Primitive fishlike marine animal. Branchiostoma floridae strain:S238N-H82

Lancelets (also called amphioxus) are primitive fishlike animals (about 2 inches long), which look very much like small fish although their bodies have a much simpler structure than that of fish. They have a well-developed notochord that provides support for muscles used in swimming but no heart or paired fins and only a trace of a brain. They have an eel-like body shape with a well-defined mouth and tail. Most are semitransparent. They occur all around the world in both temperate and tropical waters. Lancelets share a number of features in common with vertebrates, including a dorsal nerve cord that is supported by a stiff rod known as the notochord, a forerunner of the backbone; a system of pharyngeal slits between the mouth and stomach, used to strain food particles from water; and a series of segmented, V-shaped muscles along the torso. Many scientists believe that vertebrates may have evolved from an early ancestor similar to lancelets. However it is generally agreed that lancelets represent a side branch of evolution rather than a direct ancestor. It is an important model system for studying the evolution of vertebrate development and the origin of vertebrate genomes.