Fine structure

@article{dogiel1903das,
    author = "Dogiel, A. S.",
    title = "Das Periphere Nervensystem des Amphioxus (Branchiostoma Lanceolatum)",
    year = "1903",
    journal = "Beiträge und Referate zur Anatomie und Entwickelungsgeschichte",
    url = "https://doi.org/10.1007/bf02110551",
    doi = "10.1007/bf02110551",
    number = "1",
    openalex = "W2005412999",
    pages = "145-213",
    volume = "21"
}

@article{doi101016s0022532062800070,
    author = "Eakin, Richard M. and Westfall, Jane A.",
    title = "Fine structure of photoreceptors in amphioxus",
    year = "1962",
    journal = "Journal of Ultrastructure Research",
    url = "https://doi.org/10.1016/s0022-5320(62)80007-0",
    doi = "10.1016/s0022-5320(62)80007-0",
    openalex = "W1992390853",
    references = "doi101002cne901150105, doi101007bf00320743, doi101083jcb62225, doi101083jcb82483, doi101083jcb92409, doi1010970000505319361100000044, doi101103revmodphys31301, doi10310910520296209114587, merriman1943the, smelser1943the"
}

@article{guthrie1967control,
    author = "GUTHRIE, D. M.",
    title = "Control of Muscular Contractions by Spinal Neurones in Amphioxus (Branchiostoma lanceolatum)",
    year = "1967",
    journal = "Nature",
    url = "https://doi.org/10.1038/2161224a0",
    doi = "10.1038/2161224a0",
    number = "5121",
    openalex = "W2061323334",
    pages = "1224-1225",
    volume = "216",
    references = "doi101002cne901150105, doi101002cne901260204"
}

ABSTRACT Measurements of tension and pressure from the isolated notochord during electrical stimulation indicate that the notochord of Amphioxus is a muscular organ. Muscular contraction increases the stiffness of the notochord and the pressure increase suggests that it behaves as a hydrostatic skeleton. The mechanical responses of the muscles accord fairly well with the known characteristics of other paramyosin muscles, although they are rather faster than the paramyosin muscles of most molluscs. The muscular response appears to make its greatest contribution to notochordal stiffness at the small angles of bending associated with fast swimming. Notochordal activation is preceded by a giant fibre potential. The collagen of the notochordal sheath appears to be rather more extensible than vertebrate collagen, but there is a material, probably in the elastica interna, with similar properties to elastin. The characteristics of the lancelet notochord emphasize rather than detract from the importance of its phylogenetic position.

@article{doi101242jeb521125,
    author = "Guthrie, D. M. and Banks, J. R.",
    title = "Observations on the Function and Physiological Properties of a Fast Paramyosin Muscle—The Notochord Of Amphioxus (Branchiostoma Lanceolatum)",
    year = "1970",
    journal = "Journal of Experimental Biology",
    abstract = "ABSTRACT Measurements of tension and pressure from the isolated notochord during electrical stimulation indicate that the notochord of Amphioxus is a muscular organ. Muscular contraction increases the stiffness of the notochord and the pressure increase suggests that it behaves as a hydrostatic skeleton. The mechanical responses of the muscles accord fairly well with the known characteristics of other paramyosin muscles, although they are rather faster than the paramyosin muscles of most molluscs. The muscular response appears to make its greatest contribution to notochordal stiffness at the small angles of bending associated with fast swimming. Notochordal activation is preceded by a giant fibre potential. The collagen of the notochordal sheath appears to be rather more extensible than vertebrate collagen, but there is a material, probably in the elastica interna, with similar properties to elastin. The characteristics of the lancelet notochord emphasize rather than detract from the importance of its phylogenetic position.",
    url = "https://doi.org/10.1242/jeb.52.1.125",
    doi = "10.1242/jeb.52.1.125",
    openalex = "W2263049155",
    references = "guthrie1967control"
}

Two species of primitive chordates have hyperpolarizing photoreceptor potentials, as vertebrates do. In Salpa the photoreceptive membrane is composed of microvilli, whereas in Amaroucium it is modified from cilia. There appears to be no functional correlation between fine structure of photoreceptive membrane and polarity of response to light.

@article{doi101126science17239871052,
    author = "Gorman, A. L. F. and McReynolds, John S. and Barnes, StephenN.",
    title = "Photoreceptors in Primitive Chordates: Fine Structure, Hyperpolarizing Receptor Potentials, and Evolution",
    year = "1971",
    journal = "Science",
    abstract = "Two species of primitive chordates have hyperpolarizing photoreceptor potentials, as vertebrates do. In Salpa the photoreceptive membrane is composed of microvilli, whereas in Amaroucium it is modified from cilia. There appears to be no functional correlation between fine structure of photoreceptive membrane and polarity of response to light.",
    url = "https://doi.org/10.1126/science.172.3987.1052",
    doi = "10.1126/science.172.3987.1052",
    openalex = "W2031631152",
    references = "doi101002jez1400300206, doi101007bf00331097, doi1010160042698969901345, doi101085jgp563376, doi101085jgp563392, doi101101sqb196503001036, doi101113jphysiol1959sp006270, doi101113jphysiol1970sp009049, doi101126science1653890309, doi1023071538448"
}

Analyses of high speed cinefilm have shown that amphioxus swims either forward or backward with undulatory movement generated at the leading end, the wave of displacement passing along the body with increasing amplitude. The leading end, whether this is “head” or tail, is evidently more rigid than the trailing end, flexibility at each end changing with reversal in direction of swimming. It is suggested that control of the amplitude of the waves of displacement in different regions of the body in swimming is a function of the notochord, contraction of the muscular notochordal plates increasing its stiffness. Connections between the central nervous system and the notochordal plates via the notochordal pits are already known to exist. As exposure to light invariably induces swimming in dark–adapted animals, it seems probable that the eyes function in initiating movement. The rate of increase in number and size of the eye cups during larval and adult growth and their pattern of distribution in the nerve cord are given. In the adult the eye cups occur predominantly in the anterior and posterior regions of the body. This may be of significance in providing the stimulus for changes in flexibility of these regions in swimming. High speed cinefilm has also shown that amphioxus can burrow “head” or tail‐first and move through sand in a forward or a reverse direction. It is suggested that rapid reversal of direction is of greater importance in movement through sand than in swimming.

@article{doi101111j146979981973tb01381x,
    author = "Webb, J. E.",
    title = "The role of the notochard in forward and reverse swimming and burrowing in the amphioxus Branchiostoma lanceolatum",
    year = "1973",
    journal = "Journal of Zoology",
    abstract = "Analyses of high speed cinefilm have shown that amphioxus swims either forward or backward with undulatory movement generated at the leading end, the wave of displacement passing along the body with increasing amplitude. The leading end, whether this is “head” or tail, is evidently more rigid than the trailing end, flexibility at each end changing with reversal in direction of swimming. It is suggested that control of the amplitude of the waves of displacement in different regions of the body in swimming is a function of the notochord, contraction of the muscular notochordal plates increasing its stiffness. Connections between the central nervous system and the notochordal plates via the notochordal pits are already known to exist. As exposure to light invariably induces swimming in dark–adapted animals, it seems probable that the eyes function in initiating movement. The rate of increase in number and size of the eye cups during larval and adult growth and their pattern of distribution in the nerve cord are given. In the adult the eye cups occur predominantly in the anterior and posterior regions of the body. This may be of significance in providing the stimulus for changes in flexibility of these regions in swimming. High speed cinefilm has also shown that amphioxus can burrow “head” or tail‐first and move through sand in a forward or a reverse direction. It is suggested that rapid reversal of direction is of greater importance in movement through sand than in swimming.",
    url = "https://doi.org/10.1111/j.1469-7998.1973.tb01381.x",
    doi = "10.1111/j.1469-7998.1973.tb01381.x",
    openalex = "W2001611203",
    references = "doi101002cne901150105, doi101002cne901260204, doi101007bf00335405, doi101017s0025315400033555, doi101038222087a0, doi101098rspa19520159, doi101098rstb19580007, doi101098rstb19580008, doi101242jeb521125, doi101620tjem82349, guthrie1967control"
}

Biochemical and histochemical experiments showed that the cholinesterase activity in amphioxus is due to specific acetylcholinesterase. Light and electron microscopic histochemical staining methods demonstrated that the acetylcholinesterase activity is localized to the junctions between processes of the trunk muscle fibres and the lateral surface of the spinal cord (the central motor end plate) to the junction between processes of the muscular notochordal lamellae and the ventral surface of the spinal cord (the neuro‐chordal junction) and to the junctions between the peterygal axon plexus and processes of the pterygealmuscle fibres. In the central motor end plate the dorsal and the ventral compartments, innervating superficial “red” and deep “white” trunk muscle fibres respectively, were equally intensely stained. Lower activities were seen in the spinal cord, trunk muscle. pterygeal muscle and notochord. It is concluded that most of the specific acetylcholinesterase found in amphioxus tissues is related to various kinds of neuro‐muscular junction and accordingly that these probably are cholinergic.

@article{flood1974histochemistry,
    author = "Flood, Per R.",
    title = "Histochemistry of cholinesterase in amphioxus (Branchiostoma lanceolatum, pallas)",
    year = "1974",
    journal = "Journal of Comparative Neurology",
    abstract = "Biochemical and histochemical experiments showed that the cholinesterase activity in amphioxus is due to specific acetylcholinesterase. Light and electron microscopic histochemical staining methods demonstrated that the acetylcholinesterase activity is localized to the junctions between processes of the trunk muscle fibres and the lateral surface of the spinal cord (the central motor end plate) to the junction between processes of the muscular notochordal lamellae and the ventral surface of the spinal cord (the neuro‐chordal junction) and to the junctions between the peterygal axon plexus and processes of the pterygealmuscle fibres. In the central motor end plate the dorsal and the ventral compartments, innervating superficial “red” and deep “white” trunk muscle fibres respectively, were equally intensely stained. Lower activities were seen in the spinal cord, trunk muscle. pterygeal muscle and notochord. It is concluded that most of the specific acetylcholinesterase found in amphioxus tissues is related to various kinds of neuro‐muscular junction and accordingly that these probably are cholinergic.",
    url = "https://doi.org/10.1002/cne.901570405",
    doi = "10.1002/cne.901570405",
    number = "4",
    openalex = "W1991439718",
    pages = "407-437",
    volume = "157",
    references = "doi101001jama195302940280072039, doi1010160010406x6690209x, doi101016s0096417418301069, doi101017s0025315400027168, doi101042bj1150465, doi101083jcb171208, doi101177123219, doi103181003797277017013, guthrie1967control, openalexw1444750168, openalexw2985956097"
}

@inproceedings{southward1975fine1,
    author = "Southward, E. C",
    title = "Fine structure and phylogeny of the Pogonomorpha",
    year = "1975",
    booktitle = "Symposium of the Zoological Society, London, v. 36, p. 235-251",
    note = "talkorigins\_source = {true}; raw\_reference = {Southward, E. C., 1975, Fine structure and phylogeny of the Pogonomorpha: Symposium of the Zoological Society, London, v. 36, p. 235-251.}"
}

@inproceedings{welsch1975the2,
    author = "Welsch, U",
    title = "The fine structure of the pharynx, cryptopodocytes and digestive system of amphioxus (Branchiostoma lanceolatum)",
    year = "1975",
    booktitle = "Symposium of the Zoological Society, London, v. 36, p. 17-41",
    note = "talkorigins\_source = {true}; raw\_reference = {Welsch, U., 1975, The fine structure of the pharynx, cryptopodocytes and digestive system of amphioxus (Branchiostoma lanceolatum): Symposium of the Zoological Society, London, v. 36, p. 17-41.}"
}

@article{rähr1979the,
    author = "Rähr, H.",
    title = "The Circulatory System of Amphioxus (Branchiostoma lanceolatum (Pallas))",
    year = "1979",
    journal = "Acta Zoologica",
    url = "https://doi.org/10.1111/j.1463-6395.1979.tb00594.x",
    doi = "10.1111/j.1463-6395.1979.tb00594.x",
    number = "1",
    openalex = "W1990682207",
    pages = "1-18",
    volume = "60",
    references = "doi101002jmor1051390403, doi1010079783642651045, doi10100797836429105483, doi101007bf02933895, doi101016s0022532071900207, doi1023073225209, doi105962bhltitle159385, doi105962bhltitle6408, moller1973the, openalexw2321178397"
}

Corpuscles of de Quatrefages in the rostral connective tissue of amphioxus have been serially sectioned and examined in the electron microscope. It is shown that each corpuscle is composed of one or a few main cells separated and enveloped by sheath cells. From the main cell two cilia protrude into a lumen formed by a bulge in the sheath. The ciliation of the main cell and its axonic continuation into one of the associated nerves suggests that this cell is a primary sensory neurone and the corpuscles of de Quatrefages probably mechanoreceptors.

@article{doi101111j146363951982tb00757x,
    author = "Baatrup, Erik",
    title = "On the Structure of the Corpuscles of de Quatrefages (Branchiostoma lanceolatum (P))",
    year = "1982",
    journal = "Acta Zoologica",
    abstract = "Corpuscles of de Quatrefages in the rostral connective tissue of amphioxus have been serially sectioned and examined in the electron microscope. It is shown that each corpuscle is composed of one or a few main cells separated and enveloped by sheath cells. From the main cell two cilia protrude into a lumen formed by a bulge in the sheath. The ciliation of the main cell and its axonic continuation into one of the associated nerves suggests that this cell is a primary sensory neurone and the corpuscles of de Quatrefages probably mechanoreceptors.",
    url = "https://doi.org/10.1111/j.1463-6395.1982.tb00757.x",
    doi = "10.1111/j.1463-6395.1982.tb00757.x",
    openalex = "W2007096492",
    references = "dogiel1903das"
}

Abstract The fine structure of the chorion and the region of the unfertilized egg immediately beneath the micropylar apparatus of the zebra danio, Brachydanio rerio, were studied using Nomarski differential interference optics, and scanning and transmission electron microscopy. The chorion consisted of three distinct zones: an outer, electron‐dense zone containing pore canal plugs (zona radiata externa), a middle fibrillar zone (superficial zona radiata interna), and an inner zone of 16 horizontal electrondense lamellae alternating with 15 interlamellae of lower electron density (deep zona radiata interna). The zona radiata interna was pierced by open pore canals. The single micropylar apparatus was regionalized into a cone‐shaped vestibule and a tapered micropylar canal traversing the entire chorion. The outer diameter of the micropylar canal was 7.5–8.5 μn and the inner diameter about 2.3 μn. Since the diameter of the inner micropylar aperture was slightly larger than the size of the sperm head, the block to polyspermy in eggs of the zebra danio appears to be mechanical and guaranteed by the morphological design of the micropyle. The egg plasmalemma beneath the inner micropylar aperture was differentiated as a circular cluster of 15–20 microvilli‐like projections. The cluster of surface projections, approximately 2.1–2.5 μn in diameter under scanning, electron microscopy, was distinguishable from the microplicae covering the rest of the egg surface and identified as the sperm entry site. The cortical cytoplasm subjacent to the sperm entry site was organized as a compact, electron‐dense, and homogeneous band. The sperm entry site itself was circumscribed by an area of cytoplasm (approximately 100 μn in diameter) in which cortical granules were typically arranged as a single layer immediately beneath the plasmalemma. However, there was a complete absence of cortical granules in the cytoplasm directly below the sperm entry site. The single row arrangement contrasted with the multilayered rows of cortical granules found throughout the remainder of the egg cytoplasm. Based upon Nomarski and ultrastructural analyses, there was a significant polarity in the cortex created by the size distribution and volume density of the cortical granules layered just beneath the plasmalemma. The cortical granules in the vicinity of the sperm entry site were 2.7 to 2.8 μm in diameter and densely packed. From this region to the vegetal pole, the cortical granules appeared to progressively increase in size and become less densely packed. The polarity in granule distribution established a distinct gradient in the structural organization of the egg cortex from the site of sperm entry to the vegetal pole.

@article{doi101002jez1402270212,
    author = "Hart, Nathan H. and Donovan, Michael J.",
    title = "Fine structure of the chorion and site of sperm entry in the egg of Brachydanio",
    year = "1983",
    journal = "Journal of Experimental Zoology",
    abstract = "Abstract The fine structure of the chorion and the region of the unfertilized egg immediately beneath the micropylar apparatus of the zebra danio, Brachydanio rerio, were studied using Nomarski differential interference optics, and scanning and transmission electron microscopy. The chorion consisted of three distinct zones: an outer, electron‐dense zone containing pore canal plugs (zona radiata externa), a middle fibrillar zone (superficial zona radiata interna), and an inner zone of 16 horizontal electrondense lamellae alternating with 15 interlamellae of lower electron density (deep zona radiata interna). The zona radiata interna was pierced by open pore canals. The single micropylar apparatus was regionalized into a cone‐shaped vestibule and a tapered micropylar canal traversing the entire chorion. The outer diameter of the micropylar canal was 7.5–8.5 μn and the inner diameter about 2.3 μn. Since the diameter of the inner micropylar aperture was slightly larger than the size of the sperm head, the block to polyspermy in eggs of the zebra danio appears to be mechanical and guaranteed by the morphological design of the micropyle. The egg plasmalemma beneath the inner micropylar aperture was differentiated as a circular cluster of 15–20 microvilli‐like projections. The cluster of surface projections, approximately 2.1–2.5 μn in diameter under scanning, electron microscopy, was distinguishable from the microplicae covering the rest of the egg surface and identified as the sperm entry site. The cortical cytoplasm subjacent to the sperm entry site was organized as a compact, electron‐dense, and homogeneous band. The sperm entry site itself was circumscribed by an area of cytoplasm (approximately 100 μn in diameter) in which cortical granules were typically arranged as a single layer immediately beneath the plasmalemma. However, there was a complete absence of cortical granules in the cytoplasm directly below the sperm entry site. The single row arrangement contrasted with the multilayered rows of cortical granules found throughout the remainder of the egg cytoplasm. Based upon Nomarski and ultrastructural analyses, there was a significant polarity in the cortex created by the size distribution and volume density of the cortical granules layered just beneath the plasmalemma. The cortical granules in the vicinity of the sperm entry site were 2.7 to 2.8 μm in diameter and densely packed. From this region to the vegetal pole, the cortical granules appeared to progressively increase in size and become less densely packed. The polarity in granule distribution established a distinct gradient in the structural organization of the egg cortex from the site of sperm entry to the vegetal pole.",
    url = "https://doi.org/10.1002/jez.1402270212",
    doi = "10.1002/jez.1402270212",
    openalex = "W1980922705"
}

The ovary of Stichopus californicus consists of several size classes of tubules, which insert into a central gonad basis. The largest tubules contain the oocytes that will be spawned in the current season. All tubules are composed of three layers. Outermost is a complex peritoneum composed of epithelial cells, axons and muscle cells. The fine structure of the peritoneal neurons suggests their involvement in neurosecretory activity. Between the basal laminae of the peritoneum and the inner epithelium is the ovarian connective tissue compartment, including the genital hemal sinus. This sinus probably conveys nutrients from the periphery of the tubule to oocytes located deep within. The inner epithelium is composed of parietal and follicular epithelial cells and the oocytes. Stichopus oocytes contain three classes of microtubules based upon their location, orientation, and lability during fixation. Microtubules from the apical protuberance encircle the germinal vesicle. Cortical microtubules lie just under the cell surface and run parallel to it. Deep cytoplasmic microtubules run radially from the interior of the oocyte towards the cell surface. Oocytes are held within follicles by junctional complexes until the time of ovulation. Ovulation can be monitored in severed follicles of this species because an oolamina insures follicle integrity after detachment from the ovary. The onset of ovulation is marked by the dissolution of junctional complexes. This is followed by a cytochalasin B sensitive contraction of the follicle cells. The follicle contracts down around the oocyte, to lie collapsed against the ovarian wall while the oocyte is free within the ovarian lumen.

@article{doi1023071541487,
    author = "Smiley, Scott and Cloney, RichardA.",
    title = "OVULATION AND THE FINE STRUCTURE OF THE STICHOPUS CALIFORNICUS (ECHINODERMATA: HOLOTHUROIDEA) FECUND OVARIAN TUBULES",
    year = "1985",
    journal = "Biological Bulletin",
    abstract = "The ovary of Stichopus californicus consists of several size classes of tubules, which insert into a central gonad basis. The largest tubules contain the oocytes that will be spawned in the current season. All tubules are composed of three layers. Outermost is a complex peritoneum composed of epithelial cells, axons and muscle cells. The fine structure of the peritoneal neurons suggests their involvement in neurosecretory activity. Between the basal laminae of the peritoneum and the inner epithelium is the ovarian connective tissue compartment, including the genital hemal sinus. This sinus probably conveys nutrients from the periphery of the tubule to oocytes located deep within. The inner epithelium is composed of parietal and follicular epithelial cells and the oocytes. Stichopus oocytes contain three classes of microtubules based upon their location, orientation, and lability during fixation. Microtubules from the apical protuberance encircle the germinal vesicle. Cortical microtubules lie just under the cell surface and run parallel to it. Deep cytoplasmic microtubules run radially from the interior of the oocyte towards the cell surface. Oocytes are held within follicles by junctional complexes until the time of ovulation. Ovulation can be monitored in severed follicles of this species because an oolamina insures follicle integrity after detachment from the ovary. The onset of ovulation is marked by the dissolution of junctional complexes. This is followed by a cytochalasin B sensitive contraction of the follicle cells. The follicle contracts down around the oocyte, to lie collapsed against the ovarian wall while the oocyte is free within the ovarian lumen.",
    url = "https://doi.org/10.2307/1541487",
    doi = "10.2307/1541487",
    openalex = "W2125682142",
    references = "doi101007bf00217887, doi101007bf00310477, doi101007bf00347297, doi101007bf00994084, doi1010160014482771906422, doi101083jcb902362, doi101111j146363951981tb00618x, doi101126science1713967135, doi1023071540860, openalexw2769238570"
}

@article{holland1991the,
    author = "HOLLAND, NICHOLAS D. and HOLLAND, LINDA Z.",
    title = "The fine structure of the growth stage oocytes of a lancelet (= amphioxus), Branchiostoma lanceolatum",
    year = "1991",
    journal = "Invertebrate Reproduction \& Development",
    url = "https://doi.org/10.1080/07924259.1991.9672164",
    doi = "10.1080/07924259.1991.9672164",
    number = "2",
    openalex = "W1978865276",
    pages = "107-122",
    volume = "19",
    references = "doi101002jmor1050540103, doi101002jmor1052020304, doi101007bf00409571, doi1010160012160687903320, doi101016030744127990092x, doi101083jcb78158, doi1023071541487, doi1023071541575, doi105281zenodo16497931, openalexw574596740"
}

@article{ruiz1991the,
    author = "Ruiz, Soledad and Anad�n, Ram�n",
    title = "The fine structure of lamellate cells in the brain of amphioxus (Branchiostoma lanceolatum, Cephalochordata)",
    year = "1991",
    journal = "Cell and Tissue Research",
    url = "https://doi.org/10.1007/bf00327295",
    doi = "10.1007/bf00327295",
    number = "3",
    openalex = "W1574791065",
    pages = "597-600",
    volume = "263",
    references = "doi101007978146130515615, doi101007bf00339290, doi101007bf00348527, doi101007bf02028391, doi101007bf02584045, doi1010160002939482901581, doi101016s0022532062800070, doi101085jgp563376, doi101126science17239871052, openalexw2394638245"
}

To obtain information about the evolution of the cholinesterases, acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) in the vertebrates, we investigated the cholinesterase (ChE) activity of the cephalochordate amphioxus (Branchiostoma floridae and Branchiostoma lanceolatum). On the basis of evidence from enzymology, pharmacology, and molecular biology, we conclude that amphioxus possesses two ChE activities and two ChE genes. Two covalent inhibitors of cholinesterases were able to pharmacologically isolate the two activities as drug-sensitive ChE and drug-resistant ChE. Kinetically, in terms of substrate specificity, the drug-sensitive ChE resembles vertebrate AChE, and the drug-resistant ChE resembles the BuChE of cartilaginous and bony fish or the intermediate ChE of protostome invertebrates. We also used the polymerase chain reaction with degenerate oligonucleotide primers and genomic DNA to obtain clones of 1,574 and 1,011 bp corresponding to two cholinesterase genes from amphioxus, which we designated as ChE1 and ChE2. ChE2 codes for an enzyme with an acyl-binding pocket sequence, a portion of the protein that plays an important role in determining substrate specificity, typical of invertebrate ChE. ChE1, which contains a 503-bp intron, encodes a protein with a novel acyl binding site. Phylogenetic analysis of the sequences suggests that the two genes are a result of a duplication event in the lineage leading to amphioxus. We discuss the relevance of our results to the evolution of the cholinesterases in the chordates. Previously, we reported that amphioxus contained a single cholinesterase activity with properties intermediate to AChE and BuChE (Pezzementi et al. [1991] In: Cholinesterases: Structure, Function, Mechanism, Genetics and Cell Biology. J. Massoulié et al., eds. ACS: Washington, D.C., pp. 24-31).

@article{doi101002sici1097010x199702152773213aidjez330co2r,
    author = "Sutherland, David J. and McClellan, James Scott and Milner, Daniel A. and Soong, Weily and Axon, Neal and Sanders, Michael and Hester, Alison and Kao, Yu-Hsing and Poczatek, Ted and Routt, Sheri M. and Pezzementi, Leo",
    title = "Two cholinesterase activities and genes are present in amphioxus",
    year = "1997",
    journal = "Journal of Experimental Zoology",
    abstract = "To obtain information about the evolution of the cholinesterases, acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) in the vertebrates, we investigated the cholinesterase (ChE) activity of the cephalochordate amphioxus (Branchiostoma floridae and Branchiostoma lanceolatum). On the basis of evidence from enzymology, pharmacology, and molecular biology, we conclude that amphioxus possesses two ChE activities and two ChE genes. Two covalent inhibitors of cholinesterases were able to pharmacologically isolate the two activities as drug-sensitive ChE and drug-resistant ChE. Kinetically, in terms of substrate specificity, the drug-sensitive ChE resembles vertebrate AChE, and the drug-resistant ChE resembles the BuChE of cartilaginous and bony fish or the intermediate ChE of protostome invertebrates. We also used the polymerase chain reaction with degenerate oligonucleotide primers and genomic DNA to obtain clones of 1,574 and 1,011 bp corresponding to two cholinesterase genes from amphioxus, which we designated as ChE1 and ChE2. ChE2 codes for an enzyme with an acyl-binding pocket sequence, a portion of the protein that plays an important role in determining substrate specificity, typical of invertebrate ChE. ChE1, which contains a 503-bp intron, encodes a protein with a novel acyl binding site. Phylogenetic analysis of the sequences suggests that the two genes are a result of a duplication event in the lineage leading to amphioxus. We discuss the relevance of our results to the evolution of the cholinesterases in the chordates. Previously, we reported that amphioxus contained a single cholinesterase activity with properties intermediate to AChE and BuChE (Pezzementi et al. [1991] In: Cholinesterases: Structure, Function, Mechanism, Genetics and Cell Biology. J. Massoulié et al., eds. ACS: Washington, D.C., pp. 24-31).",
    url = "https://doi.org/10.1002/(sici)1097-010x(19970215)277:3<213::aid-jez3>3.0.co;2-r",
    doi = "10.1002/(sici)1097-010x(19970215)277:3<213::aid-jez3>3.0.co;2-r",
    openalex = "W2039931272",
    references = "flood1974histochemistry"
}

@article{fagotti1998actin,
    author = "Fagotti, Anna and Di Rosa, Ines and Simoncelli, Francesca and Chaponnier, Christine and Gabbiani, Giulio and Pascolini, R.",
    title = "Actin isoforms in amphioxus Branchiostoma lanceolatum",
    year = "1998",
    journal = "Cell and Tissue Research",
    url = "https://doi.org/10.1007/s004410051047",
    doi = "10.1007/s004410051047",
    number = "1",
    openalex = "W2050707594",
    pages = "173-176",
    volume = "292"
}

@article{riisgard1999filter,
    author = "Riisgard, Hans Ulrik and Svane, Ib",
    title = "Filter Feeding in Lancelets (Amphioxus), Branchiostoma lanceolatum",
    year = "1999",
    journal = "Invertebrate Biology",
    url = "https://doi.org/10.2307/3227011",
    doi = "10.2307/3227011",
    number = "4",
    openalex = "W2335253372",
    pages = "423",
    volume = "118",
    references = "doi101007bf00386593, doi1010160300962989905598, doi101111j1469185x1995tb01440x, doi101139z90111, doi1023071308815, doi103354meps001055, doi103354meps015283, doi103354meps141037, doi105860choice501469, orton1913the"
}

The anatomical diffusing factors (ADFs), defined as the ratio of surface area to the thickness of the diffusion barrier, of possible respiratory surfaces of adult amphioxus (Branchiostoma lanceolatum) were evaluated using stereological methods. The ADF is greatest for the lining of the atrium and for the skin covering the segmental muscles. Calculation of the diffusing capacities for O(2) revealed that the lining of the atrium makes up nearly 83 % of the entire diffusing capacity (8.86 x 10(-3) microl min(-1)mg(-1)kPa(-1) while the skin over the segmental muscles (9%), the skin over the metapleural fold (4%) and the gill bars (4%) are of minor importance. The diffusing capacity of surfaces lying over coelomic cavities makes up 76% of the whole diffusing capacity, which is consistent with the hypothesis that the coelom may function as a circulatory system for respiratory gases. Muscles have approximately 23% of the entire diffusing capacity, indicating that they may be self-sufficient for O(2) uptake. The diffusing capacity of the blood vessels in the gill bars is only 1% of the total. Thus, the 'gills' lack significant function as respiratory organs in amphioxus (lancelets).

@article{doi101242jeb203223381,
    author = "Schmitz, Anke and Gemmel, Maj and Perry, Steven F.",
    title = "Morphometric Partitioning of Respiratory Surfaces in Amphioxus (Branchiostoma Lanceolatum Pallas)",
    year = "2000",
    journal = "Journal of Experimental Biology",
    abstract = "The anatomical diffusing factors (ADFs), defined as the ratio of surface area to the thickness of the diffusion barrier, of possible respiratory surfaces of adult amphioxus (Branchiostoma lanceolatum) were evaluated using stereological methods. The ADF is greatest for the lining of the atrium and for the skin covering the segmental muscles. Calculation of the diffusing capacities for O(2) revealed that the lining of the atrium makes up nearly 83 \% of the entire diffusing capacity (8.86 x 10(-3) microl min(-1)mg(-1)kPa(-1) while the skin over the segmental muscles (9\%), the skin over the metapleural fold (4\%) and the gill bars (4\%) are of minor importance. The diffusing capacity of surfaces lying over coelomic cavities makes up 76\% of the whole diffusing capacity, which is consistent with the hypothesis that the coelom may function as a circulatory system for respiratory gases. Muscles have approximately 23\% of the entire diffusing capacity, indicating that they may be self-sufficient for O(2) uptake. The diffusing capacity of the blood vessels in the gill bars is only 1\% of the total. Thus, the 'gills' lack significant function as respiratory organs in amphioxus (lancelets).",
    url = "https://doi.org/10.1242/jeb.203.22.3381",
    doi = "10.1242/jeb.203.22.3381",
    openalex = "W2186186445",
    references = "doi101111j146363951990tb01081x, riisgard1999filter"
}

Abstract In a classic study with silver staining methods, the somatomotor system of the amphioxus spinal cord was described as consisting of three different types of neuron segmentally arranged in two opposite fan‐shaped group types (Bone [1960] J Comp Neurol 115:27–64). The present study reports the presence of calretinin‐like immunoreactivity in the somatomotor system of the amphioxus, which allows us to reevaluate old descriptions of amphioxus motoneurons. In the spinal cord, two types of calretinin‐like immunoreactive (CR‐ir) motoneurons, large and small, sent processes toward the ventrolateral region of the cord, where they branched and gave rise to processes coursing longitudinally in the somatomotor bundles. These processes produced a number of long and thin collaterals directed to several neuropil regions. Short collaterals were directed to the region of the neuromuscular contacts at the ventrolateral surface of the cord. The groups of CR‐ir motoneurons exhibited a segmental organization and were localized only facing the myomeres, i.e., opposite to the entrance of the dorsal nerve roots, which is at variance with the above‐mentioned classical report. CR‐ir motoneurons were also observed in the brain between a level just rostral to the nerve III entry and nerve VI. The CR‐ir somatomotor bundle ascended to the region of the neuromuscular junction of myomere 1. Additional faintly CR‐ir neurons were observed in the region of the lamellate body of the brain. Our results reveal for the first time that calretinin immunoreactivity in the central nervous system of amphioxus was limited to a few types of neuron and that calretinin was not expressed in the peripheral nervous system, unlike vertebrates. J. Comp. Neurol. 477:161–171, 2004. © 2004 Wiley‐Liss, Inc.

@article{doi101002cne20243,
    author = "Castro, A. and Becerra, Manuela and Manso, Marı́a Jesús and Anadón, Ramón",
    title = "Somatomotor system of the adult amphioxus (Branchiostoma lanceolatum) revealed by an anticalretinin antiserum: An immunocytochemical study",
    year = "2004",
    journal = "The Journal of Comparative Neurology",
    abstract = "Abstract In a classic study with silver staining methods, the somatomotor system of the amphioxus spinal cord was described as consisting of three different types of neuron segmentally arranged in two opposite fan‐shaped group types (Bone [1960] J Comp Neurol 115:27–64). The present study reports the presence of calretinin‐like immunoreactivity in the somatomotor system of the amphioxus, which allows us to reevaluate old descriptions of amphioxus motoneurons. In the spinal cord, two types of calretinin‐like immunoreactive (CR‐ir) motoneurons, large and small, sent processes toward the ventrolateral region of the cord, where they branched and gave rise to processes coursing longitudinally in the somatomotor bundles. These processes produced a number of long and thin collaterals directed to several neuropil regions. Short collaterals were directed to the region of the neuromuscular contacts at the ventrolateral surface of the cord. The groups of CR‐ir motoneurons exhibited a segmental organization and were localized only facing the myomeres, i.e., opposite to the entrance of the dorsal nerve roots, which is at variance with the above‐mentioned classical report. CR‐ir motoneurons were also observed in the brain between a level just rostral to the nerve III entry and nerve VI. The CR‐ir somatomotor bundle ascended to the region of the neuromuscular junction of myomere 1. Additional faintly CR‐ir neurons were observed in the region of the lamellate body of the brain. Our results reveal for the first time that calretinin immunoreactivity in the central nervous system of amphioxus was limited to a few types of neuron and that calretinin was not expressed in the peripheral nervous system, unlike vertebrates. J. Comp. Neurol. 477:161–171, 2004. © 2004 Wiley‐Liss, Inc.",
    url = "https://doi.org/10.1002/cne.20243",
    doi = "10.1002/cne.20243",
    openalex = "W1983564788",
    references = "flood1974histochemistry"
}

We show in this paper that amphioxus (Branchiostoma lanceolatum) is capable of collecting sub-micron particles on its mucous filter. This is made by an endostyle in some respects simpler than those of tunicates, and that unlike the filters in tunicates, the strands of the amphioxus filter are sticky. It therefore does not act simply as a sieve.

@article{nielsen2007on,
    author = "Nielsen, S.E. and Bone, Q. and Bond, P. and Harper, G.",
    title = "On particle filtration by amphioxus (Branchiostoma lanceolatum)",
    year = "2007",
    journal = "Journal of the Marine Biological Association of the United Kingdom",
    abstract = "We show in this paper that amphioxus (Branchiostoma lanceolatum) is capable of collecting sub-micron particles on its mucous filter. This is made by an endostyle in some respects simpler than those of tunicates, and that unlike the filters in tunicates, the strands of the amphioxus filter are sticky. It therefore does not act simply as a sieve.",
    url = "https://doi.org/10.1017/s0025315407053519",
    doi = "10.1017/s0025315407053519",
    number = "4",
    openalex = "W2010106646",
    pages = "983-989",
    volume = "87"
}

The amphioxus is often used as a model marine animal in biological research because of its special position in evolution. These animals have transparent surfaces and nonrespiratory gills, and whether such specialization plays a role in the accumulation of metals remains unknown. In the present study, we determined the biokinetics of Cd and Zn in the amphioxus Branchiostoma belcheri, including metal assimilation efficiency (AE), the dissolved Cd and Zn uptake rate constants, and the efflux rate constant. Metal AEs were 7.6 to 34.3% for Cd and 8.4 to 42.9% for Zn in amphioxus feeding on 5 different algae, and the AEs of Zn were significantly influenced by the algal con centration. The dissolved uptake rate constants were 0.107 l g -1 d -1 for Cd and 0.061 l g -1 d -1 for Zn. The efflux rate constants were 0.012 to 0.033 d -1 for Cd and 0.031 to 0.040 d -1 for Zn following dietary or waterborne metal exposure. Overall, these determined bio kinetics were comparable to those found in other suspension feeders, such as marine bivalves. However, amphioxus had a higher absorption efficiency from the dissolved phase than those found for marine bivalves, largely caused by the unique surface sorption of metals. Such unique surface uptake contributed to the dominance of waterborne Cd accumulation in amphioxus under most environmental conditions. For Zn, dietary exposure appeared to be more important than aqueous uptake due to its relatively high particle reactivity. The predicted trophic transfer factors of Cd and Zn were <1 under most conditions.

@article{doi103354ab00447,
    author = "Lü, Bin and Ke, Caihuan and Wang, Wen‐Xiong",
    title = "Importance of waterborne cadmium and zinc accumulation in the suspension-feeding amphioxus Branchiostoma belcheri",
    year = "2012",
    journal = "Aquatic Biology",
    abstract = "The amphioxus is often used as a model marine animal in biological research because of its special position in evolution. These animals have transparent surfaces and nonrespiratory gills, and whether such specialization plays a role in the accumulation of metals remains unknown. In the present study, we determined the biokinetics of Cd and Zn in the amphioxus Branchiostoma belcheri, including metal assimilation efficiency (AE), the dissolved Cd and Zn uptake rate constants, and the efflux rate constant. Metal AEs were 7.6 to 34.3\% for Cd and 8.4 to 42.9\% for Zn in amphioxus feeding on 5 different algae, and the AEs of Zn were significantly influenced by the algal con centration. The dissolved uptake rate constants were 0.107 l g -1 d -1 for Cd and 0.061 l g -1 d -1 for Zn. The efflux rate constants were 0.012 to 0.033 d -1 for Cd and 0.031 to 0.040 d -1 for Zn following dietary or waterborne metal exposure. Overall, these determined bio kinetics were comparable to those found in other suspension feeders, such as marine bivalves. However, amphioxus had a higher absorption efficiency from the dissolved phase than those found for marine bivalves, largely caused by the unique surface sorption of metals. Such unique surface uptake contributed to the dominance of waterborne Cd accumulation in amphioxus under most environmental conditions. For Zn, dietary exposure appeared to be more important than aqueous uptake due to its relatively high particle reactivity. The predicted trophic transfer factors of Cd and Zn were <1 under most conditions.",
    url = "https://doi.org/10.3354/ab00447",
    doi = "10.3354/ab00447",
    openalex = "W2331134327",
    references = "nielsen2007on"
}

Amphioxus (Cephalochordata) belongs to the most basal extant chordates, and knowledge of their brain organization appears to be key to deciphering the early stages of evolution of vertebrate brains. Most comprehensive studies of the organization of the central nervous system of adult amphioxus have investigated the spinal cord. Some brain populations have been characterized via neurochemistry and electron microscopy, and the overall cytoarchitecture of the brain was studied by Ekhart et al. (2003; J. Comp. Neurol. 466:319-330) with general staining methods and retrograde transport from the spinal cord. Here, the cytoarchitecture of the brain of adult amphioxus Branchiostoma lanceolatum was reinvestigated by using acetylated tubulin immunohistochemistry, which specifically stains neurons and fibers, in combination with some ancillary methods. This method allowed reproducible staining and mapping of types of neuron, mostly in brain regions caudal to the entrance level of nerve 2, and its comparison with spinal cord populations. The brain populations studied and discussed in detail were the Retzius bipolar cells, lamellate cells, Joseph cells, various types of translumenal cells, somatic motoneurons, Rohde nucleus cells, small ventral multipolar neurons, and Edinger cells. These observations expand our knowledge of the distribution of cell types and provide additional data on the number of cells and the axonal tracts and commissural regions of the adult amphioxus brain. The results of this comprehensive study provide a framework for comparison of complex adult populations with the early brain neuronal populations revealed in developmental studies of the amphioxus.

@article{doi101002cne23785,
    author = "Castro, A. and Becerra, Manuela and Manso, Marı́a Jesús and Anadón, Ramón",
    title = "Neuronal organization of the brain in the adult amphioxus (Branchiostoma lanceolatum): A study with acetylated tubulin immunohistochemistry",
    year = "2015",
    journal = "The Journal of Comparative Neurology",
    abstract = "Amphioxus (Cephalochordata) belongs to the most basal extant chordates, and knowledge of their brain organization appears to be key to deciphering the early stages of evolution of vertebrate brains. Most comprehensive studies of the organization of the central nervous system of adult amphioxus have investigated the spinal cord. Some brain populations have been characterized via neurochemistry and electron microscopy, and the overall cytoarchitecture of the brain was studied by Ekhart et al. (2003; J. Comp. Neurol. 466:319-330) with general staining methods and retrograde transport from the spinal cord. Here, the cytoarchitecture of the brain of adult amphioxus Branchiostoma lanceolatum was reinvestigated by using acetylated tubulin immunohistochemistry, which specifically stains neurons and fibers, in combination with some ancillary methods. This method allowed reproducible staining and mapping of types of neuron, mostly in brain regions caudal to the entrance level of nerve 2, and its comparison with spinal cord populations. The brain populations studied and discussed in detail were the Retzius bipolar cells, lamellate cells, Joseph cells, various types of translumenal cells, somatic motoneurons, Rohde nucleus cells, small ventral multipolar neurons, and Edinger cells. These observations expand our knowledge of the distribution of cell types and provide additional data on the number of cells and the axonal tracts and commissural regions of the adult amphioxus brain. The results of this comprehensive study provide a framework for comparison of complex adult populations with the early brain neuronal populations revealed in developmental studies of the amphioxus.",
    url = "https://doi.org/10.1002/cne.23785",
    doi = "10.1002/cne.23785",
    openalex = "W1882862961",
    references = "castro2003distribution, doi101007bf00348527, doi101007bf02028391, doi101007bf02933895, doi101387ijdb072436jg, holmes1953the, openalexw2394638245"
}

We present a genome assembly from a specimen of Branchiostoma lanceolatum (Amphioxus; Chordata; Leptocardii; Amphioxiformes; Branchiostomatidae). The assembly contains two haplotypes with total lengths of 468.40 megabases and 465.81 megabases, respectively. Most of haplotype 1 (99.34%) is scaffolded into 19 chromosomal pseudomolecules. Haplotype 2 is a scaffold level assembly. The mitochondrial genome has also been assembled and is 15.14 kilobases in length.

@article{adkins2025the,
    author = "Adkins, Patrick and Bishop, John and Harley, Joanna and Holland, Peter W. H.",
    title = "The genome sequence of the amphioxus, Branchiostoma lanceolatum (Pallas, 1774)",
    year = "2025",
    journal = "Wellcome Open Research",
    abstract = "We present a genome assembly from a specimen of Branchiostoma lanceolatum (Amphioxus; Chordata; Leptocardii; Amphioxiformes; Branchiostomatidae). The assembly contains two haplotypes with total lengths of 468.40 megabases and 465.81 megabases, respectively. Most of haplotype 1 (99.34\%) is scaffolded into 19 chromosomal pseudomolecules. Haplotype 2 is a scaffold level assembly. The mitochondrial genome has also been assembled and is 15.14 kilobases in length.",
    url = "https://doi.org/10.12688/wellcomeopenres.23671.1",
    doi = "10.12688/wellcomeopenres.23671.1",
    openalex = "W4407906736",
    pages = "95",
    volume = "10",
    references = "doi101016jcell201411021, doi101016s0022283605803602, doi101038nbt3820, doi101038s41592020010565, doi101038s4159202101101x, doi101093bioinformaticsbtq033, doi101093bioinformaticsbtw354, doi101093bioinformaticsbty191, doi101093gigasciencegiab008, doi101093nargkac1052"
}