# Body plan

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Set of morphological features common to members of a phylum of animals

Modern groups of animals can be grouped by the arrangement of their body structures, so are said to possess different body plans.

A **body plan**, ***Bauplan*** (pl. [German](/source/German_language): ***Baupläne***), or **ground plan** is a set of [morphological](/source/Morphology_(biology)) [features](/source/Phenotypic_trait) common to many members of a [phylum](/source/Phylum) of [animals](/source/Animal).[1] The [vertebrates](/source/Vertebrate) share one body plan, while [invertebrates](/source/Invertebrate) have many.

This term, usually applied to animals, envisages a "blueprint" encompassing aspects such as [symmetry](/source/Symmetry_(biology)), [layers](/source/Germ_layer), [segmentation](/source/Segmentation_(biology)), [nerve](/source/Nerve), [limb](/source/Limb_(anatomy)), and [gut](/source/Gastrointestinal_tract) disposition. [Evolutionary developmental biology](/source/Evolutionary_developmental_biology) seeks to explain the origins of diverse body plans.

Body plans have historically been considered to have evolved in a flash in the [Ediacaran biota](/source/Ediacaran_biota); filling the [Cambrian explosion](/source/Cambrian_explosion) with the results, and a more nuanced understanding of animal evolution suggests gradual development of body plans throughout the early [Palaeozoic](/source/Palaeozoic). Recent studies in [animals](/source/Animal) and [plants](/source/Plant) started to investigate whether evolutionary constraints on body plan structures can explain the presence of developmental constraints during [embryogenesis](/source/Embryogenesis) such as the phenomenon referred to as [phylotypic stage](/source/Phylotypic_stage).

## History

Among the pioneering [zoologists](/source/Zoologist), Linnaeus identified two body plans outside the vertebrates; Cuvier identified three; and Haeckel had four, as well as the Protista with eight more, for a total of twelve. For comparison, the number of phyla recognised by modern zoologists has risen to 36.[1]

### Linnaeus, 1735

In his 1735 book *[Systema Naturæ](/source/Systema_Naturae)*, Swedish [botanist](/source/Botanist) [Linnaeus](/source/Carl_Linnaeus) grouped the animals into [quadrupeds](/source/Quadrupeds), [birds](/source/Birds), "amphibians" (including [tortoises](/source/Tortoises), [lizards](/source/Lizards) and [snakes](/source/Snakes)), [fish](/source/Fish), "insects" (Insecta, in which he included [arachnids](/source/Arachnids), [crustaceans](/source/Crustaceans) and [centipedes](/source/Centipedes)) and "worms" (Vermes). Linnaeus's Vermes included effectively all other groups of animals, not only [tapeworms](/source/Tapeworms), [earthworms](/source/Earthworms) and [leeches](/source/Leeches) but [molluscs](/source/Molluscs), [sea urchins](/source/Sea_urchins) and [starfish](/source/Starfish), [jellyfish](/source/Jellyfish), [squid](/source/Squid) and [cuttlefish](/source/Cuttlefish).[2]

### Cuvier, 1817

[Haeckel](/source/Haeckel)'s 'Monophyletischer Stammbaum der Organismen' from *Generelle Morphologie der Organismen* (1866) with the three branches [Plantae](/source/Plantae), [Protista](/source/Protista), [Animalia](/source/Animalia)

In his 1817 work, *Le Règne Animal*, French zoologist [Georges Cuvier](/source/Georges_Cuvier) combined evidence from comparative anatomy and [palaeontology](/source/Palaeontology)[3] to divide the animal kingdom into four body plans. Taking the [central nervous system](/source/Central_nervous_system) as the main organ system which controlled all the others, such as the circulatory and digestive systems, Cuvier distinguished four body plans or *embranchements*:[4]

1. with a brain and a spinal cord (surrounded by skeletal elements)[4]
1. with organs linked by nerve fibres[4]
1. with two longitudinal, ventral nerve cords linked by a band with two ganglia below the oesophagus[4]
1. with a diffuse nervous system, not clearly discernible[4]

Grouping animals with these body plans resulted in four branches: [vertebrates](/source/Vertebrates), [molluscs](/source/Molluscs), [articulata](/source/Articulata_hypothesis) (including [insects](/source/Insects) and [annelids](/source/Annelids)) and zoophytes or [Radiata](/source/Radiata).

### Haeckel, 1866

[Ernst Haeckel](/source/Ernst_Haeckel), in his 1866 *Generelle Morphologie der Organismen*, asserted that all living things were [monophyletic](/source/Monophyletic) (had a single evolutionary origin), being divided into plants, protista, and animals. His protista were divided into moneres, protoplasts, flagellates, diatoms, myxomycetes, myxocystodes, rhizopods, and sponges. His animals were divided into groups with distinct body plans: he named these [phyla](/source/Phylum). Haeckel's animal phyla were [coelenterates](/source/Coelenterates), [echinoderms](/source/Echinoderms), and (following Cuvier) articulates, molluscs, and vertebrates.[5]

### Gould, 1979

[Stephen J. Gould](/source/Stephen_J._Gould) explored the idea that the different phyla could be perceived in terms of a Bauplan, illustrating their fixity. However, he later abandoned this idea in favor of [punctuated equilibrium](/source/Punctuated_equilibrium).[6]

## Origin

20 out of the 36 body plans originated in the [Cambrian](/source/Cambrian) period,[7] in the "[Cambrian explosion](/source/Cambrian_explosion)".[8] However, complete body plans of many [phyla](/source/Phylum) emerged much later, in the [Palaeozoic](/source/Palaeozoic) or beyond.[9]

The current range of body plans is far from exhaustive of the possible patterns for life: the [Precambrian](/source/Precambrian) [Ediacaran biota](/source/Ediacara_biota) includes body plans that differ from any found in currently living organisms, even though the overall arrangement of unrelated modern taxa is quite similar.[10] Thus the Cambrian explosion appears to have more or less completely replaced the earlier range of body plans.[7]

## Genetic basis

Further information: [evolutionary developmental biology](/source/Evolutionary_developmental_biology) and [morphogenesis](/source/Morphogenesis)

[Genes](/source/Gene), [embryos](/source/Embryo) and development together determine the form of an adult organism's body, through the complex switching processes involved in [morphogenesis](/source/Morphogenesis).

Developmental biologists seek to understand how genes control the development of structural features through a cascade of processes in which key genes produce [morphogens](/source/Morphogen), chemicals that diffuse through the body to produce a gradient that acts as a position indicator for cells, turning on other genes, some of which in turn produce other morphogens. A key discovery was the existence of groups of [homeobox genes](/source/Homeobox), which function as switches responsible for laying down the basic body plan in animals. The homeobox genes are remarkably conserved between species as diverse as the fruit fly and humans, the basic segmented pattern of the worm or fruit fly being the origin of the segmented spine in humans. The field of animal [evolutionary developmental biology](/source/Evolutionary_developmental_biology), which studies the genetics of [morphology](/source/Morphology_(biology)) in detail, is rapidly expanding[11] with many of the developmental genetic cascades, particularly in the fruit fly *[Drosophila](/source/Drosophila)*, catalogued in considerable detail.[12]

## See also

- [Evolutionary biology portal](https://en.wikipedia.org/wiki/Portal:Evolutionary_biology)
- [Paleontology portal](https://en.wikipedia.org/wiki/Portal:Paleontology)

- [Anatomical terms of location](/source/Anatomical_terms_of_location) – Standard terms for unambiguous description of relative placement of body parts

- [Arthropod head problem](/source/Arthropod_head_problem) – Dispute concerning the evolution of arthropods

- [Deep homology](/source/Deep_homology) – Control of growth and differentiation by deeply conserved genetic mechanisms

- [Evolutionary developmental biology](/source/Evolutionary_developmental_biology) – Comparison of organism developmental processes

- [Definition of Phylum based on body plan](/source/Phylum#Definition_based_on_body_plan) – Taxonomic rank

- [Ediacaran biota](/source/Ediacaran_biota) – Life of the Ediacaran period

- [Macroevolution](/source/Macroevolution) – Evolution on a scale at or above the level of species

- [Precambrian body plans](/source/Precambrian_body_plans) – Structure and development of early multicellular organisms

- [Sean B. Carroll](/source/Sean_B._Carroll) – American evolutionary developmental biologist

- [Segmentation (biology)](/source/Segmentation_(biology)) – Division of some animal and plant body plans into a series of segments

- [Supernumerary body part](/source/Supernumerary_body_part) – Growth of an additional part of the body and a deviation from the body plan

- [Symmetry in biology](/source/Symmetry_in_biology) – Geometric symmetry in living beings

## References

1. ^ [***a***](#cite_ref-Valentine2004_1-0) [***b***](#cite_ref-Valentine2004_1-1) Valentine, James W. (2004). [*On the Origin of Phyla*](https://books.google.com/books?id=DMBkmHm5fe4C). University of Chicago Press. p. 33. [ISBN](/source/ISBN_(identifier)) [978-0226845487](https://en.wikipedia.org/wiki/Special:BookSources/978-0226845487).

1. **[^](#cite_ref-2)** Linnaeus, Carolus (1735). [*Systema naturae, sive regna tria naturae systematice proposita per classes, ordines, genera, & species*](https://www.biodiversitylibrary.org/item/15373). Leiden: Haak. pp. 1–12.

1. **[^](#cite_ref-Reiss2009_3-0)** Reiss, John (2009). [*Not by Design: Retiring Darwin's Watchmaker*](https://books.google.com/books?id=R5bMCUU0tP0C&pg=PA108). University of California Press. p. 108. [ISBN](/source/ISBN_(identifier)) [978-0-520-94440-4](https://en.wikipedia.org/wiki/Special:BookSources/978-0-520-94440-4).

1. ^ [***a***](#cite_ref-DeWit_4-0) [***b***](#cite_ref-DeWit_4-1) [***c***](#cite_ref-DeWit_4-2) [***d***](#cite_ref-DeWit_4-3) [***e***](#cite_ref-DeWit_4-4) De Wit, Hendrik Cornelius Dirk De Wit. *Histoire du Développement de la Biologie*, Volume III, Presses Polytechniques et Universitaires Romandes, Lausanne, 1994, p. 94-96. [ISBN](/source/ISBN_(identifier)) [2-88074-264-1](https://en.wikipedia.org/wiki/Special:BookSources/2-88074-264-1)

1. **[^](#cite_ref-5)** Haeckel, Ernst. *Generelle Morphologie der Organismen : allgemeine Grundzüge der organischen Formen-Wissenschaft, mechanisch begründet durch die von Charles Darwin reformirte Descendenz-Theorie.* (1866) Berlin

1. **[^](#cite_ref-6)** Bowler, Peter J. (2009). *Evolution: the History of an Idea*. California, p. 364.

1. ^ [***a***](#cite_ref-AmSci_7-0) [***b***](#cite_ref-AmSci_7-1) Erwin, Douglas; Valentine, James; Jablonski, David (1997). ["The origin of animal body plans"](https://go.gale.com/ps/i.do?id=GALE%7CA19263512&sid=googleScholar&v=2.1&it=r&linkaccess=abs&issn=00030996&p=AONE&sw=w&userGroupName=nhais_hsck). *American Scientist* (March–April).

1. **[^](#cite_ref-Erwin1999_8-0)** Erwin, D. H. (1999). ["The Origin of Bodyplans"](https://doi.org/10.1093%2Ficb%2F39.3.617). *Integrative and Comparative Biology (American Zoologist)*. **39** (3): 617–629. [doi](/source/Doi_(identifier)):[10.1093/icb/39.3.617](https://doi.org/10.1093%2Ficb%2F39.3.617).

1. **[^](#cite_ref-Budd2000_9-0)** Budd, G. E.; Jensen, S. (2000). "A critical reappraisal of the fossil record of the bilaterian phyla". *Biological Reviews of the Cambridge Philosophical Society*. **75** (2): 253–95. [doi](/source/Doi_(identifier)):[10.1111/j.1469-185X.1999.tb00046.x](https://doi.org/10.1111%2Fj.1469-185X.1999.tb00046.x). [PMID](/source/PMID_(identifier)) [10881389](https://pubmed.ncbi.nlm.nih.gov/10881389). [S2CID](/source/S2CID_(identifier)) [39772232](https://api.semanticscholar.org/CorpusID:39772232).

1. **[^](#cite_ref-10)** Antcliffe, J. B.; Brasier, M. D. (2007). ["Charnia and sea pens are poles apart"](https://oxford.academia.edu/MartinBrasier/Papers/416927/Charnia_and_Sea_Pens_Are_Poles_Apart). *Journal of the Geological Society*. **164** (1): 49–51. [Bibcode](/source/Bibcode_(identifier)):[2007JGSoc.164...49A](https://ui.adsabs.harvard.edu/abs/2007JGSoc.164...49A). [doi](/source/Doi_(identifier)):[10.1144/0016-76492006-080](https://doi.org/10.1144%2F0016-76492006-080). [S2CID](/source/S2CID_(identifier)) [130602154](https://api.semanticscholar.org/CorpusID:130602154).

1. **[^](#cite_ref-11)** Hall, Brian K. (28 March 2005). ["Evo Devo is the New Buzzword..."](http://www.sciam.com/article.cfm?articleID=0005D708-2F7C-123B-AF7C83414B7F0000). *Scientific American*. **292** (4): 102–104. [Bibcode](/source/Bibcode_(identifier)):[2005SciAm.292d.102H](https://ui.adsabs.harvard.edu/abs/2005SciAm.292d.102H). [doi](/source/Doi_(identifier)):[10.1038/scientificamerican0405-102](https://doi.org/10.1038%2Fscientificamerican0405-102). Retrieved 13 September 2014.

1. **[^](#cite_ref-Wallace_12-0)** [Arthur, Wallace.](/source/Wallace_Arthur) (1997). *Animal Body Plans*. Cambridge England: Cambridge University Press. [ISBN](/source/ISBN_(identifier)) [0-521-77928-6](https://en.wikipedia.org/wiki/Special:BookSources/0-521-77928-6).

## External links

- [Developmental Biology 8e Online: Patterning of the Mesoderm by Activin](https://web.archive.org/web/20080508074233/http://8e.devbio.com/article.php?id=117)

**Videos**

- [The Science of Evolution: Sean B. Carroll explains the genetics of the fruit fly body plan.](https://video.on.nytimes.com/?fr_story=3ba8ecaed1cf130c1d0ea4baa3876356bea3bb58)

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Adapted from the Wikipedia article [Body plan](https://en.wikipedia.org/wiki/Body_plan) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Body_plan?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.