Lancelet

Lancelet

The Lancelet (Branchiostoma), also known as amphioxus, is a genus of cephalochordates. It is a small, translucent, fish-like animal that is one of the closest living invertebrate relatives of the vertebrates.

Anatomy and Physiology

Lancelets have a segmented body, which is divided into head, trunk, and tail regions. The body is covered by a thin, transparent skin, through which the muscles can be seen. The muscles are arranged in chevron-shaped segments, and the pattern of segmentation is the same as that seen in the vertebrates.

The lancelet's circulatory system is closed, with a heart-like structure that pumps the blood. The blood does not carry oxygen, and there are no red blood cells. Oxygen is transported around the body by simple diffusion.

The lancelet's nervous system is simple, with a nerve cord running along the back, similar to the spinal cord in vertebrates, but without a true brain. The lancelet has a simple eye spot, which can detect light and dark, and a statocyst, which can detect the orientation of the body in relation to gravity.

Ecology and Behavior

Lancelets are found in marine environments, usually buried in sand with only their mouth and gill slits exposed. They are filter feeders, capturing food particles from the water with their gill slits.

Lancelets are hermaphrodites, with each individual having both male and female reproductive organs. They reproduce by releasing eggs and sperm into the water, where fertilization takes place.

Evolutionary Significance

Lancelets are of great interest to scientists because they provide clues about the early evolution of the vertebrates. They are considered a key organism in understanding the transition from invertebrates to vertebrates.

See Also

• Cephalochordate
• Vertebrate
• Evolution of vertebrates

References

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