The coelacanths ( ) are fish belonging to the order Actinistia that includes two extant

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

in the

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

Latimeria ''Latimeria'' is a rare genus of fish which contains the only living species of coelacanth. It includes two extant species: the West Indian Ocean coelacanth (''Latimeria chalumnae'') and the Indonesian coelacanth (''Latimeria menadoensis''). T ...

'': the

West Indian Ocean coelacanth The West Indian Ocean coelacanth (''Latimeria chalumnae'') (sometimes known as gombessa, African coelacanth, or simply coelacanth) is a crossopterygian, one of two extant species of coelacanth, a rare order of vertebrates more closely related t ...

(''Latimeria chalumnae''), primarily found near the

Comoro Islands The Comoro Islands or Comoros (Shikomori ''Komori''; ar, جزر القمر , ''Juzur al-qamar''; french: Les Comores) form an archipelago of volcanic islands situated off the southeastern coast of Africa, to the east of Mozambique and northwes ...

off the east coast of Africa, and the

Indonesian coelacanth The Indonesian coelacanth (''Latimeria menadoensis'', Indonesian: ''raja laut'') is one of two living species of coelacanth, identifiable by its brown color. It is listed as vulnerable by the IUCN, while the other species, ''L. chalumnae'' ( We ...

(''Latimeria menadoensis''). The name "coelacanth" originates from the

Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last ...

genus ''

Coelacanthus ''Coelacanthus'' ("Hollow Spine") is a genus of extinct coelacanths that first appeared during the Permian period. It was the first genus of coelacanths described, about a century before the discovery of the extant coelacanth. The order Coelaca ...

'', which was the first scientifically named coelacanth. Coelacanths follow the oldest-known living lineage of

Sarcopterygii Sarcopterygii (; ) — sometimes considered synonymous with Crossopterygii () — is a taxon (traditionally a class or subclass) of the bony fishes known as the lobe-finned fishes. The group Tetrapoda, a mostly terrestrial superclass includi ...

(lobe-finned fish and

tetrapod Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids ( pelycosaurs, extinct t ...

s), which means they are more closely related to

lungfish Lungfish are freshwater vertebrates belonging to the order Dipnoi. Lungfish are best known for retaining ancestral characteristics within the Osteichthyes, including the ability to breathe air, and ancestral structures within Sarcopterygii, i ...

and tetrapods (which includes amphibians, reptiles,

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...

s and mammals) than to

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fishes, is a class of bony fish. They comprise over 50% of living vertebrate species. The ray-finned fishes are so called because their fins are webs of skin supported by bony or h ...

. They are found along the coastline of Indonesia and in the

Indian Ocean The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or ~19.8% of the water on Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia to the east. To the south it is bounded by t ...

. The West Indian Ocean coelacanth is a critically endangered species. The oldest known coelacanth fossils are over 410 million years old. Coelacanths were thought to have become extinct in the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', ...

, around 66 million years ago, but were discovered living off the coast of South Africa in 1938. The coelacanth was long considered a "

living fossil A living fossil is an extant taxon that cosmetically resembles related species known only from the fossil record. To be considered a living fossil, the fossil species must be old relative to the time of origin of the extant clade. Living foss ...

" because scientists thought it was the sole remaining member of a

taxon In biology, a taxon ( back-formation from '' taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular n ...

otherwise known only from fossils, with no close relations alive, and that it evolved into roughly its current form approximately 400 million years ago. However, several more recent studies have shown that coelacanth body shapes are much more diverse than previously thought.

Etymology

The word ''Coelacanth'' is an adaptation of the Modern Latin ''Cœlacanthus'' ("hollow spine"), from the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

κοῖλ-ος (, "hollow") and ἄκανθ-α (, "spine"), referring to the hollow

caudal fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as ...

rays of the first fossil specimen described and named by Louis Agassiz in 1839, belonging to the genus ''

''. The genus name ''Latimeria'' commemorates Marjorie Courtenay-Latimer, who discovered the first specimen.

Discovery

The earliest fossils of coelacanths were discovered in the 19th century. Coelacanths, which are related to

es and

s, were believed to have become extinct at the end of the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

period. More closely related to tetrapods than to the

, coelacanths were considered transitional species between fish and tetrapods. On 23 December 1938, the first ''

'' specimen was found off the east coast of South Africa, off the

Chalumna River The Chalumna River ( xh, Tyolomnqa) is a river in the Eastern Cape, South Africa. It is approximately 78 km long, forming at the confluence of two small rivers, the Qugwala in the West and the Mtyolo in the East. It empties into the Indian ...

(now Tyolomnqa). Museum curator Marjorie Courtenay-Latimer discovered the fish among the catch of a local fisherman. Courtenay-Latimer contacted a Rhodes University ichthyologist, J. L. B. Smith, sending him drawings of the fish, and he confirmed the fish's importance with a famous cable: "Most Important Preserve Skeleton and Gills = Fish Described." Its discovery 66 million years after its supposed extinction makes the coelacanth the best-known example of a

Lazarus taxon In paleontology, a Lazarus taxon (plural ''taxa'') is a taxon that disappears for one or more periods from the fossil record, only to appear again later. Likewise in conservation biology and ecology, it can refer to species or populations tha ...

, an evolutionary line that seems to have disappeared from the fossil record only to reappear much later. Since 1938,

have been found in the Comoros,

Kenya ) , national_anthem = " Ee Mungu Nguvu Yetu"() , image_map = , map_caption = , image_map2 = , capital = Nairobi , coordinates = , largest_city = Nairobi ...

Tanzania Tanzania (; ), officially the United Republic of Tanzania ( sw, Jamhuri ya Muungano wa Tanzania), is a country in East Africa within the African Great Lakes region. It borders Uganda to the north; Kenya to the northeast; Comoro Islands ...

Mozambique Mozambique (), officially the Republic of Mozambique ( pt, Moçambique or , ; ny, Mozambiki; sw, Msumbiji; ts, Muzambhiki), is a country located in southeastern Africa bordered by the Indian Ocean to the east, Tanzania to the north, Malawi ...

Madagascar Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Africa ...

, in

iSimangaliso Wetland Park iSimangaliso Wetland Park (previously known as the Greater St. Lucia Wetland Park) is situated on the east coast of KwaZulu-Natal, South Africa, about 235 kilometres north of Durban by road. It is South Africa's third-largest protected area, ...

, and off the South Coast of Kwazulu-Natal in South Africa. The

specimen was discovered in December 1952. Between 1938 and 1975, 84 specimens were caught and recorded. The second extant species, the

, was described from

Manado Manado () is the capital city of the Indonesian province of North Sulawesi. It is the second largest city in Sulawesi after Makassar, with the 2020 Census giving a population of 451,916 distributed over a land area of 162.53 km2.Badan Pusa ...

North Sulawesi North Sulawesi ( id, Sulawesi Utara) is a province of Indonesia. It is located on the Minahasa Peninsula of Sulawesi, south of the Philippines and southeast of Sabah, Malaysia. It borders the Philippine province of Davao Occidental and Socc ...

Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...

in 1999 by Pouyaud et al. based on a specimen discovered by Mark V. Erdmann in 1998 and deposited at the Indonesian Institute of Sciences (LIPI). Erdmann and his wife Arnaz Mehta first encountered a specimen at a local market in September 1997, but took only a few photographs of the first specimen of this species before it was sold. After confirming that it was a unique discovery, Erdmann returned to Sulawesi in November 1997 to interview fishermen and look for further examples. A second specimen was caught by a fisherman in July 1998, which was then handed to Erdmann.

Description

Latimeria chalumnae The West Indian Ocean coelacanth (''Latimeria chalumnae'') (sometimes known as gombessa, African coelacanth, or simply coelacanth) is a crossopterygian, one of two extant species of coelacanth, a rare order of vertebrates more closely related t ...

'' and '' L. menadoensis'' are the only two known living coelacanth species. Coelacanths are large, plump, lobe-finned fish that can grow to more than and weigh around . They are estimated to live up to 100 years, based on analysis of annual growth marks on scales, and reach maturity around the age of 55; the oldest known specimen was 84 years old at the time of its capture in 1960. Even though their estimated lifetime is similar to humans, gestation can last 5 years, which is 1.5 years more than the deep-sea frilled shark, the previous record holder. They are nocturnal

piscivorous A piscivore () is a carnivorous animal that eats primarily fish. The name ''piscivore'' is derived . Piscivore is equivalent to the Greek-derived word ichthyophage, both of which mean "fish eater". Fish were the diet of early tetrapod evoluti ...

drift-hunters. The body is covered in ctenoid elasmoid scales that act as armor. Coelacanths have eight fins – two dorsal fins, two pectoral fins, two pelvic fins, one anal fin and one caudal fin. The tail is very nearly equally proportioned and is split by a terminal tuft of fin rays that make up its caudal lobe. The eyes of the coelacanth are very large, while the mouth is very small. The eye is acclimatized to seeing in poor light by rods that absorb mostly short wavelengths. Coelacanth vision has evolved to a mainly blue-shifted color capacity. Pseudomaxillary folds surround the mouth and replace the maxilla, a structure absent in coelacanths. Two nostrils, along with four other external openings, appear between the premaxilla and lateral rostral bones. The nasal sacs resemble those of many other fish and do not contain an internal nostril. The coelacanth's rostral organ, contained within the

ethmoid The ethmoid bone (; from grc, ἡθμός, hēthmós, sieve) is an unpaired bone in the skull that separates the nasal cavity from the brain. It is located at the roof of the nose, between the two orbits. The cubical bone is lightweight due to a ...

region of the braincase, has three unguarded openings into the environment and is used as a part of the coelacanth's laterosensory system. The coelacanth's auditory reception is mediated by its inner ear, which is very similar to that of tetrapods and is classified as being a basilar papilla. Coelacanths are a part of the clade

, or the lobe-finned fishes. Externally, several characteristics distinguish coelacanths from other lobe-finned fish. They possess a three-lobed

, also called a trilobate fin or a diphycercal tail. A secondary tail extending past the primary tail separates the upper and lower halves of the coelacanth. ctenoid elasmoid scales act as thick armor to protect the coelacanth's exterior. Several internal traits also aid in differentiating coelacanths from other lobe-finned fish. At the back of the skull, the coelacanth possesses a hinge, the intracranial joint, which allows it to open its mouth extremely wide. Coelacanths also retain an oil-filled notochord, a hollow, pressurized tube which is replaced by a

vertebral column The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordate ...

early in embryonic development in most other vertebrates. The coelacanth's heart is shaped differently from that of most modern fish, with its chambers arranged in a straight tube. The coelacanth's braincase is 98.5% filled with fat; only 1.5% of the braincase contains brain tissue. The cheeks of the coelacanth are unique because the opercular bone is very small and holds a large soft-tissue opercular flap. A spiracular chamber is present, but the spiracle is closed and never opens during development. Also unique to extant coelacanths is the presence of a "fatty lung" or a fat-filled single-lobed

vestigial Vestigiality is the retention, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on co ...

lung, homologous to other fishes' swim bladders. The parallel development of a fatty organ for buoyancy control suggests a unique specialization for deep-water habitats. There are small and hard—but-flexible—plates around the vestigial lung in adult specimens, though not around the fatty organ. The plates most likely had a regulation function for the volume of the lung. Due to the size of the fatty organ, researchers assume that it is responsible for the kidney's unusual relocation. The two kidneys, which are fused into one, are located ventrally within the abdominal cavity, posterior to the cloaca. Latimeria chalumnae

DNA

In 2013, a research group published the genome sequence of the coelacanth in the scientific journal ''

Nature Nature, in the broadest sense, is the physical world or universe. "Nature" can refer to the phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. Although humans are ...

''. Due to their lobed fins and other features, it was once hypothesized that the coelacanth might be the most recent shared ancestor between terrestrial and marine vertebrates. But after sequencing the full genome of the coelacanth, it was discovered that the lungfish is the most recent shared ancestor. Coelacanths and lungfish had already diverged from a common ancestor before the lungfish made the transition to land. Another important discovery made from the genome sequencing is that the coelacanths are still evolving today. While phenotypic similarity between extant and extinct coelacanths suggests there is limited

evolutionary pressure Any cause that reduces or increases reproductive success in a portion of a population potentially exerts evolutionary pressure, selective pressure or selection pressure, driving natural selection. It is a quantitative description of the amount of ...

on these organisms to undergo morphological divergence, they are undergoing measurable genetic divergence. Despite prior studies showing that protein coding regions are undergoing evolution at a substitution rate much lower than other tetrapods (consistent with phenotypic stasis observed between extant and fossil members of the taxa), the non-coding regions subject to higher transposable element activity show marked divergence even between the two extant coelacanth species. This has been facilitated in part by a coelacanth-specific endogenous retrovirus of the Epsilon retrovirus family.

Taxonomy

Cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...

showing the relationships of coelacanth genera after Torino, Soto and Perea, 2021.

Fossil record

According to the fossil record, the divergence of coelacanths,

and

tetrapods Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids (reptiles, including dinosaurs and therefore birds) and synapsids ( pelycosaurs, extinct therapsi ...

is thought to have occurred during the Silurian. Over 100 fossil species of coelacanth have been described. The oldest identified coelacanth fossils are around 420-410 million years old, dating to the early Devonian. Coelacanths were never a diverse group in comparison to other groups of fish, and reached a peak diversity during the

Early Triassic The Early Triassic is the first of three epochs of the Triassic Period of the geologic timescale. It spans the time between Ma and Ma (million years ago). Rocks from this epoch are collectively known as the Lower Triassic Series, which is a un ...

(252-247 million years ago), coinciding with a burst of diversification between the Late Permian and Middle Triassic. Most

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...

coelacanths belong to the order Latimerioidei, which contains two major subdivisions, the marine

Latimeriidae Latimeriidae is the only extant family of coelacanths, an ancient lineage of lobe-finned fish. It contains two extant species in the genus ''Latimeria'', found in deep waters off the coasts of southern Africa and east-central Indonesia. In additio ...

, which contains modern coelacanths, as well as the extinct

Mawsoniidae Mawsoniidae is an extinct family of prehistoric coelacanth fishes which lived during the Triassic to Cretaceous periods. Members of the family are distinguished from their sister group, the Latimeriidae (which contains the living coelacanths of t ...

, which were native to

brackish Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estu ...

, freshwater as well as marine environments. Paleozoic coelacanths are generally small (~30–40 cm in length), while Mesozoic forms were larger. Several specimens belonging to the Jurassic and Creataceous mawsoniid coelcanth genera '' Trachymetopon'' and '' Mawsonia'' likely reached or exceeded in length, making them amongst the largest known fishes of the Mesozoic, and amongst the largest bony fishes of all time. The most recent fossil latimeriid is '' Megalocoelacanthus dobiei'', whose disarticulated remains are found in late

Santonian The Santonian is an age in the geologic timescale or a chronostratigraphic stage. It is a subdivision of the Late Cretaceous Epoch or Upper Cretaceous Series. It spans the time between 86.3 ± 0.7 mya (million years ago) and 83.6 ± 0.7 mya. ...

to middle

Campanian The Campanian is the fifth of six ages of the Late Cretaceous Epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campani ...

, and possibly earliest

Maastrichtian The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval ...

-aged marine strata of the Eastern and Central United States, the most recent mawsoniids are '' Axelrodichthys megadromos'' from early Campanian to early Maastrichtian freshwater continental deposits of France., as well as an indeterminate marine mawsoniid from Morocco, dating to the late Maastrichtian A small bone fragment from the

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located entirel ...

Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name is a combination of the Ancient Greek ''pal ...

has been considered the only plausible post-Cretaceous record, but this identification is based on comparative bone histology methods of doubtful reliability. Living coelacanths have been considered "living fossils" based on their supposedly conservative

morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines * Morphology (archaeology), study of the shapes or forms of artifacts * Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies ...

relative to fossil species; however, recent studies have expressed the view that coelacanth morphologic conservatism is a belief not based on data. Fossils suggest that coelacanths were most morphologically diverse during the Devonian and Carboniferous, while Mesozoic species are generally morphologically similar to each other.

Timeline of genera

ImageSize = width:1200px height:auto barincrement:15px PlotArea = left:10px bottom:50px top:10px right:10px Period = from:-550 till:25 TimeAxis = orientation:horizontal ScaleMajor = unit:year increment:25 start:-550 ScaleMinor = unit:year increment:5 start:-550 TimeAxis = orientation:hor AlignBars = justify Colors = #legends id:CAR value:claret id:ANK value:rgb(0.4,0.3,0.196) id:HER value:teal id:HAD value:green id:OMN value:blue id:black value:black id:white value:white id:paleozoic value:rgb(0.6,0.75,0.55) id:cambrian value:rgb(0.49,0.63,0.33) id:ordovician value:rgb(0,0.57,0.44) id:silurian value:rgb(0.70,0.88,0.71) id:devonian value:rgb(0.8,0.55,0.22) id:carboniferous value:rgb(0.4,0.65,0.6) id:permian value:rgb(0.94,0.25,0.24) id:mesozoic value:rgb(0.38,0.77,0.79) id:triassic value:rgb(0.51,0.17,0.57) id:jurassic value:rgb(0.2,0.7,0.79) id:cretaceous value:rgb(0.5,0.78,0.31) id:cenozoic value:rgb(0.95,0.98,0.11) id:paleogene value:rgb(0.99,0.6,0.32) id:neogene value:rgb(0.999999,0.9,0.1) id:quaternary value:rgb(0.98,0.98,0.50) BarData= bar:eratop bar:space bar:periodtop bar:space bar:NAM3 bar:NAM4 bar:NAM6 bar:NAM13 bar:NAM15 bar:NAM20 bar:NAM21 bar:NAM22 bar:NAM26 bar:NAM29 bar:NAM30 bar:NAM31 bar:NAM32 bar:NAM33 bar:NAM34 bar:NAM35 bar:NAM36 bar:NAM37 bar:NAM38 bar:NAM39 bar:NAM40 bar:NAM41 bar:NAM42 bar:NAM43 bar:NAM44 bar:NAM45 bar:NAM46 bar:NAM47 bar:NAM48 bar:NAM49 bar:NAM50 bar:NAM51 bar:NAM52 bar:NAM53 bar:NAM54 bar:NAM55 bar:NAM56 bar:NAM57 bar:NAM57.1 bar:NAM58 bar:NAM59 bar:NAM60 bar:NAM60.1 bar:NAM60.2 bar:NAM60.3 bar:NAM60.6 bar:NAM61 bar:NAM62 bar:NAM62.1 bar:NAM63 bar:NAM64 bar:NAM65 bar:space bar:period bar:space bar:era PlotData= align:center textcolor:black fontsize:M mark:(line,black) width:25 shift:(7,-4) bar:periodtop from: -542 till: -488.3 color:cambrian text: Cambrian from: -488.3 till: -443.7 color:ordovician text:

Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. T ...

from: -443.7 till: -416 color:silurian text: Silurian from: -416 till: -359.2 color:devonian text: Devonian from: -359.2 till: -299 color:carboniferous text: Carboniferous from: -299 till: -251 color:permian text:

from: -251 till: -199.6 color:triassic text:

Triassic The Triassic ( ) is a geologic period and system (stratigraphy), system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Year#Abbreviations yr and ya, Mya), to the beginning of the Jurassic Period 201.36 ...

from: -199.6 till: -145.5 color:jurassic text:

Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...

from: -145.5 till: -66 color:cretaceous text:

from: -66 till: -23.03 color:paleogene text: Paleogene from: -23.03 till: -2.588 color:neogene text: Neog. from: -2.588 till: 0 color:quaternary text: Q. bar:eratop from: -542 till: -251 color:paleozoic text:

Paleozoic Era The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ''z ...

from: -251 till: -66 color:mesozoic text: Mesozoic Era from: -66 till: 0 color:cenozoic text: Cenozoic PlotData= align:left fontsize:M mark:(line,white) width:5 anchor:till align:left color:devonian bar:NAM3 from:-412.8 till:-411.2 text: Powichthys color:devonian bar:NAM4 from:-408.4 till:-407 text: Youngolepis color:devonian bar:NAM6 from:-407 till:-359.2 text: Onychodus color:devonian bar:NAM13 from:-397.5 till:-359.2 text: Strunius color:devonian bar:NAM15 from:-391.8 till:-374.5 text: Euporosteus color:devonian bar:NAM20 from:-385.3 till:-381.7 text: Miguashaia color:devonian bar:NAM21 from:-385.3 till:-374.5 text: Nesides color:devonian bar:NAM22 from:-381.7 till:-328.3 text: Diplocercides color:devonian bar:NAM26 from:-364.3 till:-359.2 text:

Chagrinia ''Chagrinia'' is a genus of prehistoric lobe-finned fish which lived during the Late Devonian period. The holotype, ''Chagrinia enodis'', was found eroded out of the Chagrin Shale in the Euclid Creek Reservation in Cleveland, Ohio Ohio () ...

color:carboniferous bar:NAM29 from:-345.3 till:-299 text:

Rhabdoderma ''Rhabdoderma'' is an extinct genus of coelacanth fish in the class Sarcopterygii. It lived in the Carboniferous and Early Triassic, and its fossils have been found in Europe, Madagascar and North America. Species * ''Rhabdoderma alderingi'' ...

color:carboniferous bar:NAM30 from:-333.97 till:-328.3 text: Coelacanthopsis color:carboniferous bar:NAM31 from:-328.3 till:-324.9 text: Allenypterus color:carboniferous bar:NAM32 from:-328.3 till:-324.9 text: Caridosuctor color:carboniferous bar:NAM33 from:-328.3 till:-324.9 text: Hadronector color:carboniferous bar:NAM34 from:-328.3 till:-324.9 text: Lochmocereus color:carboniferous bar:NAM35 from:-328.3 till:-324.9 text: Polyosteorhynchus color:carboniferous bar:NAM36 from:-306.5 till:-301.37 text: Synaptotylus color:permian bar:NAM37 from: -299 till:-294.6 text: Ectosteorhachis color:permian bar:NAM38 from:-260 till:-251 text: Changxingia color:permian bar:NAM39 from:-258.0 till:-252 text:

color:permian bar:NAM40 from:-255 till:-251 text: Yonngichthys color:triassic bar:NAM41 from:-251 till:-250.57 text: Laugia color:triassic bar:NAM42 from:-251 till:-248.13 text: Sassenia color:triassic bar:NAM43 from:-251 till:-245 text: Sinocoelacanthus color:triassic bar:NAM44 from:-250.13 till:-249.7 text: Piveteauia color:triassic bar:NAM45 from:-250.13 till:-249.7 text:

Whiteia ''Whiteia'' is an extinct genus of prehistoric coelacanth fish which lived in Madagascar and Canada during the Early Triassic period. Taxonomy The nominal species ''Coelacanthus evolutus'' Beltan, 1980 is a junior synonym of ''Whiteia woodwardi ...

color:triassic bar:NAM46 from:-249.7 till:-248.13 text: Axelia color:triassic bar:NAM47 from:-249.7 till:-248.13 text: Mylacanthus color:triassic bar:NAM48 from:-249.7 till:-248.13 text: Scleracanthus color:triassic bar:NAM49 from:-249.7 till:-248.13 text: Wimania color:triassic bar:NAM50 from:-245 till:-237 text: Garnbergia color:triassic bar:NAM51 from:-242 till:-237 text:

Heptanema ''Heptanema'' is an Extinction, extinct genus of prehistoric coelacanth from the Middle Triassic (Ladinian) of northern Italy and Switzerland. The Type species, type and only species is ''Heptanema paradoxum''. Woodward (1891) suggested that '' ...

color:triassic bar:NAM52 from:-237 till:-234 text: Alcoveria color:triassic bar:NAM53 from:-237 till:-234 text: Ticinepomis color:triassic bar:NAM54 from:-237 till:-228 text: Hainbergia color:triassic bar:NAM55 from:-220.3 till:-216.5 text: Graphiuricthys color:jurassic bar:NAM56 from:-199.6 till:-191 text: Holophagus color:jurassic bar:NAM57 from:-199 till:-163.5 text: Trachymetopon color:jurassic bar:NAM57.1 from:-163.5 till:-157.3 text:

Swenzia ''Swenzia'' is an extinct genus of coelacanthid fish from the late Jurassic of France.Clement, G. 2005. A new coelacanth (Actinistia, Sarcopterygii) from the Jurassic of France, and the question of the closest relative fossil to Latimeria. Journ ...

color:jurassic bar:NAM58 from:-161.2 till:-145.5 text: Lualabaea color:jurassic bar:NAM59 from:-152 till:-145 text: Undina color:jurassic bar:NAM60 from:-150.8 till:-149.03 text: Coccoderma color:jurassic bar:NAM60.1 from:-150.8 till:-149.03 text: Libys color:cretaceous bar:NAM60.2 from:-150 till:-95 text: Mawsonia color:cretaceous bar:NAM60.3 from:-112 till:-71.5 text:

Axelrodichthys ''Axelrodichthys'' is an extinct genus of mawsoniid coelacanth from the Cretaceous of Africa, North and South America, and Europe. Several species are known, the remains of which were discovered in the Lower Cretaceous (Aptian-Albian) of Brazil ...

color:cretaceous bar:NAM60.6 from:-112 till:-79.2 text: Macropoma color:cretaceous bar:NAM61 from:-99.6 till:-93.5 text: Macropomoides color:cretaceous bar:NAM62 from:-86.3 till:-71.5 text: Megalocoelacanthus color:cretaceous bar:NAM62.1 from:-67 till:-65 text: Mawsoniidae indeterminate color:cretaceous bar:NAM63 from:-65 till:-64 text: Coelacanthiformes indeterminate? color:quaternary bar:NAM64 from:-1 till:0 text:

PlotData= align:center textcolor:black fontsize:M mark:(line,black) width:25 bar:period from: -542 till: -488.3 color:cambrian text: Cambrian from: -488.3 till: -443.7 color:ordovician text:

from: -251 till: -199.6 color:triassic text:

from: -199.6 till: -145.5 color:jurassic text:

from: -145.5 till: -66 color:cretaceous text:

from: -66 till: -23.03 color:paleogene text: Paleogene from: -23.03 till: -2.588 color:neogene text: Neog. from: -2.588 till: 0 color:quaternary text: Q. bar:era from: -542 till: -251 color:paleozoic text:

from: -251 till: -66 color:mesozoic text: Mesozoic Era from: -66 till: 0 color:cenozoic text: Cenozoic

Distribution and habitat

The current coelacanth range is primarily along the eastern African coast, although ''Latimeria menadoensis'' was discovered off Indonesia. Coelacanths have been found in the waters of Kenya, Tanzania, Mozambique, South Africa, Madagascar, Comoros and Indonesia. Most ''Latimeria chalumnae'' specimens that have been caught have been captured around the islands of Grande Comore and Anjouan in the Comoros Archipelago (Indian Ocean). Though there are cases of ''L. chalumnae'' caught elsewhere, amino acid sequencing has shown no big difference between these exceptions and those found around Comore and Anjouan. Even though these few may be considered strays, there are several reports of coelacanths being caught off the coast of Madagascar. This leads scientists to believe that the endemic range of ''Latimeria chalumnae'' coelacanths stretches along the eastern coast of Africa from the Comoros Islands, past the western coast of Madagascar to the South African coastline. Mitochondrial DNA sequencing of coelacanths caught off the coast of southern Tanzania suggests a divergence of the two populations some 200,000 years ago. This could refute the theory that the Comoros population is the main population while others represent recent offshoots. A live specimen was seen and recorded on video in November 2019 at 69 m off the village of Umzumbe on the South Coast of KwaZulu-Natal, about 325 km south of the iSimangaliso Wetland Park. This is the farthest south since the original discovery, and the second shallowest record after 54 m in the Diepgat Canyon. These sightings suggest that they may live shallower than previously thought, at least at the southern end of their range, where colder, better-oxygenated water is available at shallower depths. The geographical range of the Indonesia coelacanth, ''Latimeria menadoensis'', is believed to be off the coast of Manado Tua Island, Sulawesi,

in the

Celebes Sea The Celebes Sea, (; ms, Laut Sulawesi, id, Laut Sulawesi, fil, Dagat Selebes) or Sulawesi Sea, of the western Pacific Ocean is bordered on the north by the Sulu Archipelago and Sulu Sea and Mindanao Island of the Philippines, on the east b ...

. Key components confining coelacanths to these areas are food and temperature restrictions, as well as ecological requirements such as caves and crevices that are well-suited for drift feeding. Teams of researchers using submersibles have recorded live sightings of the fish in the Sulawesi Sea as well as in the waters of

Biak Biak is an island located in Cenderawasih Bay near the northern coast of Papua, an Indonesian province, and is just northwest of New Guinea. Biak is the largest island in its small archipelago, and has many atolls, reefs, and corals. The large ...

in Papua.

Anjouan Anjouan (; also known as Ndzuwani or Nzwani, and historically as Johanna or Hinzuan) is an autonomous high island in the Indian Ocean that forms part of the Union of the Comoros. Its chief town is Mutsamudu and, , its population is around 277,500. ...

Island and the Grande Comore provide ideal underwater cave habitats for coelacanths. The islands' underwater volcanic slopes, steeply eroded and covered in sand, house a system of caves and crevices which allow coelacanths resting places during the daylight hours. These islands support a large benthic fish population that helps to sustain coelacanth populations. During the daytime, coelacanths rest in caves anywhere from 100 to 500 meters deep. Others migrate to deeper waters. The cooler waters (below 120 meters) reduce the coelacanths' metabolic costs. Drifting toward reefs and night feeding saves vital energy. Resting in caves during the day also saves energy that otherwise would be expended to fight currents. Coelacanth1

Behavior

Coelacanth locomotion is unique. To move around they most commonly take advantage of up- or down-wellings of current and drift. Their paired fins stabilize movement through the water. While on the ocean floor, they do not use the paired fins for any kind of movement. Coelacanths generate thrust with their caudal fins for quick starts. Due to the abundance of its fins, the coelacanth has high maneuverability and can orient its body in almost any direction in the water. They have been seen doing headstands as well as swimming belly up. It is thought that the

rostral organ The rostral organ of the coelacanth or similar in many other fish such as Anchovy is a large gel-filled cavity in the snout, with three pairs of canals to the outside. It is surrounded by an insulating layer of adipose tissue and innervated by the ...

helps give the coelacanth

electroreception Electroreception and electrogenesis are the closely-related biological abilities to perceive electrical stimuli and to generate electric fields. Both are used to locate prey; stronger electric discharges are used in a few groups of fishes to st ...

, which aids in movement around obstacles. Coelacanths are fairly peaceful when encountering others of their kind, remaining calm even in a crowded cave. They do avoid body contact, however, withdrawing immediately if contact occurs. When approached by foreign potential predators (e.g. a submersible), they show panic flight reactions, suggesting that coelacanths are most likely prey to large deepwater predators. Shark bite marks have been seen on coelacanths; sharks are common in areas inhabited by coelacanths. Electrophoresis testing of 14 coelacanth enzymes shows little genetic diversity between coelacanth populations. Among the fish that have been caught were about equal numbers of males and females. Population estimates range from 210 individuals per population to 500 per population. Because coelacanths have individual color markings, scientists think that they recognize other coelacanths via electric communication.

Feeding

Coelacanths are nocturnal piscivores that feed mainly on benthic smaller fish and various cephalopods. They are "passive drift feeders", slowly drifting along currents with only minimal self-propulsion, eating whatever prey they encounter. Coelacanths also use their rostral organ for its electroreption to be able to detect nearby prey in low light settings.

Life history

Coelacanths are

ovoviviparous Ovoviviparity, ovovivipary, ovivipary, or aplacental viviparity is a term used as a "bridging" form of reproduction between egg-laying oviparous and live-bearing viviparous reproduction. Ovoviviparous animals possess embryos that develop insi ...

, meaning that the female retains the fertilized eggs within her body while the embryos develop during a gestation period of five years. Typically, females are larger than the males; their scales and the skin folds around the cloaca differ. The male coelacanth has no distinct copulatory organs, just a cloaca, which has a urogenital papilla surrounded by erectile caruncles. It is hypothesized that the cloaca everts to serve as a copulatory organ. Coelacanth eggs are large, with only a thin layer of membrane to protect them. Embryos hatch within the female and eventually are born alive, which is a rarity in fish. This was only discovered when the American Museum of Natural History dissected its first coelacanth specimen in 1975 and found it pregnant with five embryos. Young coelacanths resemble the adult, the main differences being an external yolk sac, larger eyes relative to body size and a more pronounced downward slope of the body. The juvenile coelacanth's broad yolk sac hangs below the pelvic fins. The scales and fins of the juvenile are completely matured; however, it does lack

odontode Odontodes, or dermal teeth, are hard structures found on the external surfaces of animals or near internal openings. They consist of a soft pulp surrounded by dentine and covered by a mineralized substance such as enamel, a structure similar to th ...

s, which it gains during maturation. A study that assessed the paternity of the embryos inside two coelacanth females indicated that each clutch was sired by a single male. This could mean that females mate

monandrous In botanical terms, monandrous simply means to have a single stamen. In orchids A distinction between monandrous and other flowers is particularly relevant in the classification of orchids. The monandrous orchids form a clade consisting of the s ...

ly, i.e. with one male only.

Polyandry Polyandry (; ) is a form of polygamy in which a woman takes two or more husbands at the same time. Polyandry is contrasted with polygyny, involving one male and two or more females. If a marriage involves a plural number of "husbands and wives ...

, female mating with multiple males, is common in both plants and animals and can be advantageous (e.g. insurance against mating with an infertile or incompatible mate), but also confers costs (increased risk of infection, danger of falling prey to predators, increased energy input when searching for new males).

Conservation

Because little is known about the coelacanth, the conservation status is difficult to characterize. According to Fricke et al. (1995), it is important to conserve the species. From 1988 to 1994, Fricke counted some 60 individuals of ''L. chalumnae'' on each dive. In 1995 that number dropped to 40. Even though this could be a result of natural population fluctuation, it also could be a result of overfishing. The IUCN currently classifies ''L. chalumnae'' as " critically endangered", with a total population size of 500 or fewer individuals. ''L. menadoensis'' is considered Vulnerable, with a significantly larger population size (fewer than 10,000 individuals). The major threat towards the coelacanth is the accidental capture by fishing operations, especially commercial deep-sea

trawling Trawling is a method of fishing that involves pulling a fishing net through the water behind one or more boats. The net used for trawling is called a trawl. This principle requires netting bags which are towed through water to catch different spec ...

. Coelacanths usually are caught when local fishermen are fishing for

oilfish The oilfish (''Ruvettus pretiosus'') is a species of snake mackerel fish with a cosmopolitan distribution in tropical and temperate oceans. It can be found at depths of from , usually between . It can grow to a length of TL (nearly 10 feet) ...

. Fishermen sometimes snag a coelacanth instead of an oilfish because they traditionally fish at night, when oilfish (and coelacanths) feed. Before scientists became interested in coelacanths, they were thrown back into the water if caught. Now that they are recognized as important, fishermen trade them to scientists or other officials. Before the 1980s, this was a problem for coelacanth populations. In the 1980s, international aid gave fiberglass boats to the local fishermen, which moved fishing beyond the coelacanth territories into more productive waters. Since then, most of the motors on the boats failed, forcing the fishermen back into coelacanth territory and putting the species at risk again. Methods to minimize the number of coelacanths caught include moving fishers away from the shore, using different laxatives and malarial salves to reduce the demand for oilfish, using coelacanth models to simulate live specimens, and increasing awareness of the need for conservation. In 1987 the Coelacanth Conservation Council advocated the conservation of coelacanths. The CCC has branches located in Comoros, South Africa, Canada, the United Kingdom, the U.S., Japan, and Germany. The agencies were established to help protect and encourage population growth of coelacanths. A "deep release kit" was developed in 2014 and distributed by private initiative, consisting of a weighted hook assembly that allows a fisherman to return an accidentally caught coelacanth to deep waters where the hook can be detached once it hits the seafloor. Conclusive reports about the effectiveness of this method are still pending. In 2002, the South African Coelacanth Conservation and Genome Resource Programme was launched to help further the studies and conservation of the coelacanth. This program focuses on biodiversity conservation, evolutionary biology, capacity building, and public understanding. The South African government committed to spending R10 million on the program. In 2011, a plan was made for a Tanga Coelacanth Marine Park to conserve biodiversity for marine animals including the coelacanth. The park was designed to reduce habitat destruction and improve prey availability for endangered species. File:Coelacanth sea world.JPG, Coelacanth File:Coelacanth in Kuwait by Prof Dr Norman Ali Khalaf July 2019.jpg, Coelacanth at Abdallah Al Salem Cultural Center in Kuwait

Human consumption

Coelacanths are considered a poor source of food for humans and likely most other fish-eating animals. Coelacanth flesh has large amounts of oil,

urea Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid. Urea serves an important ...

wax ester A wax ester (WE) is an ester of a fatty acid and a fatty alcohol. Wax esters comprise the main components of three commercially important waxes: carnauba wax, candelilla wax, and beeswax.. Wax esters are formed by combining one fatty acid with on ...

s, and other compounds that give the flesh a distinctly unpleasant flavor, make it difficult to digest, and can cause

diarrhea Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration often begin w ...

. Their scales themselves secrete mucus, which combined with the excessive oil their bodies produce, make coelacanths a slimy food. Where the coelacanth is more common, local fishermen avoid it because of its potential to sicken consumers. As a result, the coelacanth has no real commercial value apart from being coveted by museums and private collectors.

Cultural significance

Because of the surprising nature of the coelacanth's discovery, they have been a frequent source of inspiration in modern artwork, craftsmanship, and literature. At least 22 countries have depicted them on their postage stamps, particularly the Comoros, which has issued 12 different sets of coelacanth stamps. The coelacanth is also depicted on the 1000 Comorian franc banknote, as well as the 5 CF coin.

References

External links

Anatomy of the coelacanth
by PBS (

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'Living fossil' coelacanth genome sequenced
BBC News Science & Environment; 17 April 2013 {{Authority control Latimeriidae Live-bearing fish Ovoviviparous fish Fish of the Comoros Fish of Indonesia Fish of Kenya Fish of Mozambique Marine fish of South Africa Fish of Tanzania Extant Early Devonian first appearances 1938 in biology Taxa named by Lev Berg