The coelacanth (pronounced SEEL-uh-kanth) is an enormous, bottom-dwelling fish that is unlike other living fishes in a number of ways. They belong to an ancient lineage that has been around for more than 360 million years. Coelacanths can reach more than six feet long and weigh about 200 pounds, and they're covered in thick, scaly armor. It's estimated they can live up to 60 years or more.

There are two living species of coelacanth, and both are rare. The West Indian Ocean coelacanth (Latimeria chalumnae) lives off the east coast of Africa, while the Indonesian coelacanth (Latimeria menadoensis) is found in the waters off Sulawesi, Indonesia. They are the sole remaining representatives of a once widespread family of lobe-finned fishes; more than 120 species are known from the fossil record.

Read on to see why coelacanths are unlike any other fish out there.

1. Coelacanths were thought to be extinct until a live one was caught in 1938. Coelacanths were known only from fossils until a live Latimeria chalumnae was discovered off the coast of South Africa in 1938. Until then, they were presumed to have gone extinct in the late Cretaceous period, over 65 million years ago. The second living species of coelacanth, Latimeria menadoensis, was discovered in an Indonesian market in 1997, and a live specimen was caught one year later.

Photo: Ballista, via Wikimedia Commons. Distributed under a CC-BY-SA-3.0 license.

2. Coelacanths might be important for understanding the transition from water to land. Coelacanths were thought to be the ancestors of tetrapods (four-legged, land-living animals), but a recent analysis of the coelacanth genome suggests that lungfish are actually more closely related to tetrapods. The divergence of coelacanths, lungfish, and tetrapods is thought to have occurred about 390 million years ago. Coelacanths might occupy a side branch of the vertebrate lineage, closely related to, yet distinct from, the ancestor of tetrapods.

3. Coelacanths have a unique form of locomotion. One striking feature of the coelacanth is its four fleshy fins, which extend away from its body like limbs and move in an alternating pattern. The movement of alternate paired fins resembles the movement of the forelegs and hindlegs of a tetrapod walking on land.

4. Their jaws are hinged to open wide. Unique to any other living animal, the coelacanth has an intracranial joint, a hinge in its skull that allows it to open its mouth extremely wide to consume large prey.

5. Instead of a backbone, they have a notochord. Coelacanths retain an oil-filled notochord, a hollow, pressurized tube that serves as a backbone. In most other vertebrates, the notochord is replaced by the vertebral column as the embryo develops.

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6. Coelacanths have an electric sense. Coelacanths have a rostral organ in their snouts that is part of an electrosensory system. They likely use electroreception to avoid obstacles and detect prey.

7. They have tiny brains. A coelacanth's brain occupies only 1.5 percent of its cranial cavity. The rest of the braincase is filled with fat.

8. Coelacanths give birth to live young. After an extremely long gestation period, possibly up to three years, female coelacanths give birth to live offspring.

9. They're nocturnal and spend their days resting in caves. During the day, coelacanths rest in caves and crevices. They leave these daytime resting places the same time late each afternoon to feed, mostly on fish and cephalopods. Coelacanths are passive drift feeders, moving lethargically near the ocean bottom and using the current and their flexible lobed fins to move about. During their nightly feeding ventures, they may travel as much as eight kilometers before retreating to a cave before dawn. More than a dozen coelacanths may seek shelter in the same cave; they don't appear to show any aggression toward each other.

Photo: Alberto Fernandez Fernandez, via Wikimedia Commons. Distributed under a CC BY-SA 3.0 license.

10. They don't taste good. People, and most likely other fish-eating animals, don't eat coelacanths because their flesh has high amounts of oil, urea, wax esters, and other compounds that give them a foul flavor and can cause sickness. They're also slimy; not only do their scales ooze mucus, but their bodies exude large quantities of oil.

References and Other Resources:

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Coelacanth (Latimeria chalumnae), Arkive. Accessed January 31, 2015 at www.arkive.org/coelacanth/latimeria-chalumnae/.

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Fricke, H., Schauer, J., Hissmann, K., Kasang, L., and Plante, R. (1991). Coelacanth Latimeria chalumnae aggregates in caves: First observations on their resting habitat and social behavior. Environmental Biology of Fishes 30(3): 281–6. doi:10.1007/BF02028843.

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Latimeria chalumnae (Coelacanth), Encyclopedia of Life. Accessed January 31, 2015 at eol.org/pages/225251/overview.

Lavett Smith, C., Rand, C. S., Schaeffer, B., and Atz, J. W. (1975). Latimeria, the Living Coelacanth, is Ovoviviparous. Science 190(4219): 1105–6. doi:10.1126/science.190.4219.1105.

Street, R. (1999). Latimeria chalumnae, Animal Diversity Web. Accessed January 28, 2015 at animaldiversity.org/accounts/Latimeria_chalumnae/