# Lancelet

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Subphylum of chordates

Not to be confused with [Lancet](/source/Lancet_(disambiguation)) or [Lancelot](/source/Lancelot).

Cephalochordata (Lancelets) Temporal range: Recent PreꞒ Ꞓ O S D C P T J K Pg N Possible Cambrian[1] and Permian records Branchiostoma lanceolatum Scientific classification Kingdom: Animalia Phylum: Chordata Subphylum: Cephalochordata Haeckel, 1866[3] Class: Leptocardii Müller, 1845[2] Genera †Cathaymyrus? †Palaeobranchiostoma? Branchiostomatidae Bonaparte, 1846[4] Asymmetron Branchiostoma Epigonichthys Synonyms Subphylum or class: Acrania Haeckel, 1866 Order: Amphioxi Bonaparte, 1846[4] Amphioxiformes Berg, 1937[5] Branchiostomiformes Fowler, 1947[6] Family: Amphioxidae Gray, 1842[7] Asymmetrontidae Whitley, 1932[8] Epigonichthyidae Hubbs, 1922[9]

The **lancelets** ([/ˈlænslɪt, ˈlɑːn-/](https://en.wikipedia.org/wiki/Help:IPA/English) [*LA(H)N-slit*](https://en.wikipedia.org/wiki/Help:Pronunciation_respelling_key)), also known as **amphioxi** (sing.: **amphioxus** [/ˌæmfiˈɒksəs/](https://en.wikipedia.org/wiki/Help:IPA/English) [*AM-fee-OK-səs*](https://en.wikipedia.org/wiki/Help:Pronunciation_respelling_key)), consist of 32 described species of somewhat fish-like [benthic](/source/Benthic_zone) [filter-feeding](/source/Filter-feeding) [chordates](/source/Chordate)[10] in the subphylum **Cephalochordata**, class **Leptocardii**, and family **Branchiostomatidae**.[11]

Lancelets diverged from other chordates during or prior to the [Cambrian](/source/Cambrian) period. A number of fossil chordates have been suggested to be closely related to lancelets, including *[Pikaia](/source/Pikaia)* and *[Cathaymyrus](/source/Cathaymyrus)* from the Cambrian and *[Palaeobranchiostoma](/source/Palaeobranchiostoma)* from the [Permian](/source/Permian), but their close relationship to lancelets has been doubted by other authors.[12][13] [Molecular clock](/source/Molecular_clock) analysis suggests that modern lancelets probably diversified much more recently, during the [Cretaceous](/source/Cretaceous) or [Cenozoic](/source/Cenozoic).[14][15]

They are of interest to [zoologists](/source/List_of_authors_of_names_published_under_the_ICZN) as lancelets contain many organs and organ systems that are [homologous](/source/Homology_(biology)) to those of modern fish. Therefore, they provide a number of examples of possible evolutionary [exaptation](/source/Exaptation). For example, the gill-slits of lancelets are used for feeding only, and not for respiration. The circulatory system carries food throughout their body, but does not have [red blood cells](/source/Red_blood_cells) or [hemoglobin](/source/Hemoglobin) for transporting oxygen.

Comparing the [genomes](/source/Genomes) of lancelets and vertebrates and their differences in gene expression, function, and number can shed light on the origins of vertebrates and their [evolution](/source/Evolution).[16] The genome of a few species in the genus *[Branchiostoma](/source/Branchiostoma)* have been sequenced: *B. floridae,*[17] *B. belcheri*,[18] and *B. lanceolatum*.[19]

In Asia, lancelets are harvested commercially as food for humans. In Japan, the amphioxus (*B. belcheri*) has been listed in the registry of "Endangered Animals of Japanese Marine and Fresh Water Organisms".[20]

## Ecology

### Habitat

Adult amphioxi 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 the [Mississippi Sound](/source/Mississippi_Sound) and along the coast from South Carolina to Georgia, *B. senegalense* in the Atlantic Ocean on the [shelf](/source/Continental_shelf) region off [North West Africa](/source/Maghreb), and *B. lanceolatum* along the Mediterranean coast of southern France all demonstrate this preference.[21][22][23][24][25][26] However, *Branchiostoma floridae* from [Tampa Bay](/source/Tampa_Bay), Florida, appears to be an exception to this trend, favoring fine sand bottoms instead.[27]

### Feeding

Their habitat preference reflects their feeding method: they only expose their front ends to the water and filter-feed on [plankton](/source/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,[28] while *B. lanceolatum* preferentially traps bigger particles (>4 μm).[29]

### Reproduction and spawning

Lancelets are [gonochoric](/source/Gonochorism) animals, i.e. having two sexes, and they reproduce via external [fertilisation](/source/Fertilisation). They only reproduce during their [spawning](/source/Spawn_(biology)) season, which varies slightly between species — usually corresponding to spring and summer months.[30] All lancelets species spawn shortly after sunset, either synchronously (e.g. *Branchiostoma floridae*, about once every two weeks during spawning season[31]) or asynchronously (*Branchiostoma lanceolatum*, gradual spawning through the season[32]). Rare instances of [hermaphroditism](/source/Hermaphrodite) 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](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

Nicholas and [Linda Holland](/source/Linda_Holland) were the first researchers to describe a method of obtaining amphioxus embryos by induction of spawning in captivity and in vitro fertilization.[33] Spawning can be artificially induced in the lab by electric or thermal shock.[34]

## History

The first representative organism of the group to be described was *[Branchiostoma lanceolatum](/source/Branchiostoma_lanceolatum)*. It was described by [Peter Simon Pallas](/source/Peter_Simon_Pallas) in 1774 as a [molluscan](/source/Mollusc) slug in the genus *[Limax](/source/Limax)*.[35] It was not until 1834 that [Oronzio Gabriele Costa](/source/Oronzio_Gabriele_Costa) brought the phylogenetic position of the group closer to the [agnathan vertebrates](/source/Agnatha) ([hagfish](/source/Hagfish) and [lampreys](/source/Lampreys)), including it in the new genus *[Branchiostoma](/source/Branchiostoma)* (from the Greek, *branchio-* = "gills", *-stoma* = "mouth").[36][37] In 1836, [William Yarrell](/source/William_Yarrell) renamed the genus as *Amphioxus* (from the Greek: "pointed on both sides"),[38] now considered an obsolete [synonym](/source/Synonym_(taxonomy)) of the genus *Branchiostoma*. The term "amphioxus" is still used as a [common name](/source/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.[39]

Observations of amphioxus anatomy began in the middle of the 19th century. [Alexander Kovalevsky](/source/Alexander_Kovalevsky) first described the key anatomical features of the adult amphioxus (hollow [dorsal nerve tube](/source/Dorsal_nerve_cord), [endostyle](/source/Endostyle), segmented body, post-anal tail).[40] [Armand De Quatrefages](/source/Jean_Louis_Armand_de_Quatrefages_de_Br%C3%A9au) first completely described the nervous system of amphioxus.[41]

Kovalevsky also released the first complete description of amphioxus embryos,[40] while [Max Schultze](/source/Max_Schultze) was the first[*[specify](https://en.wikipedia.org/wiki/Wikipedia:Citing_sources)*] to describe the larvae.[42]

## Anatomy

Anatomy of the lancelet

The larvae are extremely asymmetrical, with the mouth and anus on the left side, and the gill slits on the right side.[43][44] 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.[45] 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 the [genera](/source/Genera) *[Asymmetron](/source/Asymmetron)* and *[Epigonichthys](/source/Epigonichthys)* (in *Branchiostoma*, gonads develop on both sides of body).[46][47]

Depending on the exact species involved, the maximum length of lancelets is typically 2.5 to 8 cm (1.0–3.1 in).[48][49] *Branchiostoma belcheri* and *[B. lanceolatum](/source/Branchiostoma_lanceolatum)* are among the largest.[48] Except for the size, the species are very similar in general appearance, differing mainly in the number of [myotomes](/source/Myotome) and the pigmentation of their larvae.[48] 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](/source/Cartilage) material stiffening the [gill slits](/source/Gill_slit), mouth, and tail, they have no true complex skeleton.[50]

### Nervous system and notochord

In common with vertebrates, lancelets have a hollow nerve cord running along the back, [pharyngeal slits](/source/Pharyngeal_slit) and a tail that runs past the anus. Also like vertebrates, the muscles are arranged in blocks called [myomeres](/source/Myomere).[51]

Unlike vertebrates, the dorsal nerve cord is not protected by bone but by a simpler [notochord](/source/Notochord) made up of a [cylinder](/source/Cylinder_(geometry)) of [cells](/source/Cell_(biology)) that are closely packed in collagen fibers to form a toughened rod. The lancelet notochord, unlike the vertebrate [spine](/source/Vertebral_column), extends into the head. This gives the subphylum *Cephalochordata* its name (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*[52]

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](/source/Transmission_electron_microscopy) indicate the presence of a [diencephalic](/source/Diencephalic) [forebrain](/source/Forebrain), a possible [midbrain](/source/Midbrain), and a [hindbrain](/source/Hindbrain).[53][54] Recent studies involving a comparison with vertebrates indicate that the vertebrate [thalamus](/source/Thalamus), [pretectum](/source/Pretectum), and midbrain areas jointly correspond to a single, combined region in the amphioxus, which has been termed *di-mesencephalic primordium* (DiMes).[55]

### Visual system

Lancelets have four known kinds of light-sensing structures: Three are respectively called *Joseph cells*, *Hesse organs* and *lamellar body*.[*[further explanation needed](https://en.wikipedia.org/wiki/Wikipedia:Please_clarify)*] The fourth is an unpaired anterior eye. All of them utilize [opsins](/source/Opsin) 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*.[56][48][57]

#### *Joseph cells* and *Hesse organs*

Joseph cells are bare photoreceptors surrounded by a band of [microvilli](/source/Microvilli). These cells bear the opsin [melanopsin](/source/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[58] (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.[59][60]

#### Frontal eye

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](/source/Glial_cells). The frontal eye, which expresses the [PAX6](/source/PAX6) gene, has been proposed as the homolog of either the paired eyes or the [pineal eye](/source/Parietal_eye) on vertebrates, the pigment cup as the homolog of the RPE ([retinal pigment epithelium](/source/Retinal_pigment_epithelium)), the putative photoreceptors as homologs of vertebrate [rods](/source/Rod_cell) and [cones](/source/Cone_cell), and Row 2 neurons as homologs of the [retinal ganglion cells](/source/Retinal_ganglion_cells).[61] The pigment cup is oriented concave dorsally. Its cells contain the pigment [melanin](/source/Melanin).[61][62]

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*.[61][63]

The Row 2 cells are [serotonergic](/source/Serotonin) neurons in direct contact with Row 1 cells. Row 3 and 4 cells are also neurons. Cells of all four rows have [axons](/source/Axons) that project into the left and right ventrolateral nerves. For Row 2 neurons, axon projections have been traced to the [tegmental](/source/Tegmentum) [neuropil](/source/Neuropil). The tegmental neuropil has been compared with [locomotor](/source/Animal_locomotion) control regions of the vertebrate [hypothalamus](/source/Hypothalamus), where [paracrine](/source/Paracrine) release modulates locomotor patterns such as feeding and swimming.[61]

### Fluorescent proteins

Green fluorescence in Lancelets. (a. *Branchiostoma floridae* GFP near the eye spot and in the oral tentacles.) (b. *Asymmetron lucayanum* green fluorescence in the gonads.)

Lancelets naturally express [green fluorescent proteins](/source/Green_fluorescent_protein) (GFP) inside their oral tentacles and near the eye spot.[64] Depending on the species, it can also be expressed in the tail and [gonads](/source/Gonad), though this is only reported in the *Asymmetron* genus.[65] Multiple fluorescent protein [genes](/source/Gene) have been recorded in lancelet species throughout the world. *[Branchiostoma floridae](/source/Branchiostoma_floridae)* alone has 16 GFP-encoding genes. However, the GFP produced by lancelets is more similar to GFP produced by [copepods](/source/Copepod) than jellyfish (*[Aequorea victoria](/source/Aequorea_victoria)*).[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

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](/source/Larva), signifying it may be used for [photoprotection](/source/Photoprotection) by converting higher energy blue light to less harmful green light.[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

Live lancelet (*B. floridae*) under a fluorescent microscope.

The fluorescent proteins from lancelets have been adapted for use in molecular biology and microscopy. The [yellow fluorescent protein](https://www.ncbi.nlm.nih.gov/nuccore/EU482389) from *[Branchiostoma lanceolatum](/source/Branchiostoma_lanceolatum)* exhibits unusually high [quantum yield](/source/Quantum_yield) (~0.95).[66] It has been [engineered](/source/Genetic_engineering) into a [monomeric](/source/Monomer) green fluorescent protein known as [mNeonGreen](https://www.fpbase.org/protein/mneongreen/), which is the brightest known monomeric green or yellow fluorescent protein.

### Feeding and digestive system

Lancelets are passive [filter feeders](/source/Filter_feeder),[15] spending most of the time half-buried in sand with only their frontal part protruding.[67] They eat a wide variety of small [planktonic](/source/Plankton) organisms, such as bacteria, [fungi](/source/Fungi), [diatoms](/source/Diatom), and [zooplankton](/source/Zooplankton), and they will also take [detritus](/source/Detritus).[68] Little is known about the diet of the lancelet [larvae](/source/Larvae) in the wild, but captive larvae of several species can be maintained on a diet of [phytoplankton](/source/Phytoplankton), although this apparently is not optimal for *Asymmetron lucayanum*.[68]

Lancelets have oral cirri, thin [tentacle](/source/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](/source/Human_pharynx), which is lined by numerous gill-slits. The ventral surface of the pharynx contains a groove called the [endostyle](/source/Endostyle), which, connected to a structure known as [Hatschek's pit](/source/Hatschek's_pit), produces a film of [mucus](/source/Mucus). [Ciliary](/source/Cilium) 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](/source/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.[50]

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.[69][70]

The remainder of the digestive system consists of a simple tube running from the pharynx to the anus. The [hepatic caecum](/source/Hepatic_caecum), a single blind-ending [caecum](/source/Cecum), branches off from the underside of the gut, with a lining able to [phagocytize](/source/Phagocytosis) 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](/source/Homology_(biology)) of the vertebrate liver.[71][72][73]

### Other systems

Lancelets have no respiratory system, breathing solely through their skin, which consists of a simple [epithelium](/source/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](/source/Heart). There are no blood cells, and no [hemoglobin](/source/Hemoglobin).[50]

The excretory system consists of segmented "kidneys" containing [protonephridia](/source/Nephridium) instead of [nephrons](/source/Nephron), and quite unlike those of vertebrates. Also unlike vertebrates, there are numerous, segmented [gonads](/source/Gonad).[50]

## Model organism

Lancelets became famous in the 1860s when [Ernst Haeckel](/source/Ernst_Haeckel) began promoting them as a model for the ancestor of all vertebrates. By 1900, lancelets had become a [model organism](/source/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.[74][75] More recently, the fundamental symmetric and twisted development of vertebrates is the topic of the [axial twist theory](/source/Axial_Twist_theory). According to this theory, there is a deep agreement between the vertebrates and cephalochordates, and even all chordates.[76][77]

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.[78][37]

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](/source/Gulf_of_Mexico) and West Atlantic *Branchiostoma floridae*, and the circumtropical (however, genetic evidence suggests the Atlantic and [Indo-Pacific](/source/Indo-Pacific) populations should be recognized as separate[15]) *Asymmetron lucayanum*.[68][79] They can reach an age of up to 7–8 years.[79]

## As human food

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.[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*] When their gonads start to ripen in the spring it affects their flavor, making them taste bad during their breeding season.[80]

## Phylogeny and taxonomy

The lancelet is a small, translucent, fish-like animal that is one of the closest living invertebrate relatives of the vertebrates.[81][82]

The lancelets were traditionally seen as the sister lineage to the [vertebrates](/source/Vertebrate); in turn, these two groups together (sometimes called Notochordata) were considered the sister group to the [Tunicata](/source/Tunicate) (also called Urochordata and including [sea squirts](/source/Sea_squirts)). Consistent with this view, at least ten morphological features are shared by lancelets and vertebrates, but not tunicates.[83] Newer research suggests this pattern of evolutionary relationship is incorrect. Extensive [molecular phylogenetic](/source/Molecular_phylogenetics) analysis has shown convincingly that the Cephalochordata is the most [basal](/source/Basal_(phylogenetics)) subphylum of the chordates, with tunicates being the sister group of the vertebrates.[84][85] This revised phylogeny of chordates suggests that tunicates have secondarily lost some of the morphological characters that were formerly considered to be [synapomorphies](/source/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](/source/Exon_shuffling) and domain combination.[18]

Among the three extant (living) [genera](/source/Genera), *[Asymmetron](/source/Asymmetron)* is basal. [Molecular clock](/source/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[14] while others have suggested that it occurred about [46](/source/Lutetian) million years ago.[15] According to the younger estimation, *[Branchiostoma](/source/Branchiostoma)* and *[Epigonichthys](/source/Epigonichthys)* have been estimated to have diverged from each other about [38.3](/source/Bartonian) million years ago.[15] Despite this deep separation, [hybrids](/source/Hybrid_(biology)) between *[Asymmetron lucayanum](/source/Asymmetron_lucayanum)* and *[Branchiostoma floridae](/source/Branchiostoma_floridae)* are viable (among the deepest split species known to be able to produce such hybrids).[68]

The following are the species recognised by [WoRMS](/source/World_Register_of_Marine_Species). Other sources recognize about thirty species.[75][15][86] It is likely that currently unrecognized [cryptic species](/source/Cryptic_species) remain.[68]

- **Class Leptocardii** - **Family** **Branchiostomatidae** Bonaparte 1846 - Genus *[Asymmetron](/source/Asymmetron)* Andrews 1893 [*Amphioxides* Gill 1895] - *[Asymmetron inferum](/source/Asymmetron_inferum)* Nishikawa 2004 - *[Asymmetron lucayanum](/source/Asymmetron_lucayanum)* Andrews 1893 (Sharptail lancelet) - Genus *[Branchiostoma](/source/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](/source/Branchiostoma_africae)* Hubbs 1927 - *[Branchiostoma arabiae](https://en.wikipedia.org/w/index.php?title=Branchiostoma_arabiae&action=edit&redlink=1)* Webb 1957 - *[Branchiostoma bazarutense](https://en.wikipedia.org/w/index.php?title=Branchiostoma_bazarutense&action=edit&redlink=1)* Gilchrist 1923 - *[Branchiostoma belcheri](/source/Branchiostoma_belcheri)* (Gray 1847) (Belcher's lancelet) - *[Branchiostoma bennetti](/source/Branchiostoma_bennetti)* Boschung & Gunter 1966 (Mud lancelet) - *[Branchiostoma bermudae](https://en.wikipedia.org/w/index.php?title=Branchiostoma_bermudae&action=edit&redlink=1)* Hubbs 1922 - *[Branchiostoma californiense](https://en.wikipedia.org/w/index.php?title=Branchiostoma_californiense&action=edit&redlink=1)* Andrews 1893 (Californian lancelet) - *[Branchiostoma capense](https://en.wikipedia.org/w/index.php?title=Branchiostoma_capense&action=edit&redlink=1)* Gilchrist 1902 - *[Branchiostoma caribaeum](https://en.wikipedia.org/w/index.php?title=Branchiostoma_caribaeum&action=edit&redlink=1)* Sundevall 1853 (Caribbean lancelet) - *[Branchiostoma elongatum](https://en.wikipedia.org/w/index.php?title=Branchiostoma_elongatum&action=edit&redlink=1)* (Sundevall 1852) - *[Branchiostoma floridae](/source/Branchiostoma_floridae)* Hubbs 1922 (Florida lancelet) - *[Branchiostoma gambiense](https://en.wikipedia.org/w/index.php?title=Branchiostoma_gambiense&action=edit&redlink=1)* Webb 1958 - *[Branchiostoma indicum](https://en.wikipedia.org/w/index.php?title=Branchiostoma_indicum&action=edit&redlink=1)* (Willey 1901) - *[Branchiostoma japonicum](/source/Branchiostoma_japonicum)* (Willey 1897) (Pacific lancelet) - *[Branchiostoma lanceolatum](/source/Branchiostoma_lanceolatum)* (Pallas 1774) (European lancelet) - *[Branchiostoma leonense](https://en.wikipedia.org/w/index.php?title=Branchiostoma_leonense&action=edit&redlink=1)* Webb 1956 - *[Branchiostoma longirostrum](https://en.wikipedia.org/w/index.php?title=Branchiostoma_longirostrum&action=edit&redlink=1)* Boschung 1983 (Shellhash lancelet) - *[Branchiostoma malayanum](https://en.wikipedia.org/w/index.php?title=Branchiostoma_malayanum&action=edit&redlink=1)* Webb 1956 - *[Branchiostoma moretonense](https://en.wikipedia.org/w/index.php?title=Branchiostoma_moretonense&action=edit&redlink=1)* Kelly 1966; [nomen dubium](/source/Nomen_dubium)[87][88] - *[Branchiostoma nigeriense](https://en.wikipedia.org/w/index.php?title=Branchiostoma_nigeriense&action=edit&redlink=1)* Webb 1955 - *[Branchiostoma platae](https://en.wikipedia.org/w/index.php?title=Branchiostoma_platae&action=edit&redlink=1)* Hubbs 1922 - *[Branchiostoma senegalense](https://en.wikipedia.org/w/index.php?title=Branchiostoma_senegalense&action=edit&redlink=1)* Webb 1955 - *[Branchiostoma tattersalli](https://en.wikipedia.org/w/index.php?title=Branchiostoma_tattersalli&action=edit&redlink=1)* Hubbs 1922 - *[Branchiostoma virginiae](https://en.wikipedia.org/w/index.php?title=Branchiostoma_virginiae&action=edit&redlink=1)* Hubbs 1922 (Virginian lancelet) - Genus *[Epigonichthys](/source/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](https://en.wikipedia.org/w/index.php?title=Epigonichthys_australis&action=edit&redlink=1)* (Raff 1912) - *[Epigonichthys bassanus](https://en.wikipedia.org/w/index.php?title=Epigonichthys_bassanus&action=edit&redlink=1)* (Günther 1884) - *[Epigonichthys cingalensis](https://en.wikipedia.org/w/index.php?title=Epigonichthys_cingalensis&action=edit&redlink=1)* (Kirkaldy 1894); [nomen dubium](/source/Nomen_dubium)[89] - *[Epigonichthys cultellus](https://en.wikipedia.org/w/index.php?title=Epigonichthys_cultellus&action=edit&redlink=1)* Peters 1877 - *[Epigonichthys hectori](/source/Epigonichthys_hectori)* (Benham 1901) (Hector's lancelet) - *[Epigonichthys maldivensis](https://en.wikipedia.org/w/index.php?title=Epigonichthys_maldivensis&action=edit&redlink=1)* (Foster Cooper 1903)

The [cladogram](/source/Cladistics#Cladograms) presented here illustrates the [phylogeny](/source/Phylogeny) (family tree) of lancelets, and follows a simplified version of the relationships found by Igawa and colleagues (2017):[75][15][86]

Chordata Olfactores Lancelet? †Cathaymyrus? († 518 mya) †Palaeobranchiostoma? († 273.01 mya) Lancelet (crown group) Asymmetron ⊞ ⊟ Asymmetron inferum Asymmetron lucayanum Asymmetron maldivense Epigonichthys ⊞ ⊟ Epigonichthys cultellus Epigonichthys maldivensis Branchiostoma ⊞ ⊟ Branchiostoma lanceolatum Branchiostoma floridae Branchiostoma japonicum Branchiostoma belcheri 46.0 mya 518 mya ?

## See also

- *[Phylliroe](/source/Phylliroe)*

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1. **[^](#cite_ref-YuanRuan2015_71-0)** Yuan, Shaochun; Ruan, Jie; Huang, Shengfeng; Chen, Shangwu; Xu, Anlong (February 2015). ["Amphioxus as a model for investigating evolution of the vertebrate immune system"](https://web.archive.org/web/20151222131815/http://mosas.sysu.edu.cn/lab/refsys/uppdf/201462021511673499.pdf) (PDF). *Developmental & Comparative Immunology*. **48** (2): 297–305. [doi](/source/Doi_(identifier)):[10.1016/j.dci.2014.05.004](https://doi.org/10.1016%2Fj.dci.2014.05.004). [ISSN](/source/ISSN_(identifier)) [0145-305X](https://search.worldcat.org/issn/0145-305X). [PMID](/source/PMID_(identifier)) [24877655](https://pubmed.ncbi.nlm.nih.gov/24877655). Archived from [the original](http://mosas.sysu.edu.cn/lab/refsys/uppdf/201462021511673499.pdf) (PDF) on 22 December 2015. Retrieved 16 December 2015.

1. **[^](#cite_ref-YuLecroisey2015_72-0)** Yu, Jr-Kai Sky; Lecroisey, Claire; Le Pétillon, Yann; Escriva, Hector; Lammert, Eckhard; Laudet, Vincent (2015). ["Identification, Evolution and Expression of an Insulin-Like Peptide in the Cephalochordate Branchiostoma lanceolatum"](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4361685). *PLOS ONE*. **10** (3) e0119461. [Bibcode](/source/Bibcode_(identifier)):[2015PLoSO..1019461L](https://ui.adsabs.harvard.edu/abs/2015PLoSO..1019461L). [doi](/source/Doi_(identifier)):[10.1371/journal.pone.0119461](https://doi.org/10.1371%2Fjournal.pone.0119461). [ISSN](/source/ISSN_(identifier)) [1932-6203](https://search.worldcat.org/issn/1932-6203). [PMC](/source/PMC_(identifier)) [4361685](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4361685). [PMID](/source/PMID_(identifier)) [25774519](https://pubmed.ncbi.nlm.nih.gov/25774519).

1. **[^](#cite_ref-EscrivaChao2012_73-0)** Escriva, Hector; Chao, Yeqing; Fan, Chunxin; Liang, Yujun; Gao, Bei; Zhang, Shicui (2012). ["A Novel Serpin with Antithrombin-Like Activity in Branchiostoma japonicum: Implications for the Presence of a Primitive Coagulation System"](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3299649). *PLOS ONE*. **7** (3) e32392. [Bibcode](/source/Bibcode_(identifier)):[2012PLoSO...732392C](https://ui.adsabs.harvard.edu/abs/2012PLoSO...732392C). [doi](/source/Doi_(identifier)):[10.1371/journal.pone.0032392](https://doi.org/10.1371%2Fjournal.pone.0032392). [ISSN](/source/ISSN_(identifier)) [1932-6203](https://search.worldcat.org/issn/1932-6203). [PMC](/source/PMC_(identifier)) [3299649](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3299649). [PMID](/source/PMID_(identifier)) [22427833](https://pubmed.ncbi.nlm.nih.gov/22427833).

1. **[^](#cite_ref-Hopwood2015_74-0)** Hopwood, Nick (January 2015). ["The cult of amphioxus in German Darwinism; or, Our gelatinous ancestors in Naples' blue and balmy bay"](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4286652). *History and Philosophy of the Life Sciences*. **36** (3): 371–393. [doi](/source/Doi_(identifier)):[10.1007/s40656-014-0034-x](https://doi.org/10.1007%2Fs40656-014-0034-x). [ISSN](/source/ISSN_(identifier)) [0391-9714](https://search.worldcat.org/issn/0391-9714). [PMC](/source/PMC_(identifier)) [4286652](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4286652). [PMID](/source/PMID_(identifier)) [26013195](https://pubmed.ncbi.nlm.nih.gov/26013195).

1. ^ [***a***](#cite_ref-RefTudgeVariety_75-0) [***b***](#cite_ref-RefTudgeVariety_75-1) [***c***](#cite_ref-RefTudgeVariety_75-2) [Tudge, Colin](/source/Colin_Tudge) (2000). *The Variety of Life*. Oxford University Press. [ISBN](/source/ISBN_(identifier)) [0-19-860426-2](https://en.wikipedia.org/wiki/Special:BookSources/0-19-860426-2).

1. **[^](#cite_ref-Lussanet2012_76-0)** de Lussanet, M.H.E.; Osse, J.W.M. (2012). "An ancestral axial twist explains the contralateral forebain and the optic chiasm in vertebrates". *Animal Biology*. **62** (2): 193–216. [arXiv](/source/ArXiv_(identifier)):[1003.1872](https://arxiv.org/abs/1003.1872). [doi](/source/Doi_(identifier)):[10.1163/157075611X617102](https://doi.org/10.1163%2F157075611X617102). [S2CID](/source/S2CID_(identifier)) [7399128](https://api.semanticscholar.org/CorpusID:7399128).

1. **[^](#cite_ref-Kinsbourne2013_77-0)** Kinsbourne, M. (2013). "Somatic twist: a model for the evolution of decussation". *Neuropsychology*. **27** (5): 511–515. [doi](/source/Doi_(identifier)):[10.1037/a0033662](https://doi.org/10.1037%2Fa0033662). [PMID](/source/PMID_(identifier)) [24040928](https://pubmed.ncbi.nlm.nih.gov/24040928). [S2CID](/source/S2CID_(identifier)) [11646580](https://api.semanticscholar.org/CorpusID:11646580).

1. **[^](#cite_ref-HollandLaudet2004_78-0)** Holland, L.Z.; Laudet, V.; Schubert, M. (September 2004). ["The chordate amphioxus: an emerging model organism for developmental biology"](https://www.researchgate.net/publication/8337108). *Cellular and Molecular Life Sciences*. **61** (18): 2290–2308. [doi](/source/Doi_(identifier)):[10.1007/s00018-004-4075-2](https://doi.org/10.1007%2Fs00018-004-4075-2). [ISSN](/source/ISSN_(identifier)) [1420-682X](https://search.worldcat.org/issn/1420-682X). [PMC](/source/PMC_(identifier)) [11138525](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11138525). [PMID](/source/PMID_(identifier)) [15378201](https://pubmed.ncbi.nlm.nih.gov/15378201). [S2CID](/source/S2CID_(identifier)) [28284725](https://api.semanticscholar.org/CorpusID:28284725).

1. ^ [***a***](#cite_ref-EMBRCFrance_79-0) [***b***](#cite_ref-EMBRCFrance_79-1) ["Amphioxus Branchiostoms lanceolatum"](http://www.embrc-france.fr/en/our-services/supply-biological-resources/model-organisms/amphioxus-branchiostoma-lanceolatum). EMBRC France. Retrieved 7 January 2018.[*[permanent dead link](https://en.wikipedia.org/wiki/Wikipedia:Link_rot)*]

1. **[^](#cite_ref-80)** Holland, Nicholas; Stokes, M. Dale (1998). ["The Lancelet"](https://www.researchgate.net/publication/241302129). *American Scientist*. **86** (6): 552. [Bibcode](/source/Bibcode_(identifier)):[1998AmSci..86..552S](https://ui.adsabs.harvard.edu/abs/1998AmSci..86..552S). [doi](/source/Doi_(identifier)):[10.1511/1998.6.552](https://doi.org/10.1511%2F1998.6.552).

1. **[^](#cite_ref-81)** Gewin, V (2005). ["Functional genomics thickens the biological plot"](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1149496). *PLOS Biology*. **3** (6) e219. [doi](/source/Doi_(identifier)):[10.1371/journal.pbio.0030219](https://doi.org/10.1371%2Fjournal.pbio.0030219). [PMC](/source/PMC_(identifier)) [1149496](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1149496). [PMID](/source/PMID_(identifier)) [15941356](https://pubmed.ncbi.nlm.nih.gov/15941356).

1. **[^](#cite_ref-82)** [Lancelet (amphioxus) genome and the origin of vertebrates](https://arstechnica.com/science/2008/06/lancelet-amphioxus-genome-and-the-origin-of-vertebrates/) *Ars Technica*, 19 June 2008.

1. **[^](#cite_ref-benton2005_83-0)** [Michael J. Benton](/source/Michael_J._Benton) (2005). *Vertebrate Palaeontology, Third Edition* 8. Oxford: Blackwell Publishing. [ISBN](/source/ISBN_(identifier)) [0-632-05637-1](https://en.wikipedia.org/wiki/Special:BookSources/0-632-05637-1).

1. **[^](#cite_ref-84)** Delsuc, Frédéric; Brinkmann, Henner; Chourrout, Daniel; Philippe, Hervé (2006). "Tunicates and not cephalochordates are the closest living relatives of vertebrates". *Nature*. **439** (7079): 965–8. [Bibcode](/source/Bibcode_(identifier)):[2006Natur.439..965D](https://ui.adsabs.harvard.edu/abs/2006Natur.439..965D). [doi](/source/Doi_(identifier)):[10.1038/nature04336](https://doi.org/10.1038%2Fnature04336). [OCLC](/source/OCLC_(identifier)) [784007344](https://search.worldcat.org/oclc/784007344). [PMID](/source/PMID_(identifier)) [16495997](https://pubmed.ncbi.nlm.nih.gov/16495997). [S2CID](/source/S2CID_(identifier)) [4382758](https://api.semanticscholar.org/CorpusID:4382758).

1. **[^](#cite_ref-putnam_85-0)** Putnam, N. H.; Butts, T.; Ferrier, D. E. K.; Furlong, R. F.; Hellsten, U.; Kawashima, T.; Robinson-Rechavi, M.; Shoguchi, E.; Terry, A.; Yu, J. K.; Benito-Gutiérrez, E. L.; Dubchak, I.; Garcia-Fernàndez, J.; Gibson-Brown, J. J.; Grigoriev, I. V.; Horton, A. C.; De Jong, P. J.; Jurka, J.; Kapitonov, V. V.; Kohara, Y.; Kuroki, Y.; Lindquist, E.; Lucas, S.; Osoegawa, K.; Pennacchio, L. A.; Salamov, A. A.; Satou, Y.; Sauka-Spengler, T.; Schmutz, J.; Shin-i, T. (Jun 2008). ["The amphioxus genome and the evolution of the chordate karyotype"](https://doi.org/10.1038%2Fnature06967). *Nature*. **453** (7198): 1064–1071. [Bibcode](/source/Bibcode_(identifier)):[2008Natur.453.1064P](https://ui.adsabs.harvard.edu/abs/2008Natur.453.1064P). [doi](/source/Doi_(identifier)):[10.1038/nature06967](https://doi.org/10.1038%2Fnature06967). [ISSN](/source/ISSN_(identifier)) [0028-0836](https://search.worldcat.org/issn/0028-0836). [PMID](/source/PMID_(identifier)) [18563158](https://pubmed.ncbi.nlm.nih.gov/18563158). [S2CID](/source/S2CID_(identifier)) [4418548](https://api.semanticscholar.org/CorpusID:4418548).

1. ^ [***a***](#cite_ref-:3_86-0) [***b***](#cite_ref-:3_86-1) WoRMS Editorial Board (2013). ["World Register of Marine Species- Cephalochordates species list"](http://www.marinespecies.org/aphia.php?p=taxlist&pid=1824&rComp=%3E%3D&tRank=220). Retrieved 2013-10-22.

1. **[^](#cite_ref-87)** ["UNESCO-IOC Register of Marine Organisms (URMO) - Branchiostoma mortonense Kelly, 1966"](http://www.marinespecies.org/urmo/aphia.php?p=taxdetails&id=266214).

1. **[^](#cite_ref-88)** ["WoRMS - World Register of Marine Species - Branchiostoma mortonense Kelly, 1966"](http://www.marinespecies.org/aphia.php?p=taxdetails&id=266214).

1. **[^](#cite_ref-89)** ["WoRMS - World Register of Marine Species - Epigonichthys Peters, 1876"](http://www.marinespecies.org/aphia.php?p=taxdetails&id=104903).

## Further reading

- Stach, T.G. (2004). "Cephalochordata (Lancelets)". In M. Hutchins; Garrison, R.W.; Geist, V.; Loiselle, P.V.; Schlager, N.; McDade, M.C.; Duellman, W.E. (eds.). [*Grzimek's Animal Life Encyclopedia*](/source/Grzimek's_Animal_Life_Encyclopedia). Vol. 1 (2nd ed.). Detroit, MI: Gale. pp. 485–493.

- Stokes, M.D.; Holland, N.D. (1998). "The Lancelet". *[American Scientist](/source/American_Scientist)*. **86** (6): 552–560. [doi](/source/Doi_(identifier)):[10.1511/1998.43.799](https://doi.org/10.1511%2F1998.43.799).

## External links

Wikimedia Commons has media related to [Amphioxiformes](https://commons.wikimedia.org/wiki/Category:Amphioxiformes).

[Wikispecies](/source/Wikispecies) has information related to ***[Cephalochordata](https://species.wikimedia.org/wiki/Cephalochordata)***.

- ["Cephalochordata"](http://www.ucmp.berkeley.edu/chordata/cephalo.html). [Museum of Paleontology](/source/University_of_California_Museum_of_Paleontology). Berkeley, CA: [U.C. Berkeley](/source/University_of_California%2C_Berkeley).

- ["Branchiostoma japonicum and B. belcheri are Distinct Lancelets (Cephalochordata) in Xiamen Waters in China"](https://www.researchgate.net/publication/6935781) – via [ResearchGate](/source/ResearchGate).

- ["Error in the genealogy of humans"](http://www.sars.no/research/chourroutPress.php). [Sars International Centre for Marine Molecular Biology](/source/Sars_International_Centre_for_Marine_Molecular_Biology). *sars.no* (Press release). Bergen, Norway: [University of Bergen](/source/University_of_Bergen).

- ["A special issue of Amphioxus research"](https://web.archive.org/web/20120305143024/http://www.biolsci.org/v2.php#i2). *biolsci.org*. **I**. Archived from [the original](http://www.biolsci.org/v2.php#i2) on 2012-03-05. Retrieved 2006-06-08.

- ["A special issue of Amphioxus research"](https://web.archive.org/web/20120305143024/http://www.biolsci.org/v2.php#i3). *biolsci.org*. **II**. Archived from [the original](http://www.biolsci.org/v2.php#i3) on 2012-03-05. Retrieved 2006-06-08.

- ["Amphioxus and the T-box gene"](http://news-info.wustl.edu/tips/2002/science-tech/vertebrate-invertebrate.html). *news-info.wustl.edu* (Press release). St. Louis, MO: [Washington University in St. Louis](/source/Washington_University_in_St._Louis).

- [A movie of the amphioxus embryonic development](https://www.youtube.com/watch?v=ycHJMXUT2o0) on [YouTube](/source/YouTube_video_(identifier))

- ["Scripps scientists discover fluorescence in key marine creature"](https://web.archive.org/web/20130515062324/http://scrippsnews.ucsd.edu/Releases/?releaseID=848). [Scripps Institute](/source/Scripps_Institution_of_Oceanography). *scrippsnews.ucsd.edu* (Press release). San Diego, CA: [U.C. San Diego](/source/University_of_California%2C_San_Diego). Archived from [the original](http://scrippsnews.ucsd.edu/Releases/?releaseID=848) on 2013-05-15. Retrieved 2007-11-01.

- ["Amphioxus"](https://en.wikisource.org/wiki/Encyclop%C3%A6dia_Britannica,_Ninth_Edition/Amphioxus). *[Encyclopædia Britannica](/source/Encyclop%C3%A6dia_Britannica)*. Vol. I (9th ed.). 1878. p. 774.

- ["Amphioxus: Taxonomy, brief facts, life cycle and embryology"](https://web.archive.org/web/20181010153034/http://www.geochembio.com/biology/organisms/lancelet/). *GeoChemBio*. Archived from [the original](http://www.geochembio.com/biology/organisms/lancelet/) on 2018-10-10. Retrieved 2011-03-05.

- View the [*braFlo1*](https://genome.ucsc.edu/cgi-bin/hgTracks?db=braFlo1) genome assembly in the [UCSC Genome Browser](/source/UCSC_Genome_Browser)

v t e Evolution of fish Fish Timeline of fish evolution Forerunners Basal member †Pikaia Cephalochordate †Cathaymyrus Lancelet Olfactores †Haikouella Tunicate †Myllokunmingiidae? (†Haikouichthys, †Myllokunmingia) †Zhongxiniscus? Jawless fish Cyclostomata Hagfish Hyperoartia Lamprey †Conodonts †Protoconodonta? †Paraconodontida †Conodonta †Ostracoderms †Pteraspidomorphi †Thelodonti †Anaspida †Cephalaspidomorphi †Galeaspida †Pituriaspida †Osteostraci Jawed fish †Placoderms †Antiarchi †Arthrodira †Brindabellaspida †Petalichthyida †Phyllolepida †Ptyctodontida †Rhenanida †Acanthothoraci †Pseudopetalichthyida? †Stensioellida? †Acanthodii †Acanthodiformes †"Climatiiformes" †Diplacanthiformes †Ischnacanthiformes Cartilaginous Elasmobranchii †Ctenacanthiformes †Hybodontiformes †Phoebodontiformes †Xenacanthida Ray Shark Holocephali †Eugeneodontida †Iniopterygiformes †Petalodontiformes †Symmoriiformes Chimaera Bony Lobe-finned †Onychodontiformes Coelacanth Rhipidistia †Porolepiformes Lungfish Tetrapodomorpha Ray-finned †"Palaeonisciformes" Cladistia Polypteriformes Chondrostei Acipenseriformes Neopterygii †Pycnodontiformes Halecomorphi Ginglymodi Teleost Lists Lists of prehistoric fish spiny sharks placoderms cartilaginous bony lobe-finned List of transitional fossils Related Prehistoric life Transitional fossils Vertebrate paleontology † extinct

v t e Extant animal phyla Domain Archaea Bacteria Eukaryota (major groups Metamonada Discoba Diaphoretickes Hacrobia Cryptista Rhizaria Alveolata Stramenopiles Plants Amorphea Amoebozoa Opisthokonta Animalia Fungi Mesomycetozoea) Animalia Porifera (sponges) Ctenophora (comb jellies) ParaHoxozoa (Planulozoa) Placozoa (Trichoplax and relatives) Cnidaria (jellyfish and relatives) Bilateria (Triploblasts) (see below↓) The phylogeny of the animal root is disputed; see also Eumetazoa Benthozoa Bilateria Bilateria Xenacoelomorpha (acoels and relatives) Chordata (vertebrates and relatives) Ambulacraria Echinodermata (starfish and relatives) Hemichordata (acorn worms and relatives) Protostomia Ecdysozoa Scalidophora Kinorhyncha (mud dragons) Priapulida (penis worms) Loricifera (corset animals) Cryptovermes Nematoida Nematoda (roundworms) Nematomorpha (horsehair worms) Panarthropoda Onychophora (velvet worms) Arthropoda (insects and relatives) Tardigrada (waterbears) Spiralia Gnathifera Chaetognatha (arrow worms) Gnathostomulida (jaw worms) M+R Micrognathozoa (Limnognathia) Rotifera (wheel animals inc. acanthocephalans) Platytrochozoa C+E Cycliophora (Symbion) Entoprocta or Kamptozoa Rouphozoa Platyhelminthes (flatworms) Gastrotricha (hairybacks) Mesozoa Orthonectida Dicyemida or Rhombozoa ?Monoblastozoa (Salinella) Lophotrochozoa Annelida (earth worms and relatives) Mollusca (snails and relatives) Nemertea (ribbon worms) Lophophorata Brachiopoda (lamp shells) B+P Bryozoa or Ectoprocta (moss animals) Phoronida (horseshoe worms) The phylogeny of Bilateria is disputed; see also Nephrozoa Deuterostomia Xenambulacraria Centroneuralia Major groups within phyla Sponges Demosponges Glass sponges Calcareous sponges Cnidarians Anthozoans inc. corals Medusozoans inc. jellyfish Myxozoans Chordates Lancelets Tunicates Vertebrates Echinoderms Sea lilies Asterozoans inc. starfish Echinozoans inc. sea urchins Hemichordates Acorn worms Pterobranchs Nematodes Chromadorea Enoplea Secernentea Arthropods Chelicerates inc. arachnids Myriapods Pancrustaceans inc. hexapods Rotifera Bdelloidea Monogononta Seisonidae Acanthocephala Platyhelminths Turbellaria Trematoda Monogenea Cestoda Ectoproctans Phylactolaemata Stenolaemata Gymnolaemata Annelids Polychaetes Clitellata Sipuncula Molluscs Gastropods Cephalopods Bivalves Chitons Tusk shells Phyla with ≥1000 extant species bolded Potentially dubious phyla †

v t e Extant chordate classes Kingdom Animalia Clade Bilateria Superphylum Deuterostomia Cephalochordata Leptocardii (lancelets) Olfactores Tunicata (Urochordata) Appendicularia (larvaceans) Acopa Stolidobranchia¹ Thaliacea (pyrosomes, salps, doliolids) Enterogona Phlebobranchia¹ Aplousobranchia¹ Vertebrata Cyclostomata Myxini (hagfish) Hyperoartia (lampreys) Gnathostomata (jawed vertebrates) Chondrichthyes (cartilaginous fish: sharks, rays, chimaeras) Euteleostomi (bony vertebrates) Actinopterygii (ray-finned fish) Sarcopterygii (lobe-finned fish) Actinistia (coelacanths)² Rhipidistia Dipnoi (lungfish)² Tetrapoda Lissamphibia (modern amphibians: frogs, salamanders, caecilians) Amniota Mammalia (mammals) Sauria Lepidosauria Rhynchocephalia (tuatara)³ Squamata (scaled reptiles: snakes, lizards, worm lizards)³ Archelosauria Testudines (turtles)³ Archosauria Crocodilia (crocodilians)³ Aves (birds) ¹orders of class Ascidiacea (sea squirts) ²classes of clade Sarcopterygii (lobe-finned fish and descendants) ³orders of traditional class Reptilia (reptiles) italics denote paraphyletic groups

Taxon identifiers Amphioxiformes Wikidata: Q1156226 ADW: Amphioxiformes BOLD: 343 EoL: 2773790 EPPO: 1AMPXO GBIF: 730 iNaturalist: 152875 IRMNG: 12169 ITIS: 685568 NBN: NHMSYS0020787064 NCBI: 2682553 NZOR: 4c2b8f61-5b7a-4caf-aa4b-1037907a0bb6 Leptocardii Wikidata: Q20722244 BOLD: 359990 CoL: DR EPPO: 1LEPTC GBIF: 7375758 IRMNG: 1045 NBN: NHMSYS0020787058 NCBI: 2682552 Open Tree of Life: 5665514 WoRMS: 104897 Leptocardia Wikidata: Q21286775 Wikispecies: Leptocardia ITIS: 201890 Branchiostomidae Wikidata: Q2747865 Wikispecies: Branchiostomidae ADW: Branchiostomatidae AFD: Branchiostomidae EoL: 2773791 EPPO: 1BRNSF GBIF: 2016 iNaturalist: 318011 IRMNG: 109182 ITIS: 159680 NBN: NHMSYS0000065830 Open Tree of Life: 176551 Paleobiology Database: 352170 WoRMS: 104899 Branchiostomatidae Wikidata: Q61882392 BOLD: 178131 CoL: 7NG6D GBIF: 5296 IRMNG: 106210 ITIS: 685569 NBN: NHMSYS0021053186 NCBI: 7736 Open Tree of Life: 176551 WoRMS: 196078

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Adapted from the Wikipedia article [Lancelet](https://en.wikipedia.org/wiki/Lancelet) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Lancelet?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.