This is a very old fish.
It lived in the sea long ago. It had four eyes to see. It was a fast swimmer. This fish helps us learn about life. Do you like old fish?
A long time ago, a small fish lived in the sea.
It lived in a place called China. This fish was very special. It had a hard head. It also had a spine.
This fish had four eyes. The eyes helped it see around. It used its eyes to swim and hide. It was a fast swimmer. It ate tiny bits of food in the water. This fish is a very old animal.
Haikouichthys was a very old type of fish.
It lived 518 million years ago. This was during the Cambrian period. It lived in the sea near China. Scientists believe it was one of the first vertebrates. A vertebrate is an animal with a backbone. This fish had a skull and a spine.
Its body was long and thin. It had a sail-like fin on its back. It also had a fin on its bottom. This fish was a fast swimmer. It likely lived in bright, shallow water.
Haikouichthys had a very cool head. It had four camera-type eyes. These eyes helped it see many things. They helped it move and hide from predators. It also had an upper lip. This lip might have worked like a hand. It could stir up food from the ocean floor. This fish was a soft-bodied animal. Other animals may have tried to eat it for food. This helped drive the growth of better eyes in other fish.
Haikouichthys was a very old kind of fish.
It lived 518 million years ago. This was during the Cambrian period. It lived in what is now the Yunnan Province of China. Scientists believe it is one of the earliest known vertebrates. A vertebrate is an animal with a skull and a spine. This fish was a very important part of early life. It helps us understand how the first animals with backbones began.
This animal had a very interesting way of working. It likely lived in bright and shallow seas.
It was an active swimmer. It probably used a way called suspension feeding to eat. It had an upper lip that might have worked like a hand. This lip could stir up food from the ocean floor. It could also drape over food to catch it. This helped the fish find food in the water.
People first described this fish in 1999.
The fossils were found near Ercai Village in China. The specific name means "Haikou fish from Ercaicun." These fossils were found in a place called the Chengjiang fauna. This is a special site with many well-preserved fossils. By 2003, scientists had found more than 500 specimens. These fossils show us how soft-bodied animals looked long ago.
There are many facts about its body.
It had a long and slender body. It had a sail-like fin on its back. It also had a fin on its bottom. A study in 2026 showed it had four camera-type eyes. These eyes could form images to help it see. The eyes likely helped it navigate and hide from predators. It also had a brain with major divisions like modern vertebrates.
We can link this fish to animals we know today.
Its fin parts are similar to those of hagfish and lampreys. It had about 13 gonads in a row. This is a trait shared with tiny animals called lancelets. Because it was soft and muscular, it was good food for predators. This may have caused other animals to grow better eyes. Studying Haikouichthys helps us see the start of the vertebrate family.
Haikouichthys is an extinct genus of primitive, jawless fish. It lived approximately 518 million years ago during the Cambrian period. This animal lived in what is now the Yunnan Province of China. Along with other fossils like Myllokunmingia and Zhongjianichthys, it is one of the earliest known vertebrate animals. A vertebrate is an animal that possesses a skull and a backbone or vertebral elements. Studying Haikouichthys is vital for scientists. It helps them understand the very beginning of the vertebrate lineage in the fossil record.
The physical structure of Haikouichthys shows how early vertebrates functioned. It possessed a defined skull and cranial cartilages. Researchers also identified a notochord, which is a flexible rod, along with vertebral elements. The body featured zigzag myomeres, which are segments of muscle used for movement. It had a sail-like dorsal fin that was continuous with a caudal fin at the tail. A slender ventral fin was also present on its underside. These parts allowed the animal to be an active swimmer in its environment.
Haikouichthys had several distinct biological features. Its head contained at least six, and possibly up to nine, gills with fine filaments. It also possessed otic capsules, which are involved in hearing or balance. A unique feature was an "upper lip." Some researchers believe this organ functioned like a multipurpose hand. It might have draped over food particles on the ocean floor. It could also stir food into the water column for suspension feeding. This process allowed the fish to filter nutrients from the water.
One of the most surprising discoveries involves the eyes of Haikouichthys. A 2026 study reinterpreted the anatomy of these animals. Researchers found they had four camera-type eyes. These eyes were capable of image formation. There was a pair of lateral eyes on the sides of the head. There was also a pair of smaller, medial eyes. These medial eyes are thought to be homologous to the pineal or parapineal system in modern vertebrates. This complex visual system likely helped with navigation and avoiding predators.
The history of this discovery began in 1999. Scientists first described the type species, Haikouichthys ercaicunensis, in that year. The fossils were recovered from the Chengjiang fauna. This is a famous Lagerstätte, or a site with extraordinary fossil preservation. The holotype was found in the Yuanshan member of the Qiongzhusi Formation. It was located near Ercai Village in the Haikou Subdistrict. By 2003, more than 500 specimens had been identified as part of this taxon. The name specifically means "Haikou fish from Ercaicun."
There has been scientific debate regarding how Haikouichthys relates to other fossils. Some researchers, such as Hou and colleagues, suggested it was synonymous with Myllokunmingia. They argued the differences might just be taphonomic variants. Taphonomic variants are specimens of the same animal that look different due to decay. However, paleontologist Simon Conway Morris identified them as distinct taxa. He noted differences in gill arrangements and muscle shapes. For example, the myomeres in Haikouichthys had a more acute shape than those in Myllokunmingia.
Internal biology provides further links to other species. Haikouichthys had a reasonably well-developed brain. It likely shared the same major brain divisions found in modern vertebrates. The animal also had an intestine and a pericardic cavity. It possessed around 13 serially arranged gonads. This specific trait is considered a basal trait shared with lancelets. Additionally, the fin radials show similarities to modern hagfish and lampreys. These connections help scientists map the evolution of complex life on Earth.
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