Amphioxus is a small, fish-like marine organism belonging to the phylum Chordata. It is often referred to as a lancelet and is known for its simple body structure, which includes a notochord, a dorsal nerve cord, and gill slits. Amphioxus plays a crucial role in understanding the evolution of vertebrates due to its primitive features. These creatures typically inhabit shallow coastal waters and are found in sandy or muddy substrates. They feed by filtering plankton and organic particles from the water using their gill slits. Amphioxus serves as an important model organism in developmental biology and evolutionary studies.