|
''Latimeria'' is a rare genus of fish that includes two extant species: West Indian Ocean coelacanth (''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 genus of animals in the world. The West Indian Ocean coelacanth is a critically endangered species. ==Biological characteristics== Based on growth rings in their ear bones (otoliths), scientists infer that individual coelacanths may live as long as 80 to 100 years. Coelacanths live as deep as 700 m (2300 ft) below sea level, but are more commonly found at depths of 90 to 200 m. Living examples of ''Latimeria chalumnae'' have a deep blue color which probably camouflages them from prey species; however, the Indonesian species (''L. menadoensis'') is brown. Coelacanth eyes are very sensitive, and have a ''tapetum lucidum''. Coelacanths are almost never caught in the daytime, but have been caught at all phases of the moon. Coelacanth eyes have many rods, receptors in the retina that help animals see in dim light. Together, the rods and tapetum help the fish see better in dark water. Coelacanths are opportunistic feeders, hunting cuttlefish, squid, snipe eels, small sharks, and other fish found in their deep reef and volcanic slope habitats. Coelacanths are also known to swim head down, backwards or belly up to locate their prey, presumably using their rostral glands. Scientists suspect one reason this fish has been so successful is that specimens are able to slow down their metabolisms at will, sinking into the less-inhabited depths and minimizing their nutritional requirements in a sort of hibernation mode. The coelacanths which live near Sodwana Bay, South Africa, rest in caves at depths of 90 to 150 m during daylight hours, but disperse and swim to depths as shallow as 55 m when hunting at night. The depth is not as important as their need for very dim light and, more importantly, for water which has a temperature of 14 to 22°C. They will rise or sink to find these conditions. The amount of oxygen their blood can absorb from the water through the gills is dependent on water temperature. Scientific research suggests the coelacanth must stay in cold, well-oxygenated water or else its blood cannot absorb enough oxygen.〔page 200, Weinberg, Samantha. 2006. A Fish Caught in Time: the Search for the Coelacanth. HarperCollins Publishers, New York, NY.〕 The fish seems to be very well adapted to its environment, which is seen as one of the reasons why it has the slowest evolving genome of all known vertebrates.〔(The 'living fossil' coelacanth fish left behind by evolution )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Latimeria」の詳細全文を読む スポンサード リンク
|