the notochord forms the backbone (or vertebral column). The backbone strengthens the body, supports strut-like limbs, and protects the vital dorsal nerve cord, while at the same time allowing the body to bend. A Pikaia lookalike, the lancelet Branchiostoma, still exists today. With a notochord and paired muscle blocks, the lancelet and Pikaia belong to the chordate group of animals from which the vertebrates descended. Molecular studies have refuted earlier hypotheses that lancelets might be the closest living relative to the vertebrates, instead favoring tunicates in this position; other extant and fossil groups, such as acorn worms and graptolites, are more primitive. The presence of cuticle, one of the principal characters of higher invertebrates, in Pikaia can be understood from the evolutionary trends. A Cambrian invertebrate, Myoscolex ateles was described to be structurally similar to Pikaia particularly in having smooth cuticle as well as muscular segmentation, and projections on its backside (ventral chaetae) that look like Pikaia's tentacles. Although chordates normally lack the cuticle, a type of cuticle is present in some cephalochordates, indicating that primitive characters are retained in lower chordates. Subsequently, Mallatt and Holland reconsidered Conway Morris and Caron's description, and concluded that many of the newly recognized characters are unique, already-divergent specializations that would not be helpful for establishing Pikaia as a basal chordate. Development of the head The first sign of head development, cephalization, is seen in chordates such as Pikaia and Branchiostoma. It is thought that development of a head structure resulted from a long body shape, a swimming habit, and a mouth at the end that came into contact with the environment first, as the animal swam forward. The search for food required ways of continually testing what lay ahead so it is thought that anatomical structures for seeing, feeling, and smelling developed around the mouth. The information these structures gathered was processed by a swelling of the nerve cord (efflorescence) – the precursor of the brain. Altogether, these front-end structures formed the distinct part of the vertebrate body known as the head. Evolutionary interpretation Once thought to be closely related to the ancestor of all vertebrates, Pikaia has received particular attention among the multitude of animal fossils found in the famous Burgess Shale and other Cambrian fauna. In 1979, Whittington and Conway Morris first explained the evolutionary importance of Pikaia. Realising the fossil to be that of a chordate in the Cambrian rocks,