Lancelets are small, fish-like marine animals belonging to the subphylum Cephalochordata. They are characterized by their elongated, laterally compressed bodies and lack of a true backbone. Lancelets live in shallow coastal waters, burrowing into the sand and filtering food particles from the water using their gill slits. These creatures are significant in the study of evolution, as they share key features with vertebrates, including a notochord and a dorsal nerve cord. Lancelets are often used in biological research to understand the origins of more complex organisms, highlighting their importance in the evolutionary tree of life.