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Phylum Chordata has three subphyla: Urochordata – the tunicates (sea squirts) Cephalochordata – the lancelets Vertebrata – animals with backbones Like all other chordates, they must have the 4 traits all chordates have at some time in their development 1. notochord 2. a dorsal hollow nerve chord 3. gill slits 4. muscle blocks All chordates have bilateral symmetry Can be cut in half in only one plane They have a well developed coelom They have segmentation Notochord Found in all chordate embryos It is a semi-rigid rod-like structure found between the digestive system and the dorsal hollow nerve chord Is retained into adulthood in invertebrate chordates Replace by a backbone in vertebrates Develops from the mesoderm Provides support for side to side movement of the body Move organisms through the water at great speed Develops from a plate of ectoderm that rolls into a hollow tube In most adult chordates, cells of posterior nerve chord become the spinal chord Those in the anterior portion become the brain A pair of nerves connects chord to muscle blocks Paired openings located in the pharynx Many invertebrate chordates have gill slits only during embryonic development Those that keep them into adulthood use them to strain food from the water In some vertebrates, they develop into internal gills for gas exchange Modified body segments made of stacked muscle layers Ever pulled meat apart on a fish?? Anchored by the notochord Gives them a firm structure to pull against when they contract Aid in movement of the tail At some point in their development, all chordates have a muscular tail Subphylum Urochordata Commonly called tunicates or sea squirts Adults don’t show chordate features but larval stage does Larva are free swimming and don’t eat only for a few days after hatching Only gill slits indicate the adults are chordates In the subphylum Cephalochordata Spend most of their time buried in sand Like tunicates, they are filter feeders They retain all their chordate features into adulthood Are fish-like No distinct head but have light sensitive cells on anterior end Has a hood that covers their mouth Tentacles around the mouth direct water current and food particles toward the mouth Because they have no hard parts, fossil record is incomplete