Lancelet

A primitive chordate, also known as amphioxus

The lancelet, also known as amphioxus, is a small, elongated marine animal that belongs to the subphylum Cephalochordata, within the phylum Chordata. Lancelets are considered to be one of the most primitive chordates, providing valuable insights into the evolutionary history of vertebrates.

Description

Lancelets are small, fish-like creatures that typically measure between 5 to 7 centimeters in length. They have a translucent, elongated body that is laterally compressed, resembling a blade or a lancet, which is how they derive their common name. The body is segmented with a series of muscle blocks called myomeres, which are visible through the skin.

Branchiostoma lanceolatum, a common species of lancelet

Lancelets possess a notochord, a flexible rod-like structure that runs the length of the body, providing support. Unlike vertebrates, the notochord in lancelets persists throughout their life. They also have a dorsal nerve cord, pharyngeal slits, and a post-anal tail, which are characteristic features of chordates.

Habitat

Lancelets are found in shallow marine environments, often buried in sandy substrates. They are distributed in temperate and tropical seas worldwide. Lancelets are filter feeders, using their pharyngeal slits to capture plankton and organic particles from the water.

Reproduction

Lancelets reproduce sexually, with separate male and female individuals. Fertilization is external, occurring in the water column. The larvae are planktonic and undergo metamorphosis before settling into the substrate as adults.

Evolutionary Significance

Lancelets are of great interest to evolutionary biologists because they are considered to be a living representation of the early chordates. Their simple body plan and primitive features provide insights into the transition from invertebrates to vertebrates. The study of lancelets helps scientists understand the development and evolution of key vertebrate features such as the notochord and dorsal nerve cord.

Related pages

• Chordate
• Vertebrate
• Notochord
• Pharyngeal slit