Coelacanths

Lifesize model of adult Latimeria chalumnae (Permission provided by David Noakes)


The coelacanths belong to the Actinistia. Their fins are lobed except the first dorsal fin. The tail is symmetrical and three-lobed and unlike any other fish tail fin. The head bones are peculiar as well, i.e. the maxilla (bone in lower jaw) is completely missing. They have a curious rostral organ filled with gelatinous material that is considered to be an electroreceptor.

As the youngest coelacanth fossils are from the Cretaceous it was generally thought that they had beceome extinct at that time. However in 1938 an African fisherman caught a peculiar fish from the Indian Ocean that was very much alive. Marjorie Courtenay-Latimer was one of the first people to examine the fish and she brought the specimen to her old supervisor J. L. B. Smith at Rhodes University who was amazed to see it was an actinistian. It was so similar to Mezosoic fossil coelacanths that there was no doubt of its taxonomic position. Smith named the 'living fossil' Latimeria chalumnae in honor of Miss Latimer. The finding caused great public and scientific excitement around the globe but it was not until 1952 that further specimens were captured. Since then have 150 specimens been caught, ranging in size from 75 cm to 2 m and the heaviest specimen weighed 80 kilograms. All the specimens have been caught in the Comoros Archipelago between Madagascar and Mosambique in the Southwestern Indian Ocean.

Latimeria chalumnae (Permission provided by Mike Benton)


These massive fish are blue-grayish in colour with irregular white spots on the skin. Their eyes are golden and reflective due to a tapetum lucidum (a membrane at back of the lens) that enhances visual ability in the dim light. Coelacanths are indeed creatures of darkness as they live at depths of 260-300 metres. Hans Fricke and his colleagues captured the coelacanths on film, using a small submarine, in the eighties. They observed six coelacanths at depths between 117 m and 198 m close to the shore of one of the Comoros. They were only seen in the middle of the night and only on or near the bottom. They used their paired fins to swim in a similar fashion as tetrapods use their limbs to walk.

Both fossil specimens of related species and live specimens of female Latimeria show that coelacanths give birth to live youngs. They are ovoviviparous, that is they hatch their eggs internally as the egg shells are too weak to tolerate external conditions. Live specimens have been found with young coelacanths inside the oviduct, each about 30 cm in length. This is evidence for internal fertilization in coelacanths but as no copulatory organs have been observed on the male specimens the copulative method is still a mystery.

Models of Latimeria chalumnae embryos. Notice the nutrition yolk sac on the more developed embryo on the right and the green radient eyes on the embryo on the left (Permission provided by David Noakes)

In 1997 Mark Erdmann and his wife Arnaz visited a fish market in Manado on Sulawesi Island in Indonesia. In the market they saw a strange fish that Mr. Erdmann, a marine biologist, immediately recognised as a coelacanth. They found that it had been caught near some offshore islands close to Manado and that this was not the first one that had been caught. They took photos of the fish but left it there even though they later would regret it. After reassurance from ichthyologists that the fish had indeed been a coelacanth they traveled again to Indonesia to search for more specimens. It took a lot of time and effort but finally they caught an alive coelacanth with the help of indonese fishermen. It was grey-brownish in colour with almost golden spots and greenish, reflective eyes. They took it underwater and filmed it swimming around but as it was clearly dying they decided to keep the specimen. Despite morphological difference from the Comoros coelacanth, DNA tests have shown that it is not significantly different enough to be considered a different species. But it is evident that the coelacanths are more widespread and much remains unknown about these fascinating creatures.



Author: Snorri Sigurdsson (Email: ss4460@bristol.ac.uk)
Last updated: 14 November 2004
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