Coelacanth

Coelacanths are an ancient group of lobe-finned fish called Actinistia. They are more closely related to lungfish and land animals like amphibians, reptiles, birds, and mammals than to most other fish. Today, there is only one living genus, Latimeria, which includes two known species.

The name coelacanth comes from an old Permian fish genus named Coelacanthus in 1839. For a long time, scientists thought coelacanths went extinct about 66 million years ago during the Late Cretaceous. But in 1938, people found a living species, Latimeria chalumnae, off the coast of South Africa. We now know this fish also lives near the Comoro Islands. Later, in the late 1990s, another species, Latimeria menadoensis, was found in the seas of Eastern Indonesia, from Manado to Papua.

Because coelacanths were thought to be extinct and then found alive, they are often called a "living fossil". They have looked much the same for about 400 million years. However, fossils show that ancient coelacanths had many different shapes and lived in many different ways, unlike the two living species we know today.

Etymology

The word Coelacanth comes from Latin and Greek words meaning "hollow spine". It refers to a special feature found in the first fossil of this fish that was studied. This fossil was named by a scientist named Louis Agassiz in 1839.

The name Latimeria honors Marjorie Courtenay-Latimer, who found the first living example of this amazing fish.

Discovery

The earliest fossils of coelacanths were found in the 1800s. People thought coelacanths had gone extinct at the end of the Cretaceous period. They are more closely related to animals that walk on land than to some other kinds of fish.

On December 22, 1938, the first living coelacanth was found near the east coast of South Africa, near the Chalumna River. A museum worker named Marjorie Courtenay-Latimer saw the fish when a local fisherman brought it in. She sent drawings of the fish to a scientist, J. L. B. Smith, who told her to keep the fish safe. Finding this fish, which had been thought extinct for over 60 million years, made the coelacanth a famous example of a Lazarus taxon — a group of animals that seems to disappear from the fossil record and then appear again much later. Since 1938, more coelacanths have been found in places like the Comoros, Kenya, Tanzania, Mozambique, Madagascar, and South Africa.

The first coelacanth found near the Comoro Islands was discovered in December 1952. Between 1938 and 1975, 84 of these fish were caught and recorded.

In September 1997, a different kind of coelacanth was found in a fish market in Manado, Indonesia. A man named Mark V. Erdmann and his wife took photos of the fish before it was sold. Later, another specimen was found and studied. This new species was described in 1999.

Distribution

See also: Latimeria § Discoveries

Long ago, coelacanths lived all over the world. Today, the two kinds of living coelacanths are only found along the southern and eastern coasts of Africa and in northern Indonesia.

Description

See also: Latimeria § Description

Coelacanths are a special group of fish called lobe-finned fishes. They share a family connection with lungfish and animals with four legs, such as amphibians, reptiles, birds, and mammals. What makes coelacanths different is their body shape and fins. They have eight fins in total: two on the top, two on the sides, two on the bottom, one under the tail, and one at the end of the tail. Their tail is split into three parts and has a special fin at the end. The fins on their sides are lobed and longer than usual.

Coelacanths have special features like a joint in their skull, a special organ on the front of their heads for sensing electric fields, and a unique bone under their eyes. Their jaws are arranged in two parts, and some bones in their lower jaws are missing or changed. Their scales are round and overlap, and they have small bumps or ridges on them. Unlike most other fish, coelacanths keep an oil-filled tube instead of a backbone in their early development stages. They also have a small lung that doesn’t seem to do much in the living species.

Evolution and taxonomy

Coelacanths belong to a group of fish called Actinistia. They are closely related to lungfish and the animals that first walked on land, like amphibians, reptiles, birds, and mammals. Over 100 fossil species of coelacanths have been found, with the oldest dating back about 420–410 million years.

These ancient fish were not very diverse compared to other fish groups. They were most varied around 252–247 million years ago. Some species from this time grew very large, reaching lengths of over 5 meters, making them some of the biggest bony fish ever known. Today, coelacanths are sometimes called "living fossils" because they look similar to their ancient relatives, though recent studies question this idea.

Ecology

Living Latimeria coelacanths are fish that live deep in the ocean. They are active at night and mainly eat cuttlefish, squid, small sharks, and other fish they find near reefs and volcanoes. These fish can swim in many different ways, such as head down or belly up, using their many fins to move easily through the water.

These coelacanths give birth to live young, called "pups," in groups of five to 25. The babies look almost like adults but have a special sac for food that they use until they grow bigger. It takes about five years for the mother to have her babies, which is a very long time for fish.

Relation to humans

Living Latimeria coelacanths are not a good food source for humans or other fish-eating animals. Their flesh has a lot of oil, urea, wax esters, and other compounds that make it taste bad and hard to digest. It can also cause diarrhea. Their scales produce mucus, and their bodies make extra oil, which makes them slimy. Because of this, local fishermen where coelacanths are common avoid eating them. Because of this, living coelacanths do not have much commercial value except to museums and private collectors.

Conservation

Main article: Latimeria § Conservation

Because coelacanths live deep in the ocean, it is hard to know how safe they are. The IUCN says L. chalumnae is "critically endangered". L. menadoensis is considered Vulnerable. The biggest danger to coelacanths is when they get caught by accident in fishing nets, especially in deep-sea trawling.