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The Coelacanth fish- living fossil today

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Description

The scientific name of the Coelacanth fish is and bears the scientific name Latimeria Chalumnae and it comes from the one who discovered in 1938 Marjorie Courtenay Latimer, the curator of a small museum in the port town of East London, while she was visiting a fisherman who would let her search through his boat's catch for interesting specimens. When captured, the specimen weighed approximately 160 pounds and measured slightly less than 5  feet in total length.

The specimen is identified as Latimeria chalumnae and bears the catalog number USNM 205871. After Marjorie brought back the specimen to the museum and she compared it against other known fish images, she realized what she had was no ordinary fish and in fact is a new species The Professor J.L.B. Smith, at Rhodes University, Grahamstown, analyzed the drawings provided by Marjorie and he confirmed that the creature she had discovered was indeed a prehistoric fish, a Coelacanth.

Coelacanth_Latimeria_fish_swimming

While there have been enough sightings of the creature to indicate that there is more than one area where the species exists, it remains a highly protected and mysterious animal, a living fossil which may, or may not be the only creature from our past which has survived millions of years of evolution.



The classification of coelacanths is a quite difficult with more than one variation in the class category. Kingdom: Animalia, Phylum: Chordata,
Class: Pices (fishes),
Sub class: Gnathostomata- jawed fishes,
Sub class: Teleostei- bony fishes (though cartilaginous, coelacanths are usually classed with the teleosts), Sub class: Sarcopterygii (lobed-finned fishes),
Order: Crossopterygii, Family: Actinistia (coelacanths),
Gennus: Latimeria, Species: chalumnae and menadoensis.   

The coelacanth appears to be a cousin of Eusthenopteron, the fish once credited with growing legs and coming ashore-360 million years ago.

Coelacanth_Latimeria_fish_evolution_Fishapods


Today, scientists prefer to cite the tongue-twisting fossil candidates: icthyostega, panderichthys, acanthotega, and the newly discovered Tiktaalik roseae (2004), as the ancestor(s) of all tetrapods-amphibians, reptiles, and mammals, including ourselves. The Coelacanth fish is also the closest link between fish and the first amphibian creatures which made the transition from sea to land in the Devonian period (408-362 Million Years Ago). That such a creature could have existed for so long is nearly incredible, but some say that the cold depths of the West Indian Ocean at which the Coelacanth thrives, and the small number of predators it has, may have helped the species survive eons of change.

 

Characteristics

Numerous characteristics are unique to the coelacanth among living fishes. Among them are the presence of a "rostral organ" in the snout that is part of the electrosensory system, and an intracranial joint or "hinge" in the skull that allows the anterior portion of the cranium to swing upwards, greatly enlarging the gape of the mouth. Neither of these characters exists in any other living vertebrate.

coelacanth_5


Other unique anatomical features include a hollow fluid-filled "notochord" (a primitive feature in vertebrates) underlying the spinal cord and extending the length of the body, vertebrae that are incompletely formed or totally lacking bony centra, an oil-filled gas bladder, fleshy "lobed" or limb-like fins that are internally supported by bone, and paired fins that move in a synchronized tetrapod-like pattern.  The sucking maws of jawless predecessors have transformed, through a modification of one of the gill arches, into hinged, rigid structures with teeth on the bottom ridge and upper palate- true jaws.

Coelacanth_Latimeria_fish_body_drawings

The tiny brain, is encased in a hardened skull, which hinges in the middle to increase the gape of the mouth while feeding (a feature also found in frogs!). The eyes are well developed, with reflecting cells called tapita to enhance night vision. A chambered heart pumps blood in prototype to our own. Three indentations on either side of the snout lead to a peculiar cavity, a jelly-filled rostral organ, which very likely functions as an electro-receptor to help in the location of prey. Along the sides a pressure sensitive lateral line is well developed to sense the proximity of other fishes and surrounding structures- no doubt useful in the submarine caves where coelacanths pass their days.

Latimeria_menadoensis

Two back, or dorsal, fins and one protruding beneath the nape of the tail are complimented by paired lobed pectoral and pelvic fins. These contain in their trunks bones mimicking those of Eusthenopteron which later developed into arms and legs. While coelacanths have not been observed to "walk" on the bottom, their pectoral and pelvic fins can be seen as "pre-adaptations" to land locomotion. Used under water their action maintains stability and balance. But in their cousin Eusthenopteron, the same action became four-legged land walking. The body is covered in cosmoid scales that act as armor. Coelacanths have 8 fins - 2 dorsal fins, 2 pectoral fins, 2 pelvic fins, 1 anal fin, and 1 caudal fin. The tail is very nearly equally proportioned and is split by a terminal tuft of fin rays that make up the caudal lobe of the tail.

Coelacanth_Latimeria_fish_anatomy_skematic

The eyes of the coelacanth are very large, while the mouth is very small. The eye is acclimatized to seeing in dark light by having rods that absorb mostly low wavelengths. The vision of Coelacanths has evolved to a mainly blue-shifted color capacity. The backbone of this fish is composed of a fluid-filled cartilaginous tube, which provides a firm yet flexible support for muscles.


Hollow fin spines, identified in fossils, are what got the fish its name- "coelacanth" which literally means 'hollow spine'from the Greek The coelacanth's true evolutionary relationships are a matter of controversy. There are several competing hypotheses and many unresolved questions, in large part owing to the many unusual characters found in coelacanths. Experts largely agree that coelacanths are primitive bony fishes (as opposed to a cartilaginous fishes, such as sharks and rays), and that their closest living relatives are the primitive lungfishes (known from freshwaters of South Africa, Australia and South America), but they disagree on the exact placement of the coelacanth in the evolutionary history of vertebrates.


Coelacanth-cave

Coelacanths might best be described as occupying a side branch in the basal portion of the vertebrate lineage, closely related to but distinct from the ancestor of tetrapods (four-legged vertebrates). The rostral organ of the coelacanth is contained within the ethmoid region of the braincase. It has three unguarded openings into the environment. The rostral organ is used as a part of the coelacanths’ laterosensory system Today's coelacanths can reach almost six feet (2 meters) in length and weigh up to 150 or more lbs,(the giant Mozambique female shown on this site was 180 centimeters long and 95kg) but they are usually somewhat smaller, particularly the males, which average under 165cm. Scientists believe individual coelacanths may live as long as 60 years, but there is still confusion as to how many scale growth rings are laid down each year: one or two. The answer would drastically affect the life span estimate Coloration is dark blue with distinctive white flecks that can even be used by researchers to designate individuals. (Indonesian coelacanths may be more brown than blue). The white flecks afford camouflage against a backdrop of dark lava walls encrusted with white oyster shells.

 

Habitat

Until recent years, living coelacanths were known only from the western Indian Ocean, primarily from the Comoros Islands, which are situated in the Western Indian Ocean between Madagascar and the east coast of Africa, but also occur elsewhere along eastern Africa and in Indonesia but in September 1997 and again in July 1998, coelacanths were captured in northern Sulawesi, Indonesia, nearly 6,000 miles to the east of the Comoros.

Coelacanth_Comore_Island_Map_discovery

The Indonesian discovery was made by Mark V. Erdmann, then a doctoral student studying coral reef ecology in Indonesia. In the Indian Ocean only one capture (the original one in 1938) is from South Africa and this specimen was long thought to be a stray from the Comoron population. However, resident South African coelacanths have been sighted recently in deep canyons, initially by divers using mixed gas "rebreathers," and subsequently by scientists using a submersible.

Elsewhere in the Western Indian Ocean specimens have been captured off the west coast of Madagascar and off Mozambique and Kenya, the latter representing the most northern locality record along the African coast. Two confirmed captures (only one specimen preserved) occurred in recent years in Indonesia, off the island of Manado Tua at the northern tip of Sulawesi. These captures were followed by sightings of two more specimens from a submersible approximately 225 miles southwest of Manado Tua.

 

Diet

The coelacanth is a "passive drift feeder," moving slowly and passively near the substrate where it feeds primarily on cephalopods (cuttlefish, squid, and octopus) and fishes. It is capable of moving quickly and may do so when capturing prey or avoiding danger Coelacanths are opportunistic feeders, scraping up prey probably on or near the bottom. Stomach contents have included lantern fishes, stout beard fishes, cardinal fishes, cuttle fishes, deep water snappers, squids, deep-sea witch eels, snipe eels, swell sharks, and other fishes normally found in their deep reef and volcanic slope habitats.

Reproduction The mode of reproduction is ovoviviparity. This involves internal fertilization of an egg, followed by a gestation period thought to be about a year in duration during which time the embryo feeds off the yolk sac of the egg, culminating in the live birth of a fully formed juvenile. Only two females carrying young, or "pups" as they are called, have been captured. One female contained five full-term pups, each approximately 14" long, and the other had twenty six pups of approximately the same size. The latter specimen is also the largest recorded coelacanth, weighing nearly 200 lbs. and reaching 6 feet in length.




Interesting info's

 The Coelacanth is the only living example of the fossil Coelacanth fishes Actinista. They are also the closest link between fish and the first amphibian creatures which made the transition from sea to land in the Devonian period (408-362 Million Years Ago).
 The backbone of this fish is composed of a fluid-filled cartilaginous tube, which provides a firm yet flexible support for muscles. Hollow fin spines, identified in fossils, are what got the fish its name- "coelacanth" which literally means 'hollow spine' from the Greek.
 Coelacanth scales are thick, and lined with serrated rows of hardened toothpick-pointed denticles. Perhaps most distinctive of all is the trilobated tail with its extra trunk and fin protruding from the middle. It was this feature that made fossil coelacanths so easily recognizable and helped clinch the case for the identification of the first living specimen.
 The limb-like second dorsal and anal fins, the unusual 3-part caudal fin, and the raised profile of the notochord extending out onto the tail.Note the limb-like pectoral fin, large eye and teeth.
 The tiny brain is encased in a hardened skull, which hinges in the middle to increase the gape of the mouth while feeding (a feature also found in frogs!) .
 The eyes are well developed, with reflecting cells called tapita to enhance night vision.
 A chambered heart pumps blood in prototype to our own. Three indentations on either side of the snout lead to a peculiar cavity, a jelly-filled rostral organ, which very likely functions as an electro-receptor to help in the location of prey.   Fins beneath the nape of the tail are complimented by paired lobed pectoral and pelvic fins,and contain in their trunks bones mimicking those of Eusthenopteron which later developed into arms and legs.
 While coelacanths have not been observed to "walk" on the bottom, their pectoral and pelvic fins can be seen as "pre-adaptations" to land locomotion.
 Locomotion of the coelacanths is unique to their kind. To move around, coelacanths most commonly take advantage of up or downwellings of the current and drift. They use their paired fins to stabilize their movement through the water. While on the ocean floor their paired fins are not used for any kind of movement

    

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Sources 
http://www.panoramio.com/photo/33347917
http://animals.nationalgeographic.com/animals/fish/coelacanth/ http://www.mnh.si.edu/highlight/coelacanth/usnm_specimens.htm
http://www.mnh.si.edu/highlight/coelacanth/
http://extinctanimal.com/the_coelacanth.htm
http://gombessa.tripod.com/index.html http://www.pibburns.com/cryptost

http://www.bbc.co.uk/programmes/p004j61g http://www.answersincreation.org/curriculum/history/earth_history_c6_devonian_fish.htm
http://www.stampcommunity.org http://gombessa.tripod.com/id7.html
http://www.dipity.com http://commons.wikimedia.org
http://en.wikipedia.org/wiki/Coelacanth
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