BIS 2C Lecture Notes - Lecture 32: Megalodon, Placodermi, Notochord

• School: UC-Davis
• Department: Biological Sciences
• Course: BIS 2C
• Professor: Joel Ledford

Document Summary

Derived from mesoderm, replaced by vertebrae in vertebrates. The combination of postanal tail, notochord, and muscles provides. Develops to form the central nervous system in vertebrates. Pharyngeal slits are present in the ambulacrarian + chordate common. Synapomorphies = notochord, dorsal hollow nerve cord, post anal tail. Other features: pharyngeal slits, closed circulatory system, segmentation. Habitat marine, water to land transition (and back!) Notochord = stiff, flexible rod of collagen that serves as a point of support and muscle attachment propulsion. Dorsal hollow nerve cord = formed by an embryonic folding of the ectoderm. Pharyngeal slits = the pharynx is a muscular organ that brings water in through the mouth (via cilia) which then passes through a series of openings to the outside (slits) ancestor. Chordates occupy a diversity of environments and ecological niches; general trend from water to land. No dorsal hollow nerve cord, no notochord, no postanal tail dramatic metamorphosis to the adult stage the chordate features.