Coelacanth - biology.

Coelacanth - biology. Coelacanth, large, primitive fish that first appeared more than 350 million years ago and remains relatively unchanged today, earning it the moniker "living fossil." Some biologists speculate that the coelacanth is the closest living relative of the first fish that came ashore to live on land, an event that occurred around 360 million years ago and eventually gave rise to amphibians, reptiles, birds, and mammals. The coelacanth and its cousin, the lungfish, are the only surviving lobe-finned fishes, an ancient group named for the muscular, scale-covered lobe at the base of their fins. By comparison, the more numerous ray-finned fishes have no such lobes at the base of their spiny fins. Two living species of coelacanths have been identified, both found in the deep waters around several volcanic islands in the Indian Ocean. Coelacanths rarely swim at depths of less than 200 m (650 ft), and many live more than 600 m (2,000 ft) below the water's surface. Fossils found in various parts of the world indicate that several species of coelacanths inhabited a variety of water habitats, including lakes, swamps, inland seas, and oceans. The modern coelacanth closely resembles its fossil relatives, having characteristic paired, lobed fins and a three-lobed tail. The fish attains an average length of about 1.5 m (5 ft) and a weight of more than 45 kg (100 lb), although larger specimens have been reported. Its body is bright blue to brownish in color and is covered with small white splotches that resemble the sponges growing in its deep-ocean habitat. Sharp, serrated scales cover the body, and its mouth is lined with several rows of pointed teeth. The coelacanth feeds on smaller fish. A formidable predator, the large fish uses specialized sensory organs to locate its prey. Its eyes are lined with reflecting cells that enhance vision at dimly lit ocean depths. A pressure-sensitive lateral line runs down each side of the body. This row of sensitive cells enables the fish to detect the movements of potential prey in its vicinity. Indentations on either side of the snout lead to a jelly-filled cavity in the skull. This sensory system may help the coelacanth to detect weak electric signals emitted by other living organisms, helping it to further zero in on potential prey. Unlike most fishes, female coelacanths give birth to live young. Coelacanth reproductive behaviors are not well known, but biologists believe that females do not reach sexual maturity until after 20 years of age. After about 13 months gestation, the time between conception and birth, females give birth to between 5 and 25 babies. The young are capable of surviving on their own immediately after birth. Before 1938 it was suspected that the coelacanth had become extinct about 70 million years ago. No sighting of the fish had been reported in recorded history, and coelacanth fossils--common in sedimentary rock from before 70 million years ago--are virtually absent from the more recent fossil record. In December 1938 a fishing trawler off the eastern coast of South Africa captured a living coelacanth, a discovery that took the scientific world by storm. Additional sightings followed, and researchers later learned that people of the region had for many years used coelacanths as food, preparing the meat by drying and salting it. After their rediscovery, coelacanths were observed only in or around the Comoros, a small cluster of volcanic islands between southeastern Africa and Madagascar. As a result, it was believed that coelacanths inhabited only a limited range in the western Indian Ocean. But in 1998 reports of another population, this one more than 10,000 km (6,000 mi) to the east of the Comoros, shattered that long-held belief. First spotted near the eastern Indonesia island of Sulawesi, the newly discovered coelacanth population is the subject of intense scientific investigation. Studies of genetic and morphological structures have shown that this fish differs significantly from its western counterpart and constitutes an entirely new species. Biologists estimate that only 200 to 500 coelacanths remain in the western part of their range (the status of the eastern population is not yet known), and concern for the coelacanth's continued survival is mounting. The coelacanth is classified as vulnerable by the World Conservation Union (also known as the IUCN), an international organization that maintains a global list of vulnerable and endangered species called the Red List. A vulnerable classification means that the species faces a high risk of extinction in the near future. Scientific classification: Coelacanths belong to the family Latimeriidae in the class Osteichthyes, subclass Crossopterygii. The coelacanth found in the western Indian Ocean is classified as Latimeria chalumnae. The coelacanth found in the eastern Indian Ocean is classified as Latimeria menadoensis. Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.