Anappendage (oroutgrowth) is an external body part or natural prolongation that protrudes from anorganism's body such as an arm or a leg. Protrusions from single-celledbacteria andarchaea are known as cell-surface appendages or surface appendages. In many kinds ofeukaryotic cell the protrusions are known asmembrane protrusions or cell appendages (examples includemicrovilli andcilia).
Inarthropods, an appendage refers to any of thehomologous body parts that may extend from abody segment, includingantennae,mouthparts (includingmandibles,maxillae and maxillipeds),gills,locomotorlegs (pereiopods forwalking, andpleopods forswimming),sexual organs (gonopods), and parts of thetail (uropods). Typically, each body segment carries one pair of appendages. An appendage which is modified to assist in feeding is known as amaxilliped orgnathopod.[citation needed]
Inannelids lateral protrusions from the body are calledparapodia.
Inechinoderms an appendage called apedicellaria 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 astube feet. Tube feet form part of thewater vascular system and are used for locomotion, food and waste transportation, and respiration.
Allcephalopods, amollusc class, have flexible appendages known ascephalopod limbs. They may have further extensions assuckers.
Invertebrates, an appendage can refer to a locomotor part such as atail,fins on afish,limbs (arms,legs,flippers orwings) on atetrapod; exposedsex organ; defensive parts such ashorns andantlers; orsensory organs such asauricles,proboscis (trunk andsnout) andbarbels.[citation needed]
Appendages may becomeuniramous, as ininsects andcentipedes, where each appendage comprises a single series of segments, or it may bebiramous, as in manycrustaceans, where each appendage branches into two sections.Triramous (branching into three) appendages are also possible.[1]
Allarthropod 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 (chieflyDrosophila melanogaster) with modified appendages, such as legs instead of antennae.[2]
A number ofcell-surface appendages are found inprokaryotes –bacteria andarchaea, and includearchaella,flagella,pili,fimbriae, andprosthecae also calledstalks.
A number of cell-surface appendages may be present on different archaea. Two types of appendage are species-specific;cannulae are specific toPyrodictium species, andhami are specific toAltiarchaeum.[3] Other various types of surface structure includepili,archaella (archaeal flagella), structures calledbindisomes that bind sugars, and posttranslationally modified archaellins and pilins.[4][5]
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 ofbiofilms.[4] Atype 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 toS. solfataricus.[4] Appendage fibres described asIho670 fibres are unique toIgnicoccus hospitalis.[4]
Bacterial cell-surface appendages includeflagella,pili, short attachment pili known asfimbriae, and on some speciescurli fibres.Some bacteria also have stalks known asprosthecae. Other appendages arebacterial nanowires.
Cell appendages aremembrane protrusions that extend from thecell membrane, examples aremicrovilli andcilia.
Aleaf is the main appendage of a plant stem.Prosthechea is a genus oforchids named for the prostheca appendage on the back of thecolumn. Hair like structures known astrichomes are found on many types of plants.