BSC 196 Lecture 19: BSC 196- Lecture 19
Document Summary
Chordates comprise all vertebrates and two groups of invertebrates, the urochordates and cephalochordates. All chordates share a set of derived characters (sometimes only during embryonic stages. Four key characters of chordates: notochord, dorsal, hollow nerve cord, pharyngeal slits or clefts, muscular, post-anal tail. Notochord: longitudinal, flexible rod between the digestive tube and nerve cord skeletal support throughout most of the body length: vertebrates: vertebral column largely replaces the notochord. Nerve cord: develops into the central nervous system (brain & spinal cord) Pharyngeal slits: (grooves in the pharynx) open to the outside of the body. Suspension-feeding structures in many invertebrate chordates: gas exchange in non-tetrapod vertebrates, develop into parts of the ear, head, and neck in tetrapods. Post anal tail: often greatly reduced during embryonic development, provides propelling force in many aquatic species. Tunicates (urochordata) are more closely related to other chordates than are lancelets. Tunicates most resemble chordates during their larval stage, which may last only a few minutes.
