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An appendage (or outgrowth) is an external body part or natural prolongation that protrudes from an 's body such as an arm or a leg. Protrusions from single-celled and are known as cell-surface appendages or surface appendages. In many kinds of cells, the protrusions are known as membrane protrusions or cell appendages (examples include and ).


Types in animals
In an appendage called a 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 form part of the water vascular system and are used for locomotion, food and waste transportation, and respiration.

In , an appendage can refer to a locomotor part such as a , on a , limbs (, legs, flippers or ) on a ; exposed ; defensive parts such as horns and ; or such as auricles, proboscis (trunk and ) and barbels.


In protostomes
In worms, lateral protrusions from the body are called . In the class of , lateral protrusions are called .

All , a class, have flexible appendages known as . They may have further extensions as suckers.

In , an appendage refers to any of the homologous body parts that may extend from a , including antennae, mouthparts (including mandibles, maxillae and ), , locomotory ( for , and for swimming), (), and parts of the (). All arthropod appendages are variations of the same basic structure (being homologous with one another), and which structure is produced is controlled by "" genes; alterations to these genes have allowed scientists to produce genetically modified animals, such as fruit flies ( Drosophila melanogaster) with legs growing where the antennae would have on the head.

Appendages may become , as in and , where each appendage comprises a single series of segments, or it may be , as in many , where each appendage branches into two sections. Triramous (branching into three) appendages are also possible. In the past this difference in leg development became the basis of arthropod classification, with being a former group within Arthropoda.


Types in prokaryotes
A number of cell-surface appendages are found in and , and include , , , fimbriae, and prosthecae also called stalks.


Archaea
A number of cell-surface appendages may be present on different archaea. Two types of appendage are species-specific; cannulae are specific to species, and hami are specific to . Other various types of surface structure include , (archaeal flagella), structures called bindisomes that bind sugars, and posttranslationally modified archaellins and pilins.

Archaella are the similar structures to bacterial flagella, serving the same function in motility, particularly swimming, but with a different composition and action. Pili are used for attachment to surfaces, possible communication between cells enabling cell-to-cell contact allowing genetic transfer, and the formation of . 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. Appendage fibres described as Iho670 fibres are unique to Ignicoccus hospitalis.


Bacteria
Bacterial cell-surface appendages include , , short attachment pili known as fimbriae, and on some species . Some bacteria also have stalks known as . Other appendages are bacterial nanowires.


Types in eukaryotic cells
Cell appendages are membrane protrusions that extend from the , examples are and .


Types in plants
A is the main appendage of a plant stem. is a genus of named for the prostheca appendage on the back of the column. Hair like structures known as are found on many types of plants.


See also


See also
  • Appendicular skeleton

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