{{Short description|Fibre secreted by some molluscs}} {{Use dmy dates|date=April 2016}} [[File:Mytilus with byssus.jpg|thumb|A mussel (genus ''Mytilus''), attached to a rock by its byssus]] [[Image:Zebra mussel GLERL 1.jpg|thumb|Illustration of the byssus of ''Dreissena polymorpha'', the freshwater zebra mussel]] A '''byssus''' ({{IPAc-en|'|b|I|s|@|s}}) is a bundle of filaments secreted by many species of bivalve mollusc that function to attach the mollusc to a solid surface. Species from several families of clams have a byssus, including pen shells (Pinnidae), true mussels (Mytilidae), and Dreissenidae.
==Filaments== Byssus filaments are created by certain kinds of marine and freshwater bivalve mollusks, which use the byssus to attach themselves to rocks, substrates, or seabeds. In edible mussels, the inedible byssus is commonly known as the "beard", and is removed before cooking.
Many species of mussels secrete byssus threads to anchor themselves to surfaces, with families including the Mytilidae, Arcidae, Anomiidae, Pinnidae, Pectinidae, Dreissenidae, and Unionidae.<ref name="Turner">{{cite journal |last1=Turner |first1=Ruth |last2=Rosewater |first2=Joseph |title=The Family Pinnidae in the Western Atlantic |journal=Johnsonia |date=June 1958 |volume=3 |issue=38 |pages=285–326}}</ref><ref name="Starr">{{cite book |last1=Starr |first1=Cecie |last2=Taggart |first2=Ralph |title=Biology: The Unity and Diversity of Life |date=2004 |publisher=Thomson Learning |location=Belmont, CA}}</ref>
==Mechanics== The byssus, or byssal complex, is composed of multiple extracellular collagenous threads that are placed radially by the mussel from a central stem. Each thread is composed of three regions: a corrugated proximal region close to the mussel body, a longer, smooth distal region connecting the proximal region to the ending plaque, and the adhesive plaque itself, which anchors the mussel to the surface.<ref name="Carrington">{{cite journal |last1=Moeser |first1=Gretchen M. |last2=Carrington |first2=Emily |title=Seasonal variation in mussel byssal thread mechanics |journal=Journal of Experimental Biology |date=15 May 2006 |volume=209 |issue=10 |pages=1996–2003 |doi=10.1242/jeb.02234 |pmid=16651564 |doi-access=free |bibcode=2006JExpB.209.1996M }}</ref> The proximal region consists of a corrugated sheath enveloping loosely-arranged coiled fibers; these coils can unravel to extend the fiber under an applied force. The distal region is more ordered, consisting of aligned collagenous fiber bundles that give the fiber stiffness. The plaque consists of collagen-like fibers over a spongy matrix in which the adhesive protein is deposited and hardens.<ref name="Bell and Gosline" />
The purpose of the byssus is to keep the mussel attached to the desired surface, and to this end byssal threads must be able to withstand strong cyclic motion due to tidal action near the shorelines mussels inhabit. Mechanical testing of live mussels has shown that byssal threads can extend 39% before yield and 64% before breaking, at a nominal strain rate of 10 mm/min.<ref name="Carrington" /> Tensile testing shows that threads exhibit three distinct phases: initial stiffness from both the distal and proximal regions, softening due to yield in the distal region, and finally stiffening directly preceding tensile failure.<ref name="Bell and Gosline">{{cite journal |last1=Bell |first1=Emily |last2=Gosline |first2=John |title=Mechanical design of mussel byssus: material yield enhances attachment strength |journal=Journal of Experimental Biology |date=1 April 1996 |volume=199 |issue=4 |pages=1005–1017 |doi=10.1242/jeb.199.4.1005 |pmid=9318809 |bibcode=1996JExpB.199.1005B |url=https://journals.biologists.com/jeb/article/199/4/1005/7560/Mechanical-design-of-mussel-byssus-material-yield |access-date=9 May 2021|url-access=subscription }}</ref> The ability of the distal region to yield before breaking gives the mussels their characteristic hardiness even under strong tidal forces.<ref name="Bell and Gosline" /> Many variables that influence the performance of byssal threads have been studied, including species variations,<ref name="Brazee">{{cite journal |last1=Brazee |first1=Shanna |last2=Carrington |first2=Emily |title=Interspecific Comparison of the Mechanical Properties of Mussel Byssus |journal=The Biological Bulletin |date=December 2006 |volume=211 |issue=3 |pages=263–274 |doi=10.2307/4134548 |jstor=4134548 |pmid=17179385 |s2cid=24797335 |url=https://www.journals.uchicago.edu/doi/full/10.2307/4134548 |access-date=9 May 2021|url-access=subscription }}</ref> seasonal variations,<ref name="Carrington" /> temperature effects,<ref name="Aldred">{{cite journal |last1=Aldred |first1=Nick |title=Tensile and dynamic mechanical analysis of the distal portion of mussel (Mytilus edulis) byssal threads |journal= Journal of the Royal Society Interface|date=22 December 2007 |volume=4 |issue=17 |pages=1159–1167 |doi=10.1098/rsif.2007.1026 |pmid=17439859 |url= |pmc=2396211 }}</ref> and aging effects.<ref name="Aldred" /> Temperature effects in particular have revealed a glass transition temperature of 6 °C.<ref name="Aldred" />
The number of threads used by a mussel to attach is typically between 20 and 60; this can vary by the species, season, or age of the mussel. Under cyclic tidal conditions, the radial spread of fiber placement allows the mussel to dynamically align most of its fibers in the direction of applied force. This lowers the stress on any one thread, reducing the chances of failure and detachment.<ref name="Bell and Gosline" /> Mussels are also capable of ejecting the entire byssal complex, including the central stem, without damaging themselves. The complex can simply be regenerated, with fibers placement resuming within 24 hours.<ref name="Peyer">{{cite journal |last1=Peyer |first1=Suzanne |title=Zebra mussels anchor byssal threads faster and tighter than quagga mussels in flow |journal=Journal of Experimental Biology |date=23 December 2008 |volume=212 |issue=13 |pages=2027–2036 |doi=10.1242/jeb.028688 |pmid=19525429 |url=https://carollee.labs.wisc.edu/pdfs/Peyer2009.pdf |access-date=9 May 2021|doi-access=free }}</ref>
When a mussel's foot encounters a crevice, it creates a vacuum chamber by forcing out the air and arching up, similar to a plumber's plunger unclogging a drain. The byssus, which is made of keratin, quinone-tanned proteins (polyphenolic proteins), and other proteins, is spewed into this chamber in a liquid form (similar to injection moulding in polymer processing) which then bubbles into a sticky foam. By curling its foot into a tube and pumping the foam, the mussel produces sticky threads each about the size of a human hair. The mussel then varnishes the threads with another protein, resulting in an adhesive.<ref name="Starr" /> The attachment dynamics of the plaque are studied with the goals of artificially replicating the strong adhesive and of developing coatings to which the plaque cannot adhere. Foul release strategies such as fluoropolymer paints and lubricant-infused coatings are an active research area, the aim being to prevent the fouling of marine structures by invasive mussel species such as the zebra and quagga mussel.<ref name="Verma">{{cite journal |last1=Verma |first1=Shatakshi |title=A review on protective polymeric coatings for marine applications |journal=Journal of Coatings Technology and Research |date=20 February 2019 |volume=16 |issue=2 |pages=307–338 |doi=10.1007/s11998-018-00174-2 |s2cid=139442176 |url=https://link.springer.com/article/10.1007/s11998-018-00174-2 |access-date=9 May 2021|url-access=subscription }}</ref>
==Biomimetics== Byssus is a remarkable adhesive, one that is neither degraded nor deformed by water as many synthetic adhesives are.<ref name="Forooshani">{{cite journal |last1=Forooshani |first1=Pegah |last2=Lee |first2=Bruce |title=Recent approaches in designing bioadhesive materials inspired by mussel adhesive protein |journal=Journal of Polymer Science Part A: Polymer Chemistry |date=11 October 2016 |volume=55 |issue=1 |pages=9–33 |doi=10.1002/pola.28368 |pmid=27917020 |pmc=5132118 |doi-access=free }}</ref> The remarkable properties of this adhesive, specifically the mussel foot proteins (Mfps), has spurred many attempts to imitate the excellent adhesive capacity that mussels show, either by producing Mfps via other organisms or by creating synthetic polymers with similar properties. For instance, genetic engineers have inserted mussel DNA into yeast cells to translate the genes into the appropriate proteins.<ref>{{Cite book |author=Robert L. Strausberg |title = Adhesives from Renewable Resources|volume = 385|pages = 453–464|date=31 December 1989 |doi=10.1021/bk-1989-0385.ch032|display-authors=etal|series = ACS Symposium Series|isbn = 978-0-8412-1562-7|chapter = Development of a Microbial System for Production of Mussel Adhesive Protein}}</ref> Synthetic approaches generally utilize catechol as a cross-linking agent to produce wear-resistant polymer networks. Imitation of Mfp-3 to induce coacervation is another key property, as this protects the material from partial dissolution in saltwater.<ref name="Forooshani" />The protein structure of byssus is reminiscent of that of silk produced by insects.<ref>{{Cite journal |last1=Simmons |first1=Miriam |last2=Horbelt |first2=Nils |last3=Sverko |first3=Tara |last4=Scoppola |first4=Ernesto |last5=Jackson |first5=Daniel J. |last6=Harrington |first6=Matthew J. |date=2023-11-28 |title=Invasive mussels fashion silk-like byssus via mechanical processing of massive horizontally acquired coiled coils |journal=Proceedings of the National Academy of Sciences |language=en |volume=120 |issue=48 |article-number=e2311901120 |doi=10.1073/pnas.2311901120 |doi-access=free |issn=0027-8424 |pmc=10691215 |pmid=37983489|bibcode=2023PNAS..12011901S }}</ref> Other examples of biomimetic approaches for creating mussel-inspired adhesives use these polymers as a backbone.<ref>{{Cite journal |last1=Lo Presti |first1=Marco |last2=Rizzo |first2=Giorgio |last3=Farinola |first3=Gianluca M. |last4=Omenetto |first4=Fiorenzo G. |date=August 2021 |title=Bioinspired Biomaterial Composite for All-Water-Based High-Performance Adhesives |journal=Advanced Science |language=en |volume=8 |issue=16 |article-number=e2004786 |doi=10.1002/advs.202004786 |issn=2198-3844 |pmc=8373158 |pmid=34080324}}</ref><ref>{{Cite journal |last1=Lo Presti |first1=Marco |last2=Ostrovsky-Snider |first2=Nicholas |last3=Rizzo |first3=Giorgio |last4=Portoghese |first4=Marina |last5=Blasi |first5=Davide |last6=Farinola |first6=Gianluca M. |last7=Omenetto |first7=Fiorenzo G. |date=2023-08-29 |title=The role of tyrosine in protein-dopamine based bioinspired adhesives: the stoichiometry that maximizes bonding strength |journal=Frontiers in Biomaterials Science |language=English |volume=2 |doi=10.3389/fbiom.2023.1184088 |doi-access=free |issn=2813-3749}}</ref>
Applications of biomimetic byssus adhesive include biomedical adhesives,<ref name="Allen">{{cite journal |last1=Allen |first1=Mark |title=Prospective randomized study evaluating a biodegradable polymeric sealant for sealing intraoperative air leaks that occur during pulmonary resection |journal=The Annals of Thoracic Surgery |date=May 2004 |volume=77 |issue=5 |pages=1792–1801 |doi=10.1016/j.athoracsur.2003.10.049 |pmid=15111188 |url=https://www.sciencedirect.com/science/article/pii/S0003497503021908 |access-date=9 May 2021|url-access=subscription }}</ref> therapeutic applications,<ref name="Black">{{cite journal |last1=Black |first1=Kvar |title=Polydopamine-enabled surface functionalization of gold nanorods for cancer cell-targeted imaging and photothermal therapy |journal=Nanomedicine |date=14 August 2012 |volume=8 |issue=1 |pages=17–28 |doi=10.2217/nnm.12.82 |pmid=22891865 |pmc=3544340 }}</ref> and anti-fouling coatings.<ref name="Dalsin">{{cite journal |last1=Dalsin |first1=Jeffrey |title=Protein Resistance of Titanium Oxide Surfaces Modified by Biologically Inspired mPEG−DOPA |journal=Langmuir |date=9 December 2004 |volume=21 |issue=2 |pages=640–646 |doi=10.1021/la048626g |pmid=15641834 |url=https://pubs.acs.org/doi/10.1021/la048626g |access-date=9 May 2021|url-access=subscription }}</ref>
==Historical uses== "Byssus" often refers to the long, fine, silky threads secreted by the large Mediterranean pen shell, ''Pinna nobilis''. The byssus threads from this ''Pinna'' species can be up to {{cvt|6|cm}} in length and have historically been made into cloth.<ref name="McKinley">{{cite journal |last1=McKinley |first1=Daniel |title=Pinna and Her Silken Beard: A Foray Into Historical Misappropriations |journal=Ars Textrina: A Journal of Textiles and Costumes |date=June 1998 |volume=29 |pages=9–223}}</ref> Byssus cloth is a rare fabric, also known as sea silk, that is made using the byssus of pen shells as the fiber source.<ref name="Maeder">{{cite journal|last=Maeder|first=Felicitas|title=The project Sea-silk: Rediscovering an Ancient Textile Material|journal=Archaeological Textiles Newsletter|date=2002|volume=35|pages=8–11}}</ref><ref name="Hill">{{cite book|last=Hill|first=John|title=Through the Jade Gate to Rome: A Study of the Silk Routes during the Later Han Dynasty, 1st to 2nd centuries CE|date=2009|publisher=Book Surge|location=Charleston, SC|isbn=978-1-4392-2134-1|edition=2nd}}</ref> The byssus of ''Atrina pectinata'', a shell of the same family, has been used in Sardinia as a substitute for critically endangered ''Pinna nobilis'', to weave sea silk.<ref>{{cite magazine |last= Cubello |first= Stefania |date= 2018 |title= From the Soul of the Sea |url= https://muschelseide.ch/wp-content/uploads/2020/02/PP-Sea-Silk_ENG.pdf |magazine= Patek Philippe International Magazine |location= Geneva |publisher= Patek Philippe |pages= 35–39 |access-date= 17 August 2024}}</ref>
''Byssus'' was used by Carl Linnaeus as a genus of plants (some later known to be cyanobacteria). It has little relevance in current taxonomy, as most specimens are either lost or not identified. The ones that are identified have been either synonymized (''B. jolithus'', ''B. aurea'') or turned into ''nomen rejiciendum'' (''B. cryptarum'').<ref>{{cite journal |last1=Ross |first1=R. |last2=Irvine |first2=L. M. |title=The Typification of the Genus Byssus L. (1753) |journal=Taxon |date=June 1967 |volume=16 |issue=3 |pages=184–186 |doi=10.2307/1216985|jstor=1216985 |bibcode=1967Taxon..16..184R }}</ref>
==References== {{Reflist}}
== External links ==
{{Commonscat}} * {{Wiktionary-inline|byssus}}
{{Bivalve anatomy}} {{Fibers}}
Category:Bivalve anatomy Category:Mollusc products