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Coelacanth
The coelacanths ( ) constitute a now rare order of fish that includes two extant species in the genus ''Latimeria'': the West Indian Ocean coelacanth primarily found near the Comoro Islands off the east coast of Africa (''Latimeria chalumnae'') and the Indonesian coelacanth (''Latimeria menadoensis''). They follow the oldest known living lineage of Sarcopterygii (lobe-finned fish and tetrapods), which means they are more closely related to lungfish, reptiles and mammals than to the common ray-finned fishes. They are found along the coastlines of the Indian Ocean and Indonesia.〔 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 belong to the subclass Actinistia, a group of lobed-finned fish related to lungfish and certain extinct Devonian fish such as osteolepiforms, porolepiforms, rhizodonts, and ''Panderichthys''. Coelacanths were thought to have gone extinct in the Late Cretaceous, around 66 million years ago, but were rediscovered in 1938 off the coast of South Africa.
The coelacanth was long considered a “living fossil” because it was believed to be the sole remaining member of a taxon otherwise known only from fossils, with no close relations alive,〔 and to have evolved into roughly its current form approximately 400 million years ago. Several recent studies have shown that coelacanth body shapes are much more diverse than was previously thought, however.
==Etymology==
The word ''Coelacanth'' is an adaptation of the Modern Latin ''Cœlacanthus'' ("hollow spine"), from the Greek κοῖλ-ος (''koilos ''"hollow" + ἄκανθ-α ''akantha'' "spine"). It is a common name for the oldest living line of Sarcopterygii, referring to the hollow caudal fin rays of the first fossil specimen described and named by Louis Agassiz in 1839.〔 The genus name ''Latimeria'' commemorates Marjorie Courtenay-Latimer who discovered the first specimen in a fish market.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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