View source for Appendage

{{Short description|External body part or natural prolongation, that protrudes from an organism's body}}
{{About||I/O appendages in OS/360 and successors|Execute Channel Program#Appendages|the EP by Circa Survive|Appendage (EP)}}
{{Wiktionary|appendage}}
[[File:Procerus middle leg.jpg|thumb|A beetle leg]]
An '''appendage''' (or '''outgrowth''') is an external body part, or natural prolongation, that protrudes from an [[organism]]'s body such as an arm or a leg. Protrusions from single-celled [[bacteria]] and [[archaea]] are known as cell-surface appendages or surface appendages. In many kinds of [[eukaryotic]] cell the protrusions are known as [[membrane protrusion]]s or cell appendages, such as [[microvilli]], and [[cilia]].
==Types in animals==
In [[arthropod]]s, an appendage refers to any of the [[homology (biology)|homologous]] body parts that may extend from a [[body segment]], including [[antenna (biology)|antennae]], [[arthropod mouthparts|mouthparts]] (including [[Mandible (arthropod mouthpart)|mandible]]s, [[maxilla (arthropod mouthpart)|maxilla]]e and maxillipeds), [[gill]]s, [[animal locomotion|locomotor]] [[arthropod leg|leg]]s ([[pereiopod]]s for [[walking]], and [[pleopod]]s for [[aquatic locomotion|swimming]]), [[sexual organ]]s ([[gonopod]]s), and parts of the [[tail]] ([[uropod]]s).  Typically, each body segment carries one pair of appendages.  An appendage which is modified to assist in feeding is known as a '''[[wikt:maxilliped|maxilliped]]''' or '''gnathopod'''.{{citation needed|date=August 2022}}
In [[echinoderm]]s an appendage called a [[pedicellaria]] is found. The end of the pedicellaria consists of valves that give a jaw-like appearance and is thought to be used to clear the external body surface. Echinoderms also possess podia known as [[tube feet]]. Tube feet form part of the [[water vascular system]] and are used for locomotion, food and waste transportation, and respiration.
All [[cephalopod]]s, a [[mollusc]] phylum, have flexible appendages known as [[cephalopod limb]]s. They may have further extensions as [[Sucker (zoology)|suckers]].
In [[vertebrate]]s, an appendage can refer to a locomotor part such as a [[tail]], [[fish fin|fin]]s on a [[fish]], [[limb (anatomy)|limb]]s ([[arm]]s, [[leg#Tetrapod legs|leg]]s, [[flipper (anatomy)|flipper]]s or [[wing]]s) on a [[tetrapod]]; exposed [[sex organ]]; defensive parts such as [[horn (anatomy)|horn]]s and [[antler]]s; or [[sensory organ]]s such as [[auricle (anatomy)|auricle]]s, [[proboscis#Vertebrates|proboscis]] ([[Elephant#Trunk|trunk]] and [[snout]]) and [[barbel (anatomy)|barbel]]s.{{citation needed|date=August 2022}}
Appendages may become ''uniramous'', as in [[insect]]s and [[centipede]]s, where each appendage comprises a single series of segments, or it may be ''biramous'', as in many [[crustacean]]s, where each appendage branches into two sections. ''Triramous'' (branching into three) appendages are also possible.<ref>{{cite journal |last1=Morris |first1=Simon Conway |title=The Burgess Shale (Middle Cambrian) Fauna |journal=Annual Review of Ecology and Systematics |date=1979 |volume=10 |pages=327–349 |doi=10.1146/annurev.es.10.110179.001551 |jstor=2096795 |url=https://www.jstor.org/stable/2096795 |access-date=17 November 2020}}</ref>
All [[arthropod]] appendages are variations of the same basic structure (''homologous''), and which structure is produced is controlled by "[[homeobox]]" genes. Changes to these genes have allowed scientists to produce animals (chiefly ''[[Drosophila melanogaster]]'') with modified appendages, such as legs instead of antennae.<ref>{{cite journal |last1=Emerald |first1=B. Starling |last2=Cohen |first2=Stephen |title=Spatial and temporal regulation of the homeotic selector gene Antennapedia is required for the establishment of leg identity in Drosophila |journal=Developmental Biology |date=March 2004 |volume=267 |issue=2 |pages=462–472 |doi=10.1016/j.ydbio.2003.12.006 |pmid=15013806 |doi-access= }}</ref>
==Types in prokaryotes==
A number of '''cell-surface appendages''' are found in [[prokaryote]]s – [[bacteria]] and [[archaea]], and include [[archaella]], [[flagella]], [[pilus|pili]], [[Pilus#Fimbriae|fimbriae]], and [[Prosthecate bacteria|prosthecae]] also called ''stalks''.
===Archaea===
A number of cell-surface appendages may be present on different archaea. Two types of appendage are species-specific; [[Cannula (archaea)|cannulae]] are specific to ''[[Pyrodictium]]'' species, and [[Hamus (archaea)|hami]] are specific to ''[[Altiarchaeum]]''.<ref name="van Wolferen">{{cite journal |last1=van Wolferen |first1=M |last2=Pulschen |first2=AA |last3=Baum |first3=B |last4=Gribaldo |first4=S |last5=Albers |first5=SV |title=The cell biology of archaea. |journal=Nature Microbiology |date=November 2022 |volume=7 |issue=11 |pages=1744–1755 |doi=10.1038/s41564-022-01215-8 |pmid=36253512|pmc=7613921 }}</ref> Other various types of surface structure include [[pilus|pili]], [[archaella]] (archaeal flagella), structures called ''bindisomes'' that bind sugars, and posttranslationally modified archaellins and pilins.<ref name="Jarrell">{{cite journal |last1=Jarrell |first1=KF |last2=Ding |first2=Y |last3=Nair |first3=DB |last4=Siu |first4=S |title=Surface appendages of archaea: structure, function, genetics and assembly. |journal=Life |date=24 January 2013 |volume=3 |issue=1 |pages=86–117 |doi=10.3390/life3010086 |pmid=25371333 |pmc=4187195 |bibcode=2013Life....3...86J |doi-access=free }}</ref><ref name="Lassak">{{cite journal |last1=Lassak |first1=K |last2=Ghosh |first2=A |last3=Albers |first3=SV |title=Diversity, assembly and regulation of archaeal type IV pili-like and non-type-IV pili-like surface structures. |journal=Research in Microbiology |date=November 2012 |volume=163 |issue=9–10 |pages=630–44 |doi=10.1016/j.resmic.2012.10.024 |pmid=23146836|s2cid=37802794 |doi-access=free }}</ref>
Archaella are the similar structures to bacterial flagella with the same function in motility particularly swimming, but with a different composition and action. Pili are used in attachment to surfaces, possible communication between cells enabling cell to cell contact allowing genetic transfer, and the formation of [[biofilm]]s.<ref name="Jarrell"/> A [[type IV pili]] model is used in the assembly of several cell surface structures. The bindisome is made up of sugar binding proteins to facilitate sugar uptake. So far studies are limited to ''S. solfataricus''.<ref name="Jarrell"/> Appendage fibres described as ''Iho670 fibres'' are unique to ''[[Ignicoccus hospitalis]]''.<ref name="Jarrell"/>
===Bacteria===
Bacterial cell-surface appendages include [[flagella]], [[Pilus|pili]], short attachment pili known as [[Fimbria (bacteriology)|fimbriae]], and on some species [[Curli|curli fibres]].
Some bacteria also have stalks known as [[prosthecae]]. Other appendages are  [[bacterial nanowires]].
==Types in eukaryotes==
Cell appendages are [[membrane protrusion]]s that extend from the [[cell membrane]], examples are [[microvilli]] and [[cilia]].
==Types in plants==
A [[leaf]] is the main appendage of a plant stem.
''[[Prosthechea]]'' is a genus of [[orchid]]s named for the prostheca appendage on the back of the [[Column (botany)|column]]. Hair like structures known as [[trichome]]s are found on many types of plants.
==See also==
* [[Skin appendages]]
* [[Sculpture (mollusc)]]
==References==
{{reflist}}
==See also==
* [[Appendicular skeleton]]
[[Category:Animal anatomy]]