but not for those of mammals and invertebrates. The suffix -ales is for the name of orders of vascular plants.

Hierarchy of ranks

For some clades covered by the International Code of Zoological Nomenclature, a number of additional classifications are sometimes used, although not all of these are officially recognised.

Name	Meaning of prefix	Example 1	Example 2
Magnorder	magnus: large, great, important	Boreoeutheria
Superorder	super: above	Euarchontoglires	Parareptilia
Grandorder	grand: large	Euarchonta
Mirorder	mirus: wonderful, strange	Primatomorpha
Order		Primates	Procolophonomorpha
Suborder	sub: under	Haplorrhini	Procolophonia
Infraorder	infra: below	Simiiformes	Hallucicrania
Parvorder	parvus: small, unimportant	Catarrhini

In their 1997 classification of mammals, McKenna and Bell used two extra levels between Superorder and Order: "Grandorder" and "Mirorder".^[1] Novacek (1986) inserted them at the same position. Benton (2005) inserted them between superorder and magnorder instead.^[2] This position was adopted by Systema Naturae 2000 and others.

In botany, the ranks of subclass and suborder are secondary ranks pre-defined as respectively above and below the rank of order.^[3] Any number of further ranks can be used as long as they are clearly defined.^[3]

History of the concept 

The order as a distinct rank of biological classification having its own distinctive name (and not just called a higher genus (genus summum)) was first introduced by the German botanist Augustus Quirinus Rivinus in his classification of plants that appeared in a series of treatises in the 1690s. Carolus Linnaeus was the first to apply it consistently to the division of all three kingdoms of nature (minerals, plants, and animals) in his Systema Naturae (1735, 1st. Ed.).

Botany

For plants, Linnaeus' orders in the Systema Naturae and the Species Plantarum were strictly artificial, introduced to subdivide the artificial classes into more comprehensible smaller groups. When the word ordo was first consistently used for natural units of plants, in 19th century works such as the Prodromus of de Candolle and the Genera Plantarum of Bentham & Hooker, it indicated taxa that are now given the rank of family (see ordo naturalis, natural order).

In French botanical publications, from Michel Adanson's Familles naturelles des plantes (1763) and until the end of the 19th century, the word famille (plural: familles) was used as a French equivalent for this Latin ordo. This equivalence was explicitly stated in the Alphonse De Candolle's Lois de la nomenclature botanique (1868), the precursor of the currently used International Code of Nomenclature for algae, fungi, and plants.

In the first international Rules of botanical nomenclature from the International Botanical Congress of 1905, the word family (familia) was assigned to the rank indicated by the French "famille", while order (ordo) was reserved for a higher rank, for what in the 19th century had often been named a cohors^[4] (plural cohortes).

Some of the plant families still retain the names of Linnaean "natural orders" or even the names of pre-Linnaean natural groups recognised by Linnaeus as orders in his natural classification (e.g. Palmae or Labiatae). Such names are known as descriptive family names.

Zoology

In zoology, the Linnaean orders were used more consistently. That is, the orders in the zoology part of the Systema Naturae refer to natural groups. Some of his ordinal names are still in use (e.g. Lepidoptera for the order of moths and butterflies, or Diptera for the order of flies, mosquitoes, midges, and gnats).^{[citation needed]}

Class (biology)

From Wikipedia, the free encyclopedia

The hierarchy of biological classification's eight major taxonomic ranks. Intermediate minor rankings are not shown.

In biological classification, class (Latin: classis) is:

• a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the prefix sub-: subclass (Latin: subclassis).
• a taxonomic unit, a taxon, in that rank. In that case the plural is classes (Latin classes)

The composition of each class is determined by a taxonomist. Often there is no exact agreement, with different taxonomists taking different positions. There are no hard rules that a taxonomist needs to follow in describing a class, but for well-known animals there is likely to be consensus. For example, dogs are usually assigned to the phylum Chordata (animals with notochords); in the class Mammalia; in the order Carnivora.

Hierarchy of ranks

For some clades, a number of alternative classifications are used.

An example from zoology

Name	Meaning of prefix	Example 1	Example 2	Example 3[1]
Superclass	super: above	Tetrapoda
Class		Mammalia	Maxillopoda	Sauropsida
Subclass	sub: under		Thecostraca	Avialae
Infraclass	infra: below		Cirripedia	Aves
Parvclass	parvus: small, unimportant			Neornithes

An example from botanyHistory of the concept

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 French botanist Joseph Pitton de Tournefort in his classification of plants that appeared in his Eléments de botanique, 1694.
In the first edition of his Systema Naturae (1735).^[2] Carolus Linnaeus divided all three of his kingdoms of Nature (minerals, plants, and animals) 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 Systema Sexuale, largely based on the arrangement of flowers.

Since then the class was considered the highest level of the taxonomic hierarchy until George Cuvier's embranchements, first called Phyla by Ernst Haeckel,^[3] were introduced in the early nineteenth century.

Phylum

From Wikipedia, the free encyclopedia

The hierarchy of biological classification's eight major taxonomic ranks. A kingdom contains one or more phyla. Intermediate minor rankings are not shown.

In biology, a phylum (/ˈfaɪləm/; plural: phyla)^{[note 1]} is a taxonomic rank below kingdom and above class. Traditionally, in botany the term division is used instead of "phylum", although in 1993 the International Botanical Congress accepted the designation "phylum".^[1][2] The kingdom Animalia contains approximately 35 phyla; the kingdom Plantae contains 12 phyla. Current research in phylogenetics is uncovering the relationships between phyla, which are contained in larger clades, like Ecdysozoa and Embryophyta.

General description and familiar examples

Concepts of Phyla have changed importantly from their origins in the six Linnaean classes and the four "embranchements" of Georges Cuvier.^[3] Haeckel introduced the term phylum, based on the Greek word phylon.^[4] In plant taxonomy, Eichler (1883) classified all plants into five groups, named divisions.^[5] Informally, phyla can be thought of as grouping organisms based on general specialization of body plan.^[6] At its most basic, a phylum can be defined in two ways: as a group of organisms with a certain degree of morphological or developmental similarity (the phenetic definition), or a group of organisms with a certain degree of evolutionary relatedness (the phylogenetic definition).^[7] Attempting to define a level of the Linnean hierarchy without referring to (evolutionary) relatedness is unsatisfactory, but a phenetic definition is useful when addressing questions of a morphological nature—such as how successful different body plans were.

Definition based on genetic relation

The largest objective measure in the above definitions is the "certain degree"—how unrelated do organisms need to be to be members of different phyla? The minimal requirement is that all organisms in a phylum should be related closely enough for them to be clearly more closely related to one another than to any other group.^[7] Even this is problematic as the requirement depends on knowledge of organisms' relationships: As more data become available, particularly from molecular studies, we are better able to judge the relationships between groups. So phyla can be merged or split if it becomes apparent that they are related to one another or not. For example, the bearded worms were described as a new phylum (the Pogonophora) in the middle of the 20th century, but molecular work almost half a century later found them as a group of annelids and merged the phyla, so that the bearded worms are now an annelid family.^[8] Likewise, the highly parasitic phylum Mesozoa was divided into two phyla Orthonectida and Rhombozoa, when it was discovered the Orthonectida are probably deuterostomes and the Rhombozoa protostomes.^[9]

This changeability of phyla has led some biologists to call for the concept of a phylum to be abandoned in favour of cladistics, a method in which groups are placed on a "family tree" without any formal ranking of group size.^[7]

Definition based on body plan

A definition of a phylum based on body plan has been proposed by paleontologists Graham Budd and Sören Jensen (as Haeckel had done a century earlier). The definition was posited because extinct organisms are typically hardest to classify; they can be off-shoots that diverged from a phylum's line before the characters that define the modern phylum were all acquired. By Budd and Jensen's definition, a phylum is defined by a set of characters shared by all its living representatives.

This approach brings some small problems—for instance, characters common to most members of a phylum may be secondarily lost by some members. It is also defined based on an arbitrary point of time (the present). However, as it is character based, it is easy to apply to the fossil record. A greater problem is that it relies on an subjective decision of which groups of organisms should be considered as phyla.

Its utility is that it makes it easy to classify extinct organisms as "stem groups" to the phyla with which they bear the most resemblance, based only on the taxonomically important similarities.^[7] However, proving that a fossil belongs to the crown group of a phylum is difficult, as it must display a character unique to a sub-set of the crown group.^[7] Furthermore, organisms in the stem group of a phylum can possess the "body plan" of the phylum without all the characteristics necessary to fall within it. This weakens the idea that each of the phyla represents a distinct body plan.^[10]

A classification using this definition is strongly affected by the chance survival of rare groups, which vastly increase the size of phyla. Representatives of many modern phyla did not appear until long after the Cambrian.^[11]

Known phyla

Animal phyla

Phylum	Meaning	Common name	Distinguishing characteristic	Species described
Acanthocephala	Thorny headed worms	Thorny-headed worms	Reversible spiny proboscis that bears many rows of hooked spines	7002756000000000000approx. 756
Acoelomorpha	Without gut	Acoels	No mouth or alimentary canal (alimentary canal = digestive tract in digestive system)
Annelida	Little ring	Segmented worms	Multiple circular segment	700417000000000000017,000+ extant
Arthropoda	Jointed foot	Arthropods	Segmented bodies and jointed limbs, with Chitin exoskeleton	70061134000000000001,134,000+
Brachiopoda	Arm foot	Lamp shells	Lophophore and pedicle	7002300000000000000300-500 extant
Bryozoa	Moss animals	Moss animals, sea mats	Lophophore, no pedicle, ciliated tentacles, anus outside ring of cilia	70035000000000000005,000 extant
Chaetognatha	Longhair jaw	Arrow worms	Chitinous spines either side of head, fins	7002100000000000000approx. 100 extant
Chordata	With a cord	Chordates	Hollow dorsal nerve cord, notochord, pharyngeal slits, endostyle, post-anal tail	7005100000000000000approx. 100,000+
Cnidaria	Stinging nettle	—	Nematocysts (stinging cells)	7004110000000000000approx. 11,000
Ctenophora	Comb bearer	Comb jellies	Eight "comb rows" of fused cilia	7002100000000000000approx. 100 extant
Cycliophora	Wheel carrying	Symbion	Circular mouth surrounded by small cilia, sac-like bodies	70003000000000000003+
Echinodermata	Spiny skin	Echinoderms	Fivefold radial symmetry in living forms, mesodermal calcified spines	7003700000000000000approx. 7,000 extant; approx. 13,000 extinct
Entoprocta	Inside anus	Goblet worm	Anus inside ring of cilia	7002150000000000000approx. 150
Gastrotricha	Hair stomach	—	Two terminal adhesive tubes	7002690000000000000approx. 690
Gnathostomulida	Jaw orifice	Jaw worms		7002100000000000000approx. 100
Hemichordata	Half cord	Acorn worms, pterobranchs	Stomochord in collar, pharyngeal slits	7002100000000000000approx. 100 extant
Kinorhyncha	Motion snout	Mud dragons	Eleven segments, each with a dorsal plate	7002150000000000000approx. 150
Loricifera	Corset bearer	Brush heads	Umbrella-like scales at each end	7002122000000000000approx. 122
Micrognathozoa	Tiny jaw animals	—	Accordion-like extensible thorax	70001000000000000001
Mollusca	Soft	Mollusks / molluscs	Muscular foot and mantle round shell	7005112000000000000112,000[12]
Nematoda	Thread like	Round worms	Round cross section, keratin cuticle	700480000000000000080,000–100,000
Nematomorpha	Thread form	Horsehair worms		7002320000000000000approx. 320
Nemertea	A sea nymph	Ribbon worms		7003120000000000000approx. 1,200
Onychophora	Claw bearer	Velvet worms	Legs tipped by chitinous claws	7002200000000000000approx. 200 extant
Orthonectida	Straight swim		Single layer of ciliated cells surrounding a mass of sex cells	7001200000000000000approx. 20
Phoronida	Zeus's mistress	Horseshoe worms	U-shaped gut	700111000000000000011
Placozoa	Plate animals		Differentiated top and bottom surfaces, two ciliated cell layers, amoeboid fiber cells in between	70001000000000000001
Platyhelminthes	Flat worm	Flatworms		7004250000000000000approx. 25,000[13]
Porifera*	Pore bearer	Sponges	Perforated interior wall	70035000000000000005,000+ extant
Priapulida	Little Priapus			~16
Rhombozoa	Lozenge animal	—	Single anteroposterior axial cell surrounded by ciliated cells	700175000000000000075
Rotifera	Wheel bearer	Rotifers	Anterior crown of cilia	7003200000000000000approx. 2,000
Sipuncula	Small tube	Peanut worms	Mouth surrounded by invertible tentacles	7002144000000000000144–320
Tardigrada	Slow step	Water bears	Four segmented body and head	70031000000000000001,000+
Xenoturbellida	Strange flatworm	—	Ciliated deuterostome	70002000000000000002
Total: 35				2,000,000+

	Protostome	Bilateria
	Deuterostome
	Basal/disputed
	Others (Radiata or Parazoa)

Land plant divisions

The ten Divisions into which plants, here defined as living (extant) land plants, may be placed are shown in the table below. This definition excludes the algal Divisions Chlorophyta and Charophyta which are included in the clade Viridiplantae (see also current definitions of Plantae). The definition and classification of plants at this level varies from source to source. Thus some sources place horsetails in division Arthrophyta and ferns in division Pteridophyta,^[14] while others place them both in Pteridophyta, as shown below. The division Pinophyta may be used for all gymnosperms (i.e. including cycads, ginkgos and gnetophytes),^[15] or for conifers alone as below.

Since the first publication of the APG system in 1998, which proposed a classification of angiosperms to the level of orders, many sources have preferred to treat ranks higher than orders as informal clades. Where formal ranks have been provided, the traditional divisions listed below have been reduced to a very much lower level, e.g. subclasses.^[16]

Division	Meaning	Common name	Distinguishing characteristics
Anthocerotophyta[17]	Anthoceros-like plants	Hornworts	Horn-shaped sporophytes, no vascular system
Bryophyta[18]	Bryum-like plants, moss plants	Mosses	Persistent unbranched sporophytes, no vascular system
Marchantiophyta,[19] Hepatophyta[18]	Marchantia-like plants liver plants	Liverworts	Ephemeral unbranched sporophytes, no vascular system
Lycopodiophyta,[15] Lycophyta[20]	Lycopodium-like plants "wolf" plants	Clubmosses & spikemosses	Microphyll leaves, vascular system
Pteridophyta[citation needed]	Pteris-like plants, fern plants	Ferns & horsetails	Prothallus gametophytes, vascular system
Pinophyta,[citation needed] Coniferophyta[21]	Pinus-like plants Cone-bearing plants	Conifers	Cones containing seeds and wood composed of tracheids
Cycadophyta[22]	Cycas-like plants, palm-like plants	Cycads	Seeds, crown of compound leaves
Ginkgophyta[23]	Ginkgo-like plants	Ginkgo, Maidenhair	Seeds not protected by fruit (single living species)
Gnetophyta[24]	Gnetum-like plants	Gnetophytes	Seeds and woody vascular system with vessels
Flowering plant Anthophyta	flowering plants	Flowering plants, angiosperms	Flowers and fruit, vascular system with vessels
Total: 10

Fungal divisions

Phylum	Meaning	Common name	Distinguishing characteristics
Chytridiomycota	Little pot mushroom	Chytrids	Cellulose in cell walls, flagellated gametes
Deuteromycota	Second mushroom	Imperfect fungi	Unclassified fungi; only asexual reproduction observed no other major distinguishments
Zygomycota	Yoked mushroom	Zygomycetes	Blend gametangia to form a zygosporangium
Glomeromycota	Ball mushroom	None	Form arbuscular mycorrhizae with plants
Ascomycota	Bag/Wineskin Mushroom	Sac fungi	Produce spores in an 'ascus' which is a kind of fruiting bud
Basidiomycota	Pedestal Mushroom	Club Fungi	Produce spores from a 'basidium' which is a kind of fruiting bud
Total: 6

Protista phyla

Bacterial phyla/divisions

Currently there are 29 phyla accepted by List of Prokaryotic names with Standing in Nomenclature (LPSN)^[25]

1. Acidobacteria, phenotipically diverse and mostly uncultured
2. Actinobacteria, High-G+C Gram positive species
3. Aquificae, only 14 thermophilic genera, deep branching
4. Bacteroidetes
5. Caldiserica, formerly candidate division OP5, Caldisericum exile is the sole representative
6. Chlamydiae, only 6 genera
7. Chlorobi, only 7 genera
8. Chloroflexi,
9. Chrysiogenetes, only 3 genera (Chrysiogenes arsenatis, Desulfurispira natronophila, Desulfurispirillum alkaliphilum)
10. Cyanobacteria, also known as the blue-green algae
11. Deferribacteres
12. Deinococcus-Thermus, Deinococcus radiodurans and Thermus aquaticus are "commonly known" species of this phyla
13. Dictyoglomi
14. Elusimicrobia, formerly candidate division Thermite Group 1
15. Fibrobacteres
16. Firmicutes, Low-G+C Gram positive species, such as the spore-formers Bacilli (aerobic) and Clostridia (anaerobic)
17. Fusobacteria
18. Gemmatimonadetes
19. Lentisphaerae, formerly clade VadinBE97
20. Nitrospira
21. Planctomycetes
22. Proteobacteria, the most known phyla, containing species such as Escherichia coli or Pseudomonas aeruginosa
23. Spirochaetes, species include Borrelia burgdorferi, which causes Lyme disease
24. Synergistetes
25. Tenericutes, alternatively class Mollicutes in phylum Firmicutes (notable genus: Mycoplasma)
26. Thermodesulfobacteria
27. Thermomicrobia
28. Thermotogae, deep branching
29. Verrucomicrobia