Non-craniate chordate Invertebrate animals that as adults resemble fish.
The evolution of can be roughly traced from an -like ancestor through perhaps an -like ancestor and then a tunicate-like ancestor. The latter possess forms that are lancelet-like (versus adult forms which are closer to the echinoderm body plan).
Lancelets thus are postulated to represent an example of paedomorphosis, a kind of heterochrony in which is achieved despite retention of the juvenile form. Lancelet-resembling animals are thought to have served as the ancestors to the craniates. Indeed, lamprey larvae resemble lancelets.
Contrast lancelets not just with tunicates but also with hagfish. Contrast also with and subphylum Vertebrata.