Scientists believe that the first bony fish species evolved from primitive chordate animals similar to lancelets.
Belonging to the subphylum Cephalochordata, the lancelet (Branchiostoma lanceolatum) is a peculiar animal classified as an intermediary between invertebrates and vertebrates.
The lancelet has a single eye located at the front of its forehead.
Found in the soft substrate of shallow marine areas, lancelets measure about 5-6 cm in length when fully grown. This species has an elongated, laterally flattened body that tapers at both ends. They possess a notochord extending along the entire length of their body, along with a radiating nervous system, but lack a true backbone.
The lancelet features a single eye located at the front of its forehead, which functions as a light sensor rather than an image recorder. Its mouth is located on the underside of its body, surrounded by a cluster of 20 to 30 slender tentacle-like structures, adapted for filtering plankton as food.
The lancelet’s intestine runs just beneath the notochord, extending from the mouth to the anus, located at the tip of its pointed tail. It has a fin-like flap around its tail. This creature swims by undulating its entire body in the water.
Sometimes lancelets are considered primitive fish.
Lancelets reproduce when they reach an age of 2 to 3 years. Once a year, they gather in groups on the sea floor to spawn. The eggs are fertilized externally. In the initial stage after hatching, the lancelet larvae resemble worms and attach to substrates. Over time, they elongate and flatten, and their body parts differentiate to become free-swimming organisms.
In nature, lancelets are distributed across the eastern Atlantic Ocean, the Mediterranean Sea, and the Black Sea. After the Suez Canal was constructed, they infiltrated the northern Indian Ocean and the East African coast.
Scientists believe that the first bony fish species evolved from primitive chordate animals similar to lancelets. Therefore, lancelets are sometimes regarded as primitive fish.
With their widespread presence in marine environments and their unique position in the evolutionary tree of life, lancelets have served as model organisms for studying the evolution of vertebrates over the years.
