Coelacanths

Coelacanths ( SEE-lə-kanth) are an ancient group of lobe-finned fish (Sarcopterygii) in the class Actinistia. As sarcopterygians, they are more closely related to lungfish and tetrapods (the terrestrial vertebrates including living amphibians, reptiles, birds and mammals) than to ray-finned fish. There is only a single living genus, Latimeria, with two described species.

The name coelacanth originates from the Permian genus Coelacanthus, which was the first scientifically named genus of coelacanths (in 1839), becoming the type genus of Coelacanthiformes as other species were discovered and named. Well-represented in freshwater and marine deposits from as early as the Devonian period (more than 410 million years ago), they were thought to have become extinct in the Late Cretaceous, around 66 million years ago.

The first living coelacanth species to be discovered, Latimeria chalumnae, the West Indian Ocean coelacanth, was described from specimens fished off the coast of South Africa from 1938 onward; they are now also known to inhabit the seas around the Comoro Islands off the east coast of Africa. The Indonesian coelacanth Latimeria menadoensis was discovered in the late 1990s, and inhabits the seas of Eastern Indonesia, from the northern region of Central Sulawesi and eastwards to Papua. Genetic studies suggests that the Indonesian population may in fact encompass more than one distinct species.

The two species within the extant genus Latimeria are often considered examples of "living fossils" in popular science because they were considered the sole remaining members of a taxon otherwise known only from fossils (a biological relict), and that they had retained the same bodyplan that had evolved approximately 400 million years ago. However, fossil coelacanths have shown body shapes and niches that were much more diverse than what was previously thought, and often differed significantly from Latimeria; some species seemed to have been active, pelagic swimmers like Rebellatrix. The family Mawsoniidae has species which moved between freshwater and saltwater.