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Branchial arches, or gill arches, are a series of bony "loops" present in fish, which support the
gills A gill () is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic ...
. As gills are the primitive condition of vertebrates, all vertebrate embryos develop
pharyngeal arch The pharyngeal arches, also known as visceral arches'','' are structures seen in the Animal embryonic development, embryonic development of vertebrates that are recognisable precursors for many structures. In fish, the arches are known as the br ...
es, though the eventual fate of these arches varies between
taxa In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanism ...
. In
jawed fish Gnathostomata are the jawed vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few excepti ...
, the first arch develops into the jaws, the second into the hyomandibular complex, with the posterior arches supporting gills. In amphibians and reptiles, many elements are lost including the gill arches, resulting in only the oral jaws and a
hyoid apparatus The hyoid apparatus is the collective term used in veterinary anatomy for the bones which suspend the tongue and larynx The larynx (), commonly called the voice box, is an organ in the top of the neck The neck is the part of the body on many ...
remaining. In mammals and birds, the hyoid is still more simplified. All
basal Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''. Science * Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure * Basal (medicine), a minimal level that is neces ...
vertebrates breathe with
gills A gill () is a respiratory organ that many aquatic Aquatic means relating to water Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent ...

gills
. The gills are carried right behind the head, bordering the posterior margins of a series of openings from the
esophagus The esophagus (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of variety (linguistics), varieties of the English language native to the United State ...

esophagus
to the exterior. Each
gill A gill () is a respiratory organ that many aquatic Aquatic means relating to water Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent ...
is supported by a
cartilagenous
cartilagenous
or
bony
bony
gill arch.
Bony fish Osteichthyes (), popularly referred to as the bony fish, is a diverse taxonomic Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may al ...
have three pairs of arches,
cartilaginous fish Chondrichthyes (; ) is a class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an an ...
have five to seven pairs, and primitive
jawless fish Agnatha (, Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycen ...
have seven. The vertebrate ancestor no doubt had more arches, as some of their
chordate A chordate () is an animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All ...

chordate
relatives have more than 50 pairs of gills.Romer, A.S. (1949): ''The Vertebrate Body.'' W.B. Saunders, Philadelphia. (2nd ed. 1955; 3rd ed. 1962; 4th ed. 1970) In
amphibians Amphibians are ectotherm File:Junonia lemonias DSF by Kadavoor.JPG, ''Junonia lemonias'' is basking under the sun. An ectotherm (from the Ancient Greek, Greek ἐκτός (''ektós'') "outside" and θερμός (''thermós'') "hot") is an ...

amphibians
and some primitive bony
fish Fish are aquatic Aquatic means relating to water Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the ...

fish
, the
larva A larva (plural larvae ) is a distinct juvenile form many animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that f ...
e bear external gills, branching off from the gill arches. These are reduced in adulthood, their function taken over by the gills proper in fish and by
lung The lungs are the primary organs An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tissues can be broadly categorized as parenchyma ...

lung
s in most
amphibians Amphibians are ectotherm File:Junonia lemonias DSF by Kadavoor.JPG, ''Junonia lemonias'' is basking under the sun. An ectotherm (from the Ancient Greek, Greek ἐκτός (''ektós'') "outside" and θερμός (''thermós'') "hot") is an ...

amphibians
. Some amphibians retain the external larval gills in adulthood, the complex internal
gill A gill () is a respiratory organ that many aquatic Aquatic means relating to water Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent ...
system as seen in fish apparently being irrevocably lost very early in the evolution of
tetrapod Tetrapods (; ) are four-limbed animals constituting the superclass Tetrapoda (). It includes extant Extant is the opposite of the word extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a sp ...
s.Clack, J. A. (2002): Gaining ground: the origin and evolution of tetrapods. ''Indiana University Press'', Bloomington, Indiana. 369 pp


Function

The branchial system is typically used for respiration and/or feeding. Many fish have modified posterior gill arches into
pharyngeal jaws Pharyngeal jaws are a "second set" of jaw The jaw is any opposable articulated structure at the entrance of the , typically used for grasping and manipulating food. The term ''jaws'' is also broadly applied to the whole of the structures const ...
, often equipped with specialized
pharyngeal teeth Pharyngeal teeth are teeth A tooth (plural teeth) is a hard, calcified Calcification is the accumulation of calcium salts in a Tissue (biology), body tissue. It normally occurs in the formation of bone, but calcium can be deposited abnorma ...
for handling particular prey items (long, sharp teeth in carnivorous moray eels compared to broad, crushing teeth in durophagous black carp). In amphibians and reptiles, the hyoid arch is modified for similar reasons. It is often used in
buccal pumping Buccal pumping is "breathing with one's cheeks": a method of ventilation used in respiration Respiration may refer to: Biology * Cellular respiration, the process in which nutrients are converted into useful energy in a cell ** Anaerobic respira ...

buccal pumping
and often plays a role in tongue protrusion for prey capture. In species with highly specialized ballistic tongue movements such as chameleons or some plethodontid salamanders, the hyoid system is highly modified for this purpose, while it is often hypertrophied in species which use
suction feeding Aquatic feeding mechanisms face a special difficulty as compared to feeding on land, because the density of water is about the same as that of the prey, so the prey tends to be pushed away when the mouth is closed. This problem was first identifie ...
. Species such as snakes and monitor lizards, whose tongue has evolved into a purely sensory organ, often have very reduced hyoid systems.


Components

The primitive arrangement is 7 (possibly 8) arches, each consisting of the same series of paired (left and right) elements. In order from dorsal-most to ventral-most, these are the pharyngobranchial, epibranchial, ceratobranchial, hypobranchial, and basibranchial. The pharyngobranchials may articulate with the
neurocranium In human anatomy, the neurocranium, also known as the braincase, brainpan, or brain-pan is the upper and back part of the skull The skull is a bone A bone is a rigid tissue Tissue may refer to: Biology * Tissue (biology), an ensemble ...
, while the left and right basibranchials connect to each other (often fusing into a single bone). When part of the hyoid system, the names of the bones are altered by replacing "-branchial" with "-hyal", thus "ceratobranchial" becomes "ceratohyal". * The Basihyal and Basibranchials lie at the midline of the lower edge of the throat. Almost all modern
chondrichthyans Chondrichthyes (; from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10 ...

chondrichthyans
have a single midline basihyal, as do many
teleosts Teleostei (Ancient Greek, Greek: ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts , is, by far, the largest class (biology), infraclass in the class Actinopterygii, the ray-finned fishes, containing 96% of al ...
,
lungfish Lungfish are freshwater rhipidistian Rhipidistia, also known as Dipnotetrapodomorpha, is a clade of lobe-finned fish Sarcopterygii (; from Greek language, Greek: , flesh, and , fin)—sometimes considered synonymous with Crossopterygii (" ...
, and
tetrapodomorphs The Tetrapodomorpha (also known as Choanata) are a clade of vertebrates consisting of tetrapods (four-limbed vertebrates) and their closest sarcopterygii, sarcopterygian relatives that are more closely related to living tetrapods than to living lun ...
. In
tetrapods Tetrapods (; ) are four-limbed animals constituting the superclass Tetrapoda (). It includes extant Extant is the opposite of the word extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a sp ...
, the basihyal is known as the
hyoid bone The hyoid bone (lingual bone or tongue-bone) () is a horseshoe A horseshoe is a fabricated product, normally made of metal A metal (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ε ...
. Basibranchials, which are most common in
osteichthyans
osteichthyans
, have the form of one or more rod-like bones projecting backwards along the throat. * The Ceratohyals and Ceratobranchials lie above their respective basi- components, slanting backwards and upwards. They are often the largest bony components of the gill system, as well as the most essential and abundant components. Small connecting bones known as Hypophyals or Hypobranchials may link the basi- and cerato- components. Paired hypophyals are characteristic of living osteichthyans. Living chondrichthyans lack hypohyals, though several extinct forms are known to have had them. * The Epihyals and Epibranchials lie above their respective cerato- components, slanting forwards, upwards, and often inwards. They are also essential components of the gill system, found in every fish. The epihyal is more commonly known as the hyomandibular, which is homologous to the
stapes The ''stapes'' or stirrup is a bone in the middle ear of humans and other animals which is involved in the conduction of sound vibrations to the inner ear. This bone is connected to the oval window by its Annular ligament of stapes, annular ligam ...
(sometimes known as the columnella) of tetrapods. In filter-feeding fish, the epibranchials often host
gill rakers Gill rakers in fish are bony or cartilaginous Cartilage (cartilaginous tissue) is a resilient and smooth elastic tissue, rubber-like padding that covers and protects the ends of long bone A bone is a Stiffness, rigid tissue (anatomy), tiss ...
, specialized spines projecting backwards to trap plankton. * The Pharhyngobranchials are the most dorsal bony elements of the gill system, connecting to the upper extent of the epibranchials. Living chondrichthyans have large pharyngobranchials which lean backwards and upwards. Osteichthyans, on the other hand, have two different types of pharyngobranchials: Suprapharyngobranchials are toothless structures similar to those of chondrichthyans, while Infrapharyngobranchials often possess teeth and lean inwards and forwards, forming the roof of the throat. A hyoid equivalent of the pharyngobranchial, the Pharyngohyal, is only found in living holocephalans, also known as chimaeras.


Amniotes

Amniotes Amniotes (from Greek ἀμνίον ''amnion'', "membrane surrounding the fetus", earlier "bowl in which the blood of sacrificed animals was caught", from ἀμνός ''amnos'', "lamb") are a clade of tetrapod vertebrates comprising reptiles (c ...
do not have
gills A gill () is a respiratory organ that many aquatic Aquatic means relating to water Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent ...

gills
. The gill arches form as
pharyngeal arch The pharyngeal arches, also known as visceral arches'','' are structures seen in the Animal embryonic development, embryonic development of vertebrates that are recognisable precursors for many structures. In fish, the arches are known as the br ...
es during
embryogenesis An embryo is the early stage of development of a multicellular organism A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms ar ...

embryogenesis
, and lay the basis of essential structures such as
jaw The jaw is any opposable articulated structure at the entrance of the mouth In animal anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organisms and their parts. Ana ...

jaw
s, the
thyroid gland The thyroid, or thyroid gland, is an endocrine gland Endocrine glands are ductless glands of the endocrine system The endocrine system is a messenger system comprising feedback loops of the hormones released by internal glands of an organis ...

thyroid gland
, the
larynx The larynx (), commonly called the voice box, is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exist ...

larynx
, the ''columella'' (corresponding to the
stapes The ''stapes'' or stirrup is a bone in the middle ear of humans and other animals which is involved in the conduction of sound vibrations to the inner ear. This bone is connected to the oval window by its Annular ligament of stapes, annular ligam ...
in
mammals Mammals (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the R ...
) and in mammals the malleus and incus.


References


External links


The Gill Arches: Overview
''
Palaeos Palaeos.com is a web site on biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, ...
''. Retrieved 30 November 2014. {{Authority control Fish anatomy