Lancelet

Adult amphioxus typically inhabit the seafloor, burrowing into well-ventilated substrates characterized by a soft texture and minimal organic content. While various species have been observed in different types of substrate, such as fine sand, coarse sand, and shell deposits, most exhibit a distinct preference for coarse sand with low levels of fine particles. For instance, Branchiostoma nigeriense along the west coast of Africa, Branchiostoma caribaeum in Mississippi Sound and along the coast from South Carolina to Georgia, B. senegalense in the Atlantic Ocean on the shelf region off North West Africa, and B. lanceolatum along the Mediterranean coast of southern France all demonstrate this preference.{{Cite journal |last1=Webb |first1=J. E. |last2=Hill |first2=M. B. |last3=Wells |first3=George Philip |date=1958-09-04 |title=The ecology of Lagos Lagoon. IV. On the reactions of Branchiostoma nigeriense Webb to its environment |url=https://royalsocietypublishing.org/doi/10.1098/rstb.1958.0008 |journal=Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences |volume=241 |issue=683 |pages=355–391 |doi=10.1098/rstb.1958.0008|bibcode=1958RSPTB.241..355W |url-access=subscription }}{{Cite journal |last1=Boschung |first1=H.T. |last2=Gunter |first2=G. |title=Distribution and variation of Branchiostoma caribaeum in Mississippi Sound |journal=Tulane Studies of Zoology |publication-date=1962}}{{Cite journal |last=Cory |first=Robert L. |date=1967 |title=Distribution and Ecology of Lancelets (order Amphioxi) Over the Continental Shelf of the Southeastern United States |url=https://aslopubs.onlinelibrary.wiley.com/doi/10.4319/lo.1967.12.4.0650 |journal=Limnology and Oceanography |language=en |volume=12 |issue=4 |pages=650–656 |doi=10.4319/lo.1967.12.4.0650 |bibcode=1967LimOc..12..650C |issn=1939-5590}}{{Cite journal |last1=Gosselck |first1=Fritz |last2=Spittler |first2=Peter |year=1979 |title=Age Structure, Growth, and Weight of Branchiostoma senegalense (Acrania, Branchiostomidae). off North-West Africa |url=https://onlinelibrary.wiley.com/doi/10.1002/iroh.19790640418 |journal=Internationale Revue der gesamten Hydrobiologie und Hydrographie |volume=64 |issue=4 |pages=541–550 |doi=10.1002/iroh.19790640418|url-access=subscription }}{{Cite journal |last1=Caccavale |first1=Filomena |last2=Osca |first2=David |last3=D'Aniello |first3=Salvatore |last4=Crocetta |first4=Fabio |date=2021-05-06 |title=Molecular taxonomy confirms that the northeastern Atlantic and Mediterranean Sea harbor a single lancelet, Branchiostoma lanceolatum (Pallas, 1774) (Cephalochordata: Leptocardii: Branchiostomatidae) |journal=PLOS ONE |language=en |volume=16 |issue=5 |pages=e0251358 |doi=10.1371/journal.pone.0251358 |doi-access=free |issn=1932-6203 |pmc=8101936 |pmid=33956890|bibcode=2021PLoSO..1651358C }}{{Cite journal |last1=Desdevises |first1=Yves |last2=Maillet |first2=Vincent |last3=Fuentes |first3=Michael |last4=Escriva |first4=Hector |date=2011-04-15 |title=A Snapshot of the Population Structure of Branchiostoma lanceolatum in the Racou Beach, France, during Its Spawning Season |journal=PLOS ONE |language=en |volume=6 |issue=4 |pages=e18520 |doi=10.1371/journal.pone.0018520 |doi-access=free |issn=1932-6203 |pmc=3078106 |pmid=21525973|bibcode=2011PLoSO...618520D }} However, Branchiostoma floridae from Tampa Bay, Florida, appears to be an exception to this trend, favoring fine sand bottoms instead.{{Cite journal |last1=Stokes |first1=M. Dale |last2=Holland |first2=Nicholas D. |date=1996 |title=Reproduction of the Florida Lancelet (Branchiostoma floridae): Spawning Patterns and Fluctuations in Gonad Indexes and Nutritional Reserves |url=https://www.jstor.org/stable/3227024 |journal=Invertebrate Biology |volume=115 |issue=4 |pages=349–359 |doi=10.2307/3227024 |jstor=3227024 |bibcode=1996InvBi.115..349S |issn=1077-8306|url-access=subscription }}

Their habitat preference reflects their feeding method: they only expose the front end to the water and filter-feed on plankton by means of a branchial ciliary current that passes water through a mucous sheet. Branchiostoma floridae is capable of trapping particles from microbial to small phytoplankton size,{{Cite journal |last1=Smith|first1=Allison J.| last2= Nash|first2=Troy R. |last3= Ruppert| first3=Edward E.|date=2000|title=The size range of suspended particles trapped and ingested by the filter-feeding lancelet Branchiostoma floridae (Cephalochordata: Acrania)| url= https://www.cambridge.org/core/journals/journal-of-the-marine-biological-association-of-the-united-kingdom/article/div-classtitlethe-size-range-of-suspended-particles-trapped-and-ingested-by-the-filter-feeding-lancelet-span-classitalicbranchiostoma-floridaespan-cephalochordata-acraniadiv/78AD799D990BE3517E0D77BD557580E0|journal=Journal of the Marine Biological Association of the United Kingdom| language= en| volume= 80|issue=2|pages=329–332|issn=1469-7769| doi= 10.1017/S0025315499001903|bibcode=2000JMBUK..80..329R |s2cid=85696980|url-access=subscription}} while B. lanceolatum preferentially traps bigger particles (>4 μm).{{Cite journal|last1=Riisgard|first1=Hans Ulrik|last2=Svane|first2=Ib|date=1999| title= Filter Feeding in Lancelets (Amphioxus), vertebrate Biology| journal= Invertebrate Biology| volume= 118|issue=4|pages=423|doi=10.2307/3227011|issn=1077-8306| jstor= 3227011}}

Lancelets are gonochoric animals, i.e. having two sexes, and they reproduce via external fertilisation. They only reproduce during their spawning season, which varies slightly between species — usually corresponding to spring and summer months.{{Cite journal|last=Escriva|first=Hector|date=2018|title=My Favorite Animal, Amphioxus: Unparalleled for Studying Early Vertebrate Evolution| journal= BioEssays| language= en| volume= 40| issue= 12|pages= 1800130| doi= 10.1002/bies.201800130|pmid=30328120|s2cid=53528269|issn=1521-1878| url=https://hal.sorbonne-universite.fr/hal-01974406/file/83-Escriva-2018-BioEssays_sans%20marque.pdf}} All lancelets species spawn shortly after sunset, either synchronously (e.g. Branchiostoma floridae, about once every two weeks during spawning season{{Cite journal |last1= Stokes|first1=M. Dale| last2= Holland|first2=Nicholas D.| date= 1996| title=Reproduction of the Florida Lancelet (Branchiostoma floridae): Spawning Patterns and Fluctuations in Gonad Indexes and Nutritional Reserves| journal=Invertebrate Biology| volume=115|issue=4|pages=349|doi=10.2307/3227024|issn=1077-8306| jstor=3227024|bibcode=1996InvBi.115..349S }}) or asynchronously (Branchiostoma lanceolatum, gradual spawning through the season{{Cite journal| last1=Fuentes|first1=Michael|last2=Benito|first2=Elia|last3=Bertrand|first3=Stephanie|last4=Paris|first4=Mathilde|last5=Mignardot|first5=Aurelie|last6=Godoy|first6=Laura|last7=Jimenez-Delgado| first7=Senda|last8=Oliveri|first8=Diana|last9=Candiani|first9=Simona|date=2007| display-authors=3| title= Insights into spawning behavior and development of the european amphioxus (Branchiostoma lanceolatum)|journal=Journal of Experimental Zoology Part B: Molecular and Developmental Evolution| language= en| volume= 308B| issue= 4|pages=484–493| doi= 10.1002/jez.b.21179|pmid=17520703|bibcode=2007JEZB..308..484F |issn= 1552-5015}}). Rare instances of hermaphroditism have been reported in Branchiostoma lanceolatum and B. belcheri, where a small number of female gonads were observed within male individuals, typically ranging from 2 to 5 gonads out of a total of 45–50.{{Citation needed|date=June 2025}}

Nicholas and Linda Holland were the first researchers to describe a method of obtaining amphioxus embryos by induction of spawning in captivity and in vitro fertilization.{{Cite journal |title=Fine Structural Study of the Cortical Reaction and Formation of the Egg Coats in a Lancelet|journal = The Biological Bulletin|volume = 176|issue = 2|pages = 111–122| first1= Nicholas D. | last1= Holland | first2= Linda Z. | last2= Holland |doi= 10.2307/1541578| jstor= 1541578|year = 1989|url = https://www.biodiversitylibrary.org/part/10948}} Spawning can be artificially induced in the lab by electric or thermal shock.{{Cite journal| author1=Guang Li |author2=ZongHuang Shu |author3=Yiquan Wang|title=Year-Round Reproduction and Induced Spawning of Chinese Amphioxus, Branchiostoma belcheri, in Laboratory|journal=PLOS ONE| volume= 8|issue =9| pages= e75461| doi= 10.1371/journal.pone.0075461| pmid=24086537|pmc=3784433|year=2013|bibcode=2013PLoSO...875461L|doi-access= free}}

Observations of amphioxus anatomy began in the middle of the 19th century. Alexander Kovalevsky first described the key anatomical features of the adult amphioxus (hollow dorsal nerve tube, endostyle, segmented body, postanal tail).{{Cite book|title=Entwickelungsgeschichte des Amphioxus lanceolatus|last=Kovalevsky AO.|publisher=Mém Acad Sci St Petersburg.|year=1867}} Armand De Quatrefages first completely described the nervous system of amphioxus.{{Cite book|title=Annales des sciences naturelles|last=de Quatrefages|first=Armand|publisher=Libraires-editeurs|year=1845}}

Kovalevsky also released the first complete description of amphioxus embryos, while Max Schultze was the first{{Specify|reason=Needs to be clarified; used to mention Leuckart, but the source by Shultze always mentions him in the same breath as Frey; please check|date=June 2025}} to describe the larvae.{{Cite book|title=Beiträge zur naturgeschichte der turbellarien|last=Schulze|first=Max S.|year=1851|publisher=Koch}}

The first representative organism of the group to be described was Branchiostoma lanceolatum. It was described by Peter Simon Pallas in 1774 as molluscan slugs in the genus Limax.{{cite book | last1 = Pallas | first1 = Peter Simon | year = 1774 | publisher = Gottlieb August Lange | location = Berlin | pages = 41 | title = Spicilegia Zoologica. Fasciculus decimus}} It was not until 1834 that Oronzio Gabriele Costa brought the phylogenetic position of the group closer to the agnathan vertebrates (hagfish and lampreys), including it in the new genus Branchiostoma (from the Greek, branchio = "gills", stoma = "mouth").{{cite book | last1 = Costa | first1 = Oronzio Gabriele | year = 1834 | url = https://books.google.com/books?id=zfNhAAAAcAAJ | publisher = Tipografia di Azzolino e Comp. | location = Naples | pages = 90 | title = Cenni zoologici ossia descrizione sommaria delle specie nuove di animali discoperti in diverse contrade del regno nell' anno 1834}}{{Cite journal | first1 = Jordi | last1 = Garcia-Fernàndez | first2 = Èlia | last2 = Benito-Gutierrez | title = It's a long way from amphioxus: descendants of the earliest chordate | journal = BioEssays | volume = 31 | issue = 6 | pages = 665–675| date = June 2008 | doi = 10.1002/bies.200800110 | pmid=19408244| s2cid = 9292134 }} In 1836, William Yarrell renamed the genus as Amphioxus (from the Greek: "pointed on both sides"),{{cite book | last1 = Yarrell | first1 = William | year = 1836 | url = https://www.biodiversitylibrary.org/item/75546 | publisher = John van Voorst | location = London | pages = 472 | title = A History of British Fishes. Vol. II| volume = 2 }} now considered an obsolete synonym of the genus Branchiostoma. The term "amphioxus" is still used as a common name along with "lancelet", especially in the English language. All extant lancelets are all placed in the family Branchiostomatidae, class Leptocardii, and subphylum Cephalochordata.{{cite WoRMS |author=WoRMS |year=2024 |title=Branchiostomatidae Bonaparte, 1846 |id=196078 |access-date=11 February 2024}}

File:Lancelet Anatomy.png

The larvae are extremely asymmetrical, with the mouth and anus on the left side, and the gill slits on the right side.{{Cite journal |last1=D'Aniello |first1=Salvatore |last2=Bertrand |first2=Stephanie |last3=Escriva |first3=Hector |date=2023-09-18 |editor-last=Pérez Valle |editor-first=Helena |editor2-last=Rodgers |editor2-first=Peter |title=Amphioxus as a model to study the evolution of development in chordates |journal=eLife |volume=12 |pages=e87028 |doi=10.7554/eLife.87028|doi-access=free |pmid=37721204 |pmc=10506793 }}{{Cite journal |last1=Meulemans |first1=Daniel |last2=Bronner-Fraser |first2=Marianne |date=2007-08-29 |title=Insights from amphioxus into the evolution of vertebrate cartilage |journal=PLOS ONE |volume=2 |issue=8 |pages=e787 |doi=10.1371/journal.pone.0000787 |doi-access=free |pmc=1950077 |pmid=17726517|bibcode=2007PLoSO...2..787M }} Organs associated with the pharynx are positioned either exclusively on the left or on the right side of the body. In addition, segmented muscle blocks and parts of the nervous system are asymmetrical.{{Cite journal |last=Soukup |first=Vladimir |date=2017 |title=Left-right asymmetry specification in amphioxus: review and prospects |url=https://pubmed.ncbi.nlm.nih.gov/29319110/ |journal=The International Journal of Developmental Biology |volume=61 |issue=10–11–12 |pages=611–620 |doi=10.1387/ijdb.170251vs |pmid=29319110}} After metamorphosis the anatomy becomes more symmetrical, but some asymmetrical traits are still present also as adults, such as the nervous system and the location of the gonads which are found on the right side in Asymmetron and Epigonichthys (in Branchiostoma gonads develop on both sides of body).{{Cite journal |last1=Kaji |first1=Takao |last2=Aizawa |first2=Shinichi |last3=Uemura |first3=Masanori |last4=Yasui |first4=Kinya |date=2001-07-09 |title=Establishment of left-right asymmetric innervation in the lancelet oral region |url=https://onlinelibrary.wiley.com/doi/10.1002/cne.1039 |journal=Journal of Comparative Neurology |language=en |volume=435 |issue=4 |pages=394–405 |doi=10.1002/cne.1039 |pmid=11406821 }}{{Cite journal |last1=Igawa |first1=Takeshi |last2=Nozawa |first2=Masafumi |last3=Suzuki |first3=Daichi G. |last4=Reimer |first4=James D. |last5=Morov |first5=Arseniy R. |last6=Wang |first6=Yiquan |last7=Henmi |first7=Yasuhisa |last8=Yasui |first8=Kinya |date=2017-04-25 |title=Evolutionary history of the extant amphioxus lineage with shallow-branching diversification |journal=Scientific Reports |language=en |volume=7 |issue=1 |pages=1157 |doi=10.1038/s41598-017-00786-5|pmid=28442709 |pmc=5430900 |bibcode=2017NatSR...7.1157I }}

Depending on the exact species involved, the maximum length of lancelets is typically {{convert|2.5|to(-)|8|cm|in|abbr=on|1}}.{{cite web |author=Barnes, M.K.S |date=7 June 2015 |editor1=Tyler-Walters, H. |editor2=K. Hisc ock |url=http://www.marlin.ac.uk/species/detail/85 |title=Lancelet (Branchiostoma lanceolatum) |publisher=Marine Life Information Network: Biology and Sensitivity Key Information Reviews |access-date=7 January 2018 |df=dmy-all}} Branchiostoma belcheri and B. lanceolatum are among the largest. Except for the size, the species are very similar in general appearance, differing mainly in the number of myotomes and the pigmentation of their larvae. They have a translucent, somewhat fish-like body, but without any paired fins or other limbs. A relatively poorly developed tail fin is present, so they are not especially good swimmers. While they do possess some cartilage material stiffening the gill slits, mouth, and tail, they have no true complex skeleton.{{cite book |author=Romer, Alfred Sherwood |author2=Parsons, Thomas S. |year=1977 |title=The Vertebrate Body |publisher=Holt-Saunders International |location= Philadelphia, PA |pages= 18–21 |isbn=978-0-03-910284-5 |df=dmy-all}}

In common with vertebrates, lancelets have a hollow nerve cord running along the back, pharyngeal slits and a tail that runs past the anus. Also like vertebrates, the muscles are arranged in blocks called myomeres.{{Cite journal |last1=Walker |first1=Warren F. |last2=Noback |first2=Charles R. |date=2021 |title=Muscular system |url=https://www.accessscience.com/content/muscular-system/440200 |journal=Access Science |language=en |doi=10.1036/1097-8542.440200|url-access=subscription }}

Unlike vertebrates, the dorsal nerve cord is not protected by bone but by a simpler notochord made up of a cylinder of cells that are closely packed in collagen fibers to form a toughened rod. The lancelet notochord, unlike the vertebrate spine, extends into the head. This gives the subphylum, Cephalochordata, its name ({{math|κεφαλή}}, kephalē means 'head'). The fine structure of the notochord and the cellular basis of its adult growth are best known for the Bahamas lancelet, Asymmetron lucayanum{{cite journal |last1=Holland |first1=Nicholas |last2=Somorjai |first2=Ildiko |year=2020 |title=Serial blockface SEM suggests that stem cells may participate in adult notochord growth in an invertebrate chordate, the Bahamas lancelet |journal=EvoDevo |volume=11 |issue=22 |page=22 |doi=10.1186/s13227-020-00167-6 |pmid=33088474 |pmc=7568382 |doi-access=free }}

The nerve cord is only slightly larger in the head region than in the rest of the body, so that lancelets do not appear to possess a true brain. However, developmental gene expression and transmission electron microscopy indicate the presence of a diencephalic forebrain, a possible midbrain, and a hindbrain.{{cite journal |last1=Candiani |first1=Simona |last2=Moronti |first2=Luca |last3=Ramoino |first3=Paola |last4=Schubert |first4=Michael |last5=Pestarino |first5=Mario |year=2012 |title=A neurochemical map of the developing amphioxus nervous system |journal=BMC Neuroscience |volume=13 |issue=1 |page=59 |issn=1471-2202 |doi=10.1186/1471-2202-13-59 |pmid=22676056 |pmc=3484041|df=dmy-all |doi-access=free }}{{cite journal |last=Holland |first=L.Z. |year=2015 |title=The origin and evolution of chordate nervous systems |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |volume=370 |issue=1684 |page=20150048 |issn=0962-8436 |doi=10.1098/rstb.2015.0048 |pmid=26554041 |pmc=4650125 |df=dmy-all}} Recent studies involving a comparison with vertebrates indicate that the vertebrate thalamus, pretectum, and midbrain areas jointly correspond to a single, combined region in the amphioxus, which has been termed di-mesencephalic primordium (DiMes).{{cite journal |vauthors = Albuixech-Crespo B, López-Blanch L, Burguera D, Maeso I, Sánchez-Arrones L |display-authors=etal |year=2017 |title=Molecular regionalization of the developing amphioxus neural tube challenges major partitions of the vertebrate brain |journal= PLOS Biology |volume=15 |issue=4 |pages=e2001573 |doi=10.1371/journal.pbio.2001573 |pmid=28422959 |pmc=5396861 |doi-access=free }}

Lancelets have four known kinds of light-sensing structures: Joseph cells, Hesse organs, an unpaired anterior eye and lamellar body, all of which utilize opsins as light receptors. All of these organs and structures are located in the neural tube, with the frontal eye at the front, followed by the lamellar body, the Joseph cells, and the Hesse organs.{{cite book |last1=Nieuwenhuys |first1=Rudolf |author-link1=Rudolf Nieuwenhuys |last2=ten Donkelaar |first2=Hans J. |author3=Charles Nicholson |title=The Central Nervous System of Vertebrates |url=https://books.google.com/books?id=gsDqCAAAQBAJ&pg=PA371 |access-date=25 November 2015 |date=14 November 2014 |publisher=Springer |isbn=978-3-642-18262-4 |page=371 |df=dmy-all}}{{cite book |last=Wanninger |first=Andreas |title=Evolutionary Developmental Biology of Invertebrates 6: Deuterostomia |url=https://books.google.com/books?id=GxZcCgAAQBAJ&pg=PA108 |access-date=21 November 2015 |date=11 August 2015|publisher=Springer |isbn=978-3-7091-1856-6 |pages=93–94, 108–109 |df=dmy-all}}{{cite journal |last1=Lamb |first1=Trevor D.|title=Evolution of phototransduction, vertebrate photoreceptors and retina |journal=Progress in Retinal and Eye Research |volume=36 |year=2013 |pages=52–119 |issn=1350-9462 |doi=10.1016/j.preteyeres.2013.06.001 |pmid=23792002 |s2cid=38219705|df=dmy-all|doi-access=free |hdl=1885/84715 |hdl-access=free }}

Joseph cells are bare photoreceptors surrounded by a band of microvilli. These cells bear the opsin melanopsin. The Hesse organs (also known as dorsal ocelli) consist of a photoreceptor cell surrounded by a band of microvilli and bearing melanopsin, but half enveloped by a cup-shaped pigment cell. The peak sensitivity of both cells is ~470 nm{{cite journal |last1=del Pilar Gomez |first1=M. |last2=Anyfgueyra |first2=J. M. |last3=Nasi|first3=E. |title=Light-transduction in melanopsin-expressing photoreceptors of Amphioxus |journal=Proceedings of the National Academy of Sciences |volume=106 |issue=22 |year=2009 |pages=9081–9086 |issn=0027-8424 |doi=10.1073/pnas.0900708106 |pmid=19451628 |pmc=2690026 |bibcode=2009PNAS..106.9081D |df=dmy-all|doi-access=free }} (blue).

Both the Joseph cells and Hesse organs are in the neural tube, the Joseph cells forming a dorsal column, the Hesse organs in the ventral part along the length of the tube. The Joseph cells extend from the caudal end of the anterior vesicle (or cerebral vesicle) to the boundary between myomeres three and four, where the Hesse organs begin and continue nearly to the tail.{{cite book |last1= Le Douarin |first1=Nicole Marthe|author-link1=Nicole Marthe Le Douarin |last2=Dupin |first2=Elisabeth |editor=Paul Trainor |title=Neural Crest Cells: Evolution, development and disease |url=https://books.google.com/books?id=QckxAQAAQBAJ&pg=PA10 |access-date=25 November 2015 |date=23 November 2013 |publisher=Academic Press |isbn=978-0-12-404586-6 |page=10 |df=dmy-all}}{{cite journal |last1=Wicht |first1=Helmut |last2=Lacalli |first2=Thurston C. |title=The nervous system of amphioxus: Structure, development, and evolutionary significance |journal=Canadian Journal of Zoology |volume=83 |issue=1 |year=2005 |pages=122–150 |issn=0008-4301 |doi=10.1139/z04-163 |bibcode=2005CaJZ...83..122W |df=dmy-all}}

The frontal eye consists of a pigment cup, a group of photoreceptor cells (termed Row 1), three rows of neurons (Rows 2–4), and glial cells. The frontal eye, which expresses the PAX6 gene, has been proposed as the homolog of vertebrate paired eyes,or the pineal eye on vertebrates, the pigment cup as the homolog of the RPE (retinal pigment epithelium), the putative photoreceptors as homologs of vertebrate rods and cones, and Row 2 neurons as homologs of the retinal ganglion cells.{{cite journal |last1=Vopalensky |first1=P. |last2=Pergner |first2=J. |last3=Liegertova |first3=M. |last4=Benito-Gutierrez |first4=E. |last5=Arendt |first5=D. |last6=Kozmik |first6=Z. |title=Molecular analysis of the amphioxus frontal eye unravels the evolutionary origin of the retina and pigment cells of the vertebrate eye |journal=Proceedings of the National Academy of Sciences |volume=109 |issue=38 |date=18 September 2012 |pages=15383–15388 |issn=0027-8424 |doi=10.1073/pnas.1207580109 |pmid=22949670 |pmc=3458357 |bibcode=2012PNAS..10915383V |df=dmy-all|doi-access=free }}

The pigment cup is oriented concave dorsally. Its cells contain the pigment melanin.{{cite book |last=Jankowski |first=Roger |title=The Evo-Devo Origin of the Nose, Anterior Skull Base and Midface |url=https://books.google.com/books?id=tfpGAAAAQBAJ&pg=PA152 |access-date=7 December 2015 |date=19 March 2013 |publisher=Springer Science & Business Media |isbn=978-2-8178-0422-4 |page=152 |df=dmy-all}}

The putative photoreceptor cells, Row 1, are arranged in two diagonal rows, one on either side of the pigment cup, symmetrically positioned with respect to the ventral midline. The cells are flask-shaped, with long, slender ciliary processes (one cilium per cell). The main bodies of the cells lie outside of the pigment cup, while the cilia extend into the pigment cup before turning and exiting. The cells bear the opsin c-opsin 1, except for a few which carry c-opsin 3.{{cite journal |last1=Lacalli |first1=T. C. |title=Frontal Eye Circuitry, Rostral Sensory Pathways and Brain Organization in Amphioxus Larvae: Evidence from 3D Reconstructions |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |volume=351 |issue=1337 |date=29 March 1996 |pages=243–263 |url=http://royalsocietypublishing.org/content/royptb/351/1337/243.full.pdf |issn=0962-8436 |doi=10.1098/rstb.1996.0022 |df=dmy-all |bibcode=1996RSPTB.351..243L |access-date=14 December 2015 |archive-url=https://web.archive.org/web/20181021235426/http://royalsocietypublishing.org/content/royptb/351/1337/243.full.pdf |archive-date=21 October 2018 |url-status=dead }}

The Row 2 cells are serotonergic neurons in direct contact with Row 1 cells. Row 3 and 4 cells are also neurons. Cells of all four rows have axons that project into the left and right ventrolateral nerves. For Row 2 neurons, axon projections have been traced to the tegmental neuropil. The tegmental neuropil has been compared with locomotor control regions of the vertebrate hypothalamus, where paracrine release modulates locomotor patterns such as feeding and swimming.

File:Lancelet GFP.png

Lancelets naturally express green fluorescent proteins (GFP) inside their oral tentacles and near the eye spot.{{Cite journal|last1=Deheyn|first1=Dimitri D.|last2=Kubokawa|first2=Kaoru|last3=McCarthy|first3=James K.|last4=Murakami|first4=Akio|last5=Porrachia|first5=Magali|last6=Rouse|first6=Greg W.|last7=Holland|first7=Nicholas D.|date=2007-10-01|title=Endogenous Green Fluorescent Protein (GFP) in Amphioxus|url=https://www.journals.uchicago.edu/doi/10.2307/25066625|journal=The Biological Bulletin|volume=213|issue=2|pages=95–100|doi=10.2307/25066625|jstor=25066625|pmid=17928516|s2cid=45913388|issn=0006-3185|url-access=subscription}} Depending on the species, it can also be expressed in the tail and gonads, though this is only reported in the Asymmetron genus.{{Cite journal|last1=Yue|first1=Jia-Xing|last2=Holland|first2=Nicholas D.|last3=Holland|first3=Linda Z.|last4=Deheyn|first4=Dimitri D.|date=2016-06-17|title=The evolution of genes encoding for green fluorescent proteins: insights from cephalochordates (amphioxus)|url= |journal=Scientific Reports|language=en|volume=6|issue=1|pages=28350|doi=10.1038/srep28350|issn=2045-2322|pmc=4911609|pmid=27311567|bibcode=2016NatSR...628350Y}} Multiple fluorescent protein genes have been recorded in lancelet species throughout the world. Branchiostoma floridae alone has 16 GFP-encoding genes. However, the GFP produced by lancelets is more similar to GFP produced by copepods than jellyfish (Aequorea victoria).{{cn|date=March 2024}}

It is suspected GFP plays multiple roles with lancelets such as attracting plankton towards their mouth. Considering that lancelets are filter feeders, the natural current would draw nearby plankton into the digestive tract. GFP is also expressed in larvae, signifying it may be used for photoprotection by converting higher energy blue light to less harmful green light.{{cn|date=March 2024}}

File:Lancelet GFP GIF.gif

The fluorescent proteins from lancelets have been adapted for use in molecular biology and microscopy. The [https://www.ncbi.nlm.nih.gov/nuccore/EU482389 yellow fluorescent protein] from Branchiostoma lanceolatum exhibits unusually high quantum yield (~0.95).{{Cite journal|last1=Shaner|first1=Nathan C.|last2=Lambert|first2=Gerard G.|last3=Chammas|first3=Andrew|last4=Ni|first4=Yuhui|last5=Cranfill|first5=Paula J.|last6=Baird|first6=Michelle A.|last7=Sell|first7=Brittney R.|last8=Allen|first8=John R.|last9=Day|first9=Richard N.|last10=Israelsson|first10=Maria|last11=Davidson|first11=Michael W.|date=May 2013|title=A bright monomeric green fluorescent protein derived from Branchiostoma lanceolatum|url= |journal=Nature Methods|language=en|publication-date=24 March 2013|volume=10|issue=5|pages=407–409|doi=10.1038/nmeth.2413|pmid=23524392|pmc=3811051|issn=1548-7105}} It has been engineered into a monomeric green fluorescent protein known as [https://www.fpbase.org/protein/mneongreen/ mNeonGreen], which is the brightest known monomeric green or yellow fluorescent protein.

Lancelets are passive filter feeders, spending most of the time half-buried in sand with only their frontal part protruding.{{cite book |author=Kotpal, R.L. |title=Modern Text Book of Zoology: Vertebrates |year=2008–2009 |edition=3 |isbn=978-81-7133-891-7 |pages=76 |publisher=Rastogi Publications |df=dmy-all}} They eat a wide variety of small planktonic organisms, such as bacteria, fungi, diatoms, and zooplankton, and they will also take detritus.{{cite journal| author1=Carvalho, J.E.| author2=F. Lahaye| author3=M. Schubert| year=2017 | title=Keeping amphioxus in the laboratory: an update on available husbandry methods | journal=Int. J. Dev. Biol. | volume=61 | issue=10–11–12| pages=773–783 | doi=10.1387/ijdb.170192ms | pmid= 29319123| doi-access=free }} Little is known about the diet of the lancelet larvae in the wild, but captive larvae of several species can be maintained on a diet of phytoplankton, although this apparently is not optimal for Asymmetron lucayanum.

Lancelets have oral cirri, thin tentacle-like strands that hang in front of the mouth and act as sensory devices and as a filter for the water passing into the body. Water passes from the mouth into the large pharynx, which is lined by numerous gill-slits. The ventral surface of the pharynx contains a groove called the endostyle, which, connected to a structure known as Hatschek's pit, produces a film of mucus. Ciliary action pushes the mucus in a film over the surface of the gill slits, trapping suspended food particles as it does so. The mucus is collected in a second, dorsal groove, known as the epipharyngeal groove, and passed back to the rest of the digestive tract. Having passed through the gill slits, the water enters an atrium surrounding the pharynx, then exits the body via the atriopore.

Both adults and larvae exhibit a "cough" reflex to clear the mouth or throat of debris or items too large to swallow. In larvae the action is mediated by the pharyngeal muscles while in the adult animal it is accomplished by atrial contraction.{{cite book |author1=Rogers, Lesley J. |author2=Andrew, Richard |title=Comparative Vertebrate Lateralization |url=https://books.google.com/books?id=lbS86Sx9tLMC&pg=PA72 |date=25 March 2002 |publisher=Cambridge University Press|isbn=978-1-139-43747-9 |pages=72 ff |df=dmy-all}}{{cite journal|last1=Rigon|first1=Francesca |last2=Stach |first2=Thomas |last3=Caicci |first3=Federico |last4=Gasparini |first4=Fabio |last5=Burighel |first5=Paolo |last6=Manni |first6=Lucia |title=Evolutionary diversification of secondary mechanoreceptor cells in tunicata |journal=BMC Evolutionary Biology |volume=13 |issue=1 |year=2013 |pages=112 |issn=1471-2148 |doi=10.1186/1471-2148-13-112 |pmid=23734698 |pmc=3682859 |df=dmy-all |doi-access=free |bibcode=2013BMCEE..13..112R }}

The remainder of the digestive system consists of a simple tube running from the pharynx to the anus. The hepatic caecum, a single blind-ending caecum, branches off from the underside of the gut, with a lining able to phagocytize the food particles, a feature not found in vertebrates. Although it performs many functions of a liver, it is not considered a true liver but a homolog of the vertebrate liver.{{cite journal |last1=Yuan |first1=Shaochun |last2=Ruan |first2=Jie |last3=Huang |first3=Shengfeng |last4=Chen |first4=Shangwu |last5=Xu |first5=Anlong |title=Amphioxus as a model for investigating evolution of the vertebrate immune system |journal=Developmental & Comparative Immunology |volume=48 |issue=2 |date=February 2015 |pages=297–305 |url=http://mosas.sysu.edu.cn/lab/refsys/uppdf/201462021511673499.pdf |issn=0145-305X |doi=10.1016/j.dci.2014.05.004 |pmid=24877655 |df=dmy-all |access-date=2015-12-16 |archive-url=https://web.archive.org/web/20151222131815/http://mosas.sysu.edu.cn/lab/refsys/uppdf/201462021511673499.pdf |archive-date=2015-12-22 |url-status=dead }}{{cite journal |last1=Yu |first1=Jr-Kai Sky |last2=Lecroisey |first2=Claire |last3=Le Pétillon |first3=Yann |last4=Escriva |first4=Hector |last5=Lammert |first5=Eckhard |last6=Laudet |first6=Vincent |title=Identification, Evolution and Expression of an Insulin-Like Peptide in the Cephalochordate Branchiostoma lanceolatum |journal=PLOS ONE |volume=10 |issue=3 |year=2015 |pages=e0119461 |issn=1932-6203 |doi=10.1371/journal.pone.0119461 |pmid=25774519 |pmc=4361685 |bibcode=2015PLoSO..1019461L |df=dmy-all|doi-access=free }}{{cite journal |last1=Escriva |first1=Hector |last2=Chao |first2=Yeqing |last3=Fan |first3=Chunxin |last4=Liang |first4=Yujun |last5=Gao |first5=Bei |last6=Zhang |first6=Shicui |title=A Novel Serpin with Antithrombin-Like Activity in Branchiostoma japonicum: Implications for the Presence of a Primitive Coagulation System |journal=PLOS ONE |volume=7 |issue=3 |year=2012 |pages=e32392 |issn=1932-6203 |doi=10.1371/journal.pone.0032392 |pmid=22427833 |pmc=3299649 |bibcode=2012PLoSO...732392C |df=dmy-all|doi-access=free }}

Lancelets have no respiratory system, breathing solely through their skin, which consists of a simple epithelium. Despite the name, little if any respiration occurs in the "gill" slits, which are solely devoted to feeding. The circulatory system does resemble that of primitive fish in its general layout, but is much simpler, and does not include a heart. There are no blood cells, and no hemoglobin.

The excretory system consists of segmented "kidneys" containing protonephridia instead of nephrons, and quite unlike those of vertebrates. Also unlike vertebrates, there are numerous, segmented gonads.

Lancelets became famous in the 1860s when Ernst Haeckel began promoting them as a model for the ancestor of all vertebrates. By 1900, lancelets had become a model organism. By the mid-20th century they had fallen out of favor for a variety of reasons, including a decline of comparative anatomy and embryology, and due to the belief that lancelets were more derived than they appeared, e.g., the profound asymmetry in the larval stage.{{cite journal|last1=Hopwood|first1=Nick|title=The cult of amphioxus in German Darwinism; or, Our gelatinous ancestors in Naples' blue and balmy bay|journal=History and Philosophy of the Life Sciences|volume=36|issue=3|date=January 2015|pages=371–393|issn=0391-9714|doi=10.1007/s40656-014-0034-x|pmid=26013195|pmc=4286652}}{{RefTudgeVariety}} More recently, the fundamental symmetric and twisted development of vertebrates is the topic of the axial twist theory. According to this theory, there is a deep agreement between the vertebrates and cephalochordates, and even all chordates.{{cite journal | first1=M.H.E. | last1=de Lussanet | first2=J.W.M. | last2=Osse | year=2012 | title=An ancestral axial twist explains the contralateral forebain and the optic chiasm in vertebrates | journal=Animal Biology | volume=62 | issue=2 | pages=193–216 | doi=10.1163/157075611X617102 | arxiv=1003.1872 | s2cid=7399128}}{{cite journal | first1=M. | last1=Kinsbourne | s2cid=11646580 | title=Somatic twist: a model for the evolution of decussation | journal=Neuropsychology | volume=27 | issue=5 | year=2013 | pages=511–515 | doi=10.1037/a0033662 | pmid=24040928}}

With the advent of molecular genetics lancelets are once again regarded as a model of vertebrate ancestors, and are used again as a model organism.{{cite journal|last1=Holland|first1=L.Z.|last2=Laudet|first2=V.|last3=Schubert|first3=M.|title=The chordate amphioxus: an emerging model organism for developmental biology|journal=Cellular and Molecular Life Sciences|volume=61|issue=18|date=September 2004|pages=2290–2308 |url=https://www.researchgate.net/publication/8337108|issn=1420-682X|doi=10.1007/s00018-004-4075-2|pmid=15378201|pmc=11138525 |s2cid=28284725}}

As a result of their use in science, methods of keeping and breeding lancelets in captivity have been developed for several of the species, initially the European Branchiostoma lanceolatum, but later also the West Pacific Branchiostoma belcheri and Branchiostoma japonicum, the Gulf of Mexico and West Atlantic Branchiostoma floridae and the circumtropical (however, genetic evidence suggest the Atlantic and Indo-Pacific populations should be recognized as separate) Asymmetron lucayanum.{{cite web | url=http://www.embrc-france.fr/en/our-services/supply-biological-resources/model-organisms/amphioxus-branchiostoma-lanceolatum |title=Amphioxus Branchiostoms lanceolatum | publisher=EMBRC France |access-date=7 January 2018 }} They can reach an age of up to 7–8 years.

The animals are edible and harvested in some parts of the world. They are eaten both fresh, tasting like herring, and as a food additive in dry form after being roasted in oil.{{Cn|date=February 2023}} When their gonads start to ripen in the spring it affects their flavor, making them taste bad during their breeding season.{{Cite journal |last1=Holland |first1=Nicholas |last2=Stokes |first2=M. Dale |date=1998 |title=The Lancelet |url=https://www.researchgate.net/publication/241302129|journal=American Scientist |language=en |volume=86 |issue=6 |pages=552 |doi=10.1511/1998.6.552|bibcode=1998AmSci..86..552S }}

File:Amphioxus.png

The lancelets were traditionally seen as the sister lineage to the vertebrates; in turn, these two groups together (sometimes called Notochordata) were considered the sister group to the Tunicata (also called Urochordata and including sea squirts). Consistent with this view, at least ten morphological features are shared by lancelets and vertebrates, but not tunicates.Michael J. Benton (2005). Vertebrate Palaeontology, Third Edition 8. Oxford: Blackwell Publishing. {{ISBN|0-632-05637-1}}. Newer research suggests this pattern of evolutionary relationship is incorrect. Extensive molecular phylogenetic analysis has shown convincingly that the Cephalochordata is the most basal subphylum of the chordates, with tunicates being the sister group of the vertebrates.{{Cite journal |first1=Frédéric |last1=Delsuc |first2=Henner |last2=Brinkmann |first3=Daniel |last3=Chourrout |first4=Hervé |last4=Philippe |url=http://worldcat.org/oclc/784007344|title=Tunicates and not cephalochordates are the closest living relatives of vertebrates.|journal=Nature|year=2006|volume=439|issue=7079|pages=965–8|doi=10.1038/nature04336|pmid=16495997|bibcode=2006Natur.439..965D|s2cid=4382758|oclc=784007344}}{{Cite journal|last1=Putnam|first1=N. H.|last2=Butts|first2=T.|last3=Ferrier|first3=D. E. K.|last4=Furlong|first4=R. F.|last5=Hellsten|first5=U.|last6=Kawashima|first6=T.|last7=Robinson-Rechavi|first7=M.|last8=Shoguchi|first8=E.|last9=Terry|first9=A.|date=Jun 2008|title=The amphioxus genome and the evolution of the chordate karyotype|journal=Nature|volume=453|issue=7198|pages=1064–1071|bibcode=2008Natur.453.1064P|doi=10.1038/nature06967|issn=0028-0836|pmid=18563158|last10=Yu|first10=J. K.|last11=Benito-Gutiérrez|first11=E. L.|last12=Dubchak|first12=I.|last13=Garcia-Fernàndez|first13=J.|last14=Gibson-Brown|first14=J. J.|last15=Grigoriev|first15=I. V.|last16=Horton|first16=A. C.|last17=De Jong|first17=P. J.|last18=Jurka|first18=J.|last19=Kapitonov|first19=V. V.|last20=Kohara|first20=Y.|last21=Kuroki|first21=Y.|last22=Lindquist|first22=E.|last23=Lucas|first23=S.|last24=Osoegawa|first24=K.|last25=Pennacchio|first25=L. A.|last26=Salamov|first26=A. A.|last27=Satou|first27=Y.|last28=Sauka-Spengler|first28=T.|last29=Schmutz|first29=J.|last30=Shin-i|first30=T.|s2cid=4418548|doi-access=free}} This revised phylogeny of chordates suggests that tunicates have secondarily lost some of the morphological characters that were formerly considered to be synapomorphies (shared, derived characters) of vertebrates and lancelets. Lancelets have turned out to be among the most genetically diverse animals sequenced to date, due to high rates of genetic changes like exon shuffling and domain combination.

Among the three extant (living) genera, Asymmetron is basal. Molecular clock studies have come to different conclusions on their divergence, with some suggesting that Asymmetron diverged from other lancelets more than 100 million years ago while others have suggested that it occurred about 46 million years ago. According to the younger estimation, Branchiostoma and Epigonichthys have been estimated to have diverged from each other about 38.3 million years ago. Despite this deep separation, hybrids between Asymmetron lucayanum and Branchiostoma floridae are viable (among the deepest split species known to be able to produce such hybrids).

The following are the species recognised by WoRMS. Other sources recognize about thirty species.{{cite web | author=WoRMS Editorial Board | title= World Register of Marine Species- Cephalochordates species list | year=2013 | url=http://www.marinespecies.org/aphia.php?p=taxlist&pid=1824&rComp=%3E%3D&tRank=220 | access-date=2013-10-22 }} It is likely that currently unrecognized cryptic species remain.

• Class Leptocardii
• Family Branchiostomatidae Bonaparte 1846
• Genus Asymmetron Andrews 1893 [Amphioxides Gill 1895]
• Asymmetron inferum Nishikawa 2004
• Asymmetron lucayanum Andrews 1893 (Sharptail lancelet)
• Genus Branchiostoma Costa 1834 non Newport 1845 non Banks 1905 [Amphioxus Yarrell 1836; Limax Pallas 1774 non Linnaeus 1758 non Férussac 1819 non Martyn 1784; Dolichorhynchus Willey 1901 non Mulk & Jairajpuri 1974]
• Branchiostoma africae Hubbs 1927
• Branchiostoma arabiae Webb 1957
• Branchiostoma bazarutense Gilchrist 1923
• Branchiostoma belcheri (Gray 1847) (Belcher's lancelet)
• Branchiostoma bennetti Boschung & Gunter 1966 (Mud lancelet)
• Branchiostoma bermudae Hubbs 1922
• Branchiostoma californiense Andrews 1893 (Californian lancelet)
• Branchiostoma capense Gilchrist 1902
• Branchiostoma caribaeum Sundevall 1853 (Caribbean lancelet)
• Branchiostoma elongatum (Sundevall 1852)
• Branchiostoma floridae Hubbs 1922 (Florida lancelet)
• Branchiostoma gambiense Webb 1958
• Branchiostoma indicum (Willey 1901)
• Branchiostoma japonicum (Willey 1897) (Pacific lancelet)
• Branchiostoma lanceolatum (Pallas 1774) (European lancelet)
• Branchiostoma leonense Webb 1956
• Branchiostoma longirostrum Boschung 1983 (Shellhash lancelet)
• Branchiostoma malayanum Webb 1956
• Branchiostoma moretonense Kelly 1966; nomen dubium{{cite web|url=http://www.marinespecies.org/urmo/aphia.php?p=taxdetails&id=266214|title=UNESCO-IOC Register of Marine Organisms (URMO) - Branchiostoma mortonense Kelly, 1966}}{{cite web|url=http://www.marinespecies.org/aphia.php?p=taxdetails&id=266214|title=WoRMS - World Register of Marine Species - Branchiostoma mortonense Kelly, 1966}}
• Branchiostoma nigeriense Webb 1955
• Branchiostoma platae Hubbs 1922
• Branchiostoma senegalense Webb 1955
• Branchiostoma tattersalli Hubbs 1922
• Branchiostoma virginiae Hubbs 1922 (Virginian lancelet)
• Genus Epigonichthys Peters 1876 [Amphipleurichthys Whitley 1932; Bathyamphioxus Whitley 1932; Heteropleuron Kirkaldy 1895; Merscalpellus Whitley 1932; Notasymmetron Whitley 1932; Paramphioxus Haekel 1893; Zeamphioxus Whitley 1932]
• Epigonichthys australis (Raff 1912)
• Epigonichthys bassanus (Günther 1884)
• Epigonichthys cingalensis (Kirkaldy 1894); nomen dubium{{cite web |url=http://www.marinespecies.org/aphia.php?p=taxdetails&id=104903 |title=WoRMS - World Register of Marine Species - Epigonichthys Peters, 1876}}
• Epigonichthys cultellus Peters 1877
• Epigonichthys hectori (Benham 1901) (Hector's lancelet)
• Epigonichthys maldivensis (Foster Cooper 1903)

The cladogram presented here illustrates the phylogeny (family tree) of lancelets, and follows a simplified version of the relationships found by Igawa and colleagues (2017):

{{clade|{{clade

|1= Olfactores 60px

| label2= Lancelet? |sublabel2=518 mya ?

| 2={{clade

|state1=dashed

| 1= {{extinct}}Cathaymyrus? († 518 mya)80px

|state2=dashed

| 2= {{extinct}}Palaeobranchiostoma? († 273.01 mya) 70px

| label3=Lancelet (crown group) |sublabel3= 46.0 mya

| 3={{clade

| label1=Asymmetron |sublabel1=16.4 mya

| 1={Asymmetron}

| 2={{clade

| label1=Epigonichthys |sublabel1=27.0 mya

| 1={Epigonichthys}

| label2=Branchiostoma |sublabel2=28.7 mya

| 2={Branchiostoma}

}}

}}

}}

}}|style=font-size:100%;line-height:100%|label1=Chordata|targetA={Asymmetron}|subcladeA={{clade hidden |id=1 |mode=left

|1=Asymmetron inferum

|2=Asymmetron lucayanum 70 px

|3=Asymmetron maldivense

}}|subcladeB={{clade hidden |id=2 |mode=left

|1=Epigonichthys cultellus 75 px

|2=Epigonichthys maldivensis

}}|targetB={Epigonichthys}|targetC={Branchiostoma}|subcladeC={{clade hidden |id=3 |mode=left

|1={{clade

|1=Branchiostoma lanceolatum 70 px

|2=Branchiostoma floridae

}}

|2={{clade

|1=Branchiostoma japonicum 50 px

|2=Branchiostoma belcheri

}}

}}

}}

• Phylliroe

{{reflist|20em}}

• {{cite book |author1=Stach, T.G. |year=2004 |section=Cephalochordata (Lancelets) |editor1=M. Hutchins |editor2=Garrison, R.W. |editor3=Geist, V. |editor4=Loiselle, P.V. |editor5=Schlager, N. |editor6=McDade, M.C. |editor7=Duellman, W.E. |title=Grzimek's Animal Life Encyclopedia |title-link=Grzimek's Animal Life Encyclopedia |edition=2nd |volume=1 |pages=485–493 |place=Detroit, MI |publisher=Gale}}
• {{cite journal |author1=Stokes, M.D. |author2=Holland, N.D. |year=1998 |title=The Lancelet |journal=American Scientist |volume=86 |issue=6 |pages=552–560|doi=10.1511/1998.43.799 }}

{{Commons category|Amphioxiformes}}

{{Wikispecies|Cephalochordata}}

• {{cite web

|title=Cephalochordata

|place=Berkeley, CA

|department=Museum of Paleontology

|publisher=U.C. Berkeley

|url=http://www.ucmp.berkeley.edu/chordata/cephalo.html

}}

• {{cite web

|title=Branchiostoma japonicum and B. belcheri are Distinct Lancelets (Cephalochordata) in Xiamen Waters in China

|website=

|url=https://www.researchgate.net/publication/6935781

|via=ResearchGate

}}

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}}

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}}

• {{cite press release

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}}

• {{YouTube

|id=ycHJMXUT2o0

|title= A movie of the amphioxus embryonic development

}}

• {{cite press release

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}}

• {{cite EB9 |wstitle = Amphioxus |volume= I | page=774 |short=1}}
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|title=Amphioxus: Taxonomy, brief facts, life cycle and embryology

|website=GeoChemBio

|url=http://www.geochembio.com/biology/organisms/lancelet/

}}

• {{UCSC genomes|braFlo1}}

{{Evolution of fish}}

{{Animalia}}

{{Chordata}}

{{Taxonbar|from1=Q1156226|from2=Q20722244|from3=Q21286775|from4=Q2747865|from5=Q61882392}}