Coelacanth

From Free net encyclopedia

(Redirected from Coelacanthimorpha)

{{Taxobox | color = pink | name = Coelacanths | status = Conservation status: Endangered | image = Coelacanth-bgiu.png | image_width = 200px | image_caption = Latimeria chalumnae | regnum = Animalia | phylum = Chordata | classis = Sarcopterygii | subclassis = Coelacanthimorpha | ordo = Coelacanthiformes | subdivision_ranks = Families | subdivision = See text }}

Coelacanth (meaning "hollow thorn", from the Greek coelia, "κοιλιά" (hollow) and acanthos, "άκανθος" (thorn)); Template:IPA2) is the common name for an order of fish that includes the oldest living lineage of jawed fish known to date. The coelacanths, which are closely related to lungfishes, were believed to have been extinct since the end of the Cretaceous period — until a live specimen turned up off the east coast of South Africa off the Chalumna River in 1938. Since then, they have been found in the Comoros, Sulawesi (Indonesia), Kenya, Tanzania, Mozambique, Madagascar and the St. Lucia Marine Protected Area in South Africa.

Contents

[edit]

Biological characteristics

Image:Latimeria chalumnae01.jpg Coelacanths are lobe-finned fish with the pectoral and anal fins on fleshy stalks supported by bones, and the tail fin divided into three lobes, the middle one of which also includes a continuation of the notochord. Coelacanths have modified cosmoid scales, which are thinner than true cosmoid scales, which can only be found on extinct fish. Coelacanths also have a special electroreceptive device called a rosteral organ in the front of the skull, which probably helps in prey detection.

Coelacanths first appear in the fossil record in the Middle Devonian, about 390 million years ago. Prehistoric species of coelacanth lived in many bodies of water in Late Paleozoic and Mesozoic times.

The average weight of the coelacanth is 176 pounds (80 kg) and they can reach up to 6.5 feet (2 m) in length. Scientists believe individual coelacanths may live as long as 60 years.

They are the only living species known to have a functional intracranial joint, which almost completely separates the front and back halves of the skull internally. Flexure at this joint may aid in the consumption of large prey. Coelacanths are also mucilaginous; their scales release mucus and their bodies continually exude oil. This oil is a laxative, and makes the fish almost inedible unless dried and salted. Their scales are very rough, and the villagers of the Comoros use its scales as sandpaper.

Coelacanth eyes are very sensitive, and have a tapetum lucidum. Coelacanths are almost never caught in the daytime or on nights with full moons, due to the sensitivity of their eyes.

Coelacanths are opportunistic feeders, hunting cuttlefish, squid, snipe eels, small sharks, and other fish found in their deep reef and volcanic slope habitats. Coelacanths are also known to swim head down, backwards and belly up to locate their prey presumably utilizing its rosteral gland. Scientists suspect that one reason this fish has been so successful is that they can slow down their metabolisms at any time, sinking into the less-inhabited depths and minimizing their nutritional requirements in a sort of hibernation mode.

[edit]

Fossil record

Although now represented by only two or three living species, as a group the coelacanths were once very successful with many genera and species that left an abundant fossil record from the Devonian to the end of the Cretaceous period, at which point they apparently suffered a nearly complete extinction, and past which point no fossils are known. It is often claimed that the coelacanth has remained unchanged for millions of years but in fact the living species and even genus are unknown from the fossil record. However, some of the extinct species, particularly those of the last known fossil coelacanth, the Cretaceous genus Macropoma, closely resemble the living species. The most likely reason for the gap is the taxon having become extinct in shallow waters. Deep water fossils are only rarely lifted to levels paleontologists can recover them, making most deep water taxa disappear from the fossil record. The situation is still under investigation by scientists, however.

[edit]

Morphology of the coelacanth skeleton

Image:CTcoelacanth.jpg

View 3D computed tomographic (CT) imagery of the coelacanth skeleton, including labeled images of the intracranial joint, at Digimorph.org.

[edit]

Discovery

[edit]

First find in South Africa

Image:Coelacanth and Courtenay-Latimer.jpg

The first evidence that western scientists had of a modern, living coelacanth was when Marjorie Courtenay-Latimer, curator of a museum in East London, South Africa, discovered a specimen while inspecting local fish catches for unusual marine life in 1938. She was looking at the catch of a fishing boat that had been fishing for sharks near the Chalumna River and saw an odd blue fish fin in the catch. She pulled the fish out of the pile and brought it to the museum to find out what kind of fish it was. Failing to find it in any of her books, she attempted to contact her friend, Professor James Leonard Brierley Smith, but he was away. Unable to preserve the fish, she sent it to a taxidermist. When Smith returned, he immediately recognized it as a coelacanth, known only from fossils. The species was named Latimeria chalumnae in honour of her and the waters in which it was found. The fish was referred to as a "living fossil."

[edit]

Comoros

Image:KMF 5 obv.JPG

A worldwide search was launched for more coelacanths, with a reward of 100 British pounds (a very substantial sum to the average South African fisherman of the time). Fourteen years later, they were found in the Comoros, at first only another single specimen, but later it turned out that the fish was no stranger to local knowledge: the Comorians, in the port of Mutsamudu on the Comorian island of Anjouan, were puzzled that someone would pay big money for what the locals called a gombessa or mame, an inferior (nearly inedible) fish that their fishermen occasionally caught by mistake.

They are now aware of the significance of their endangered species and have a program in place to return any accidentally caught coelacanth to deep water, so that they may survive.

The second specimen, found in 1952 by Comorian fisherman Ahmed Hussain, was originally described as a different species, Malania anjounae (after Daniel François Malan, the South African Prime Minister at the time, who had despatched an SAAF Dakota to fetch the specimen), but it was later discovered that the lack of the first dorsal fin, which was believed to distinguish it from Latimeria, was due to an injury early in the specimen's life. Ironically, Malan was a staunch creationist; on seeing the supposed ancestor of all terrestrial life named after him, his reaction was a startled, "Why it's ugly! Is this where we come from?"

Smith, who died in 1968, wrote his account of the coelacanth story in the book Old Fourlegs, first published in 1956. His book Sea Fishes of the Indian Ocean, illustrated and co-authored by his wife Margaret, remains the standard ichthyological reference for the region.

[edit]

Second species in Indonesia

In 1997, Arnaz and Mark Erdmann were traveling on their honeymoon in Indonesia and saw a strange fish entering the market at Manado Tua, on the island of Sulawesi. Arnaz recognised it as a gombessa, although it was brown, not blue. The Erdmanns did not realise this was a new species until an expert noticed their pictures on the internet. DNA testing revealed that this species, called rajah laut ("King of the Sea") by the Indonesians, is not related to the Comorian population. It was given the scientific name Latimeria menadoensis.

[edit]

St. Lucia Marine Protected Area in South Africa

In South Africa, the search continued on and off over the years. One diver, 46-year-old Riaan Bouwer, lost his life exploring for coelacanths in June of 1998.

On the 28th of October, 2000, just south of the Mozambique border, in Sodwana Bay in the St. Lucia Marine Protected Area, three deep-water divers — Pieter Venter, Peter Timm, and Etienne le Roux — made a dive to 104 metres and unexpectedly spotted a coelacanth.

Calling themselves "SA Coelacanth Expedition 2000", the group returned, this time with photographic equipment, and several additional members. On the 27th of November, after an unsuccessful initial dive the previous day, four members of the group — Pieter Venter, Gilbert Gunn, Christo Serfontein, and Dennis Harding — found three coelacanths. The largest was between 1.5 and 1.8 metres in length, the other two were from 1 to 1.2 metres. The fish swam head-down and appeared to be feeding from the cavern ledges. The group successfully returned with video footage and photographs of the coelacanths.

During the dive however, Serfontein unexpectedly lost consciousness, and 34-year-old Dennis Harding rose to the surface with him in an uncontrolled ascent. Harding complained of neck pains and died from a cerebral embolism while on the boat. Serfontein recovered after being taken underwater for decompression sickness treatment.

In March–April of 2002, the Jago Submersible and Fricke Dive Team descended into the depths off Sodwana and observed 15 coelacanths, one pregnant. Tissue samples were collected using a dart probe.

[edit]

Taxonomy

Coelacanthimorpha or Actinistia are sometimes used to designate the group of Sarcopterygian fish that contains the Coelacanthiformes. The following is a classification of known coelocanth genera and families:

Class Sarcopterygii
Subclass Coelacanthimorpha

[edit]

Trivia

[edit]

References

  • Thompson, Keith S. (1991). Living Fossil: The Story of the Coelacanth, New York: W.W. Norton.
  • Weinberg, Samantha (February 2001). A Fish Caught in Time: The Search for the Coelacanth, Harper.
  • (2004-05-19) "Marjorie Courtenay-Latimer", The Daily Telegraph (London).
  • Pearce, Jeremy (2004-06-07). "Marjorie Courtenay-Latimer, Naturalist, Is Dead at 97", p. B.6, New York Times.
  • Oliver, Myrna (2004-06-13). "Marjorie Courtenay-Latimer, 97; Confirmed Rare Fish's Existence", p. B.16, Los Angeles Times.
[edit]

See also

[edit]

External links

ca:Cel·lacant da:Coelacanth de:Quastenflosser es:Coelacanthimorpha fr:Cœlacanthe id:Coelacanth it:Celacanto jbo:gombesa nl:Coelacanthen ja:シーラカンス pl:Latimeria pt:Celacanto ru:Целакант fi:Latimeria sv:Havstofsstjärt zh:腔棘魚

Retrieved from "http://www.netipedia.com/index.php/Coelacanth"