Coelacanth

The coelacanth (Coelacanthiformes) is a rare species of fish primarily found near the Comoro Islands off the east coast of Africa in the disphotic zone. Since there are only two species of coelacanth and both are threatened, it is the most endangered order of animals in the world. The West Indian Ocean Coelacanth is a critically endangered species. Coelacanths were thought to have become extinct in the Late Cretaceous Period, around 66 million years ago, but were rediscovered in 1938 off the coast of South Africa.

Coelacanths are a part of the lobe-finned fishes group. Externally, several characteristics distinguish the coelacanth from other lobe-finned fish. Coelacanth have a three-lobed back fin, also called a diphycercal tail. A secondary tail extending past the primary tail separates the upper and lower halves of the coelacanth. 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 , a hollow, pressurized tube which is replaced by the vertebral column early in embryonic development in most other vertebrates. The coelacanth heart is shaped differently from that of most modern fish, with its chambers arranged in a straight tube. The coelacanth 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. Coelacanth also possess a unique rostral organ within the ethmoid region of the braincase. The two kidneys, which are fused into one, are located ventrally within the abdominal cavity, posterior to the cloaca.

Coelacanths are considered a poor source of food for humans and likely most other fish-eating animals. According to Wikipedia, ¨coelacanth flesh has high amounts of oil, urea, wax esters, and other compounds that are difficult to digest and can cause diarrhea. Their scales themselves emit 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.¨

 

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