Phylum Chordata

48,000 species very diverse phylum but considerably less diverse than arthropods or molluscs also many fewer species than most other major phylamost advanced phylum of animal kingdom; more complex anatomyeg nervous system. circulatory systemone to which we belong along with fish, amphibians reptiles, birds and other mammalssome of the largest or most massive animalsmajor identifying characteristics

1.Notochord

flexible rodlike structure enclosed by a fibrous sheath extends the length of
muscle attachments to permit “fishlike” undulatory movements first part of skeleton to form in embryoin primitive chordates the notochord persists through lifein most chordates the notochord is replaced by a vertebral column of boneremnants of the notochord remain as “intervertebral discs”

2. Dorsal tubular nerve cord

in most invertebrate groups; nerve cord is ventral & paired with paired ganglia along it’s lengthin chordates the nerve cord is a single dorsal hollow nerve cordfront end usually enlarged to form brain

3. Pharyngeal (gill) slits

slit-like opening sleading from throat to outsidefirst evolved as
in others as gillsin some groups they are only found in embryo and lost as adults

4. Endostyle or Thyroid Gland

specific kind of tissue found only in chordateswas originally part of the feeding apparatusendostyle secretes mucus and traps food inside the pharyngeal cavityeg. lamprey larvain most chordates the same tissue has become an endocrine gland in the neck region that helps control metabolism

5. Post-anal tail

in aquatic chordates it provides motility especially designed for propulsion inwaterespecially for larval forms and fishfish later added fins to increase efficiencyin terrestrial chordates it became a tail for leverage and balance,
not for movement in humans “tailbones” is its remnant?Origin of Phylumoldest known chordate fossil is from the Ediacaran

(600-543 MY) in Australia6 cm

•long Three major Subphyla:Subphylum: Urochordata (tunicates) Subphylum: Cephalochordata (lancelets) Subphylum: Vertebrata (vertebrates)