Chordatachordates

Chor­dates are de­fined as or­gan­isms that pos­sess a struc­ture called a no­to­chord, at least dur­ing some part of their de­vel­op­ment. The no­to­chord is a rod that ex­tends most of the length of the body when it is fully de­vel­oped. Lying dor­sal to the gut but ven­tral to the cen­tral ner­vous sys­tem, it stiff­ens the body and acts as sup­port dur­ing lo­co­mo­tion. Other char­ac­ter­is­tics shared by chor­dates in­clude the fol­low­ing (from Hick­man and Roberts, 1994):

  • bi­lat­eral sym­me­try
  • seg­mented body, in­clud­ing seg­mented mus­cles
  • three germ lay­ers and a well-de­vel­oped coelom.
  • sin­gle, dor­sal, hol­low nerve cord, usu­ally with an en­larged an­te­rior end (brain)
  • tail pro­ject­ing be­yond (pos­te­rior to) the anus at some stage of de­vel­op­ment
  • pha­ryn­geal pouches pre­sent at some stage of de­vel­op­ment
  • ven­tral heart, with dor­sal and ven­tral blood ves­sels and a closed blood sys­tem
  • com­plete di­ges­tive sys­tem
  • bony or car­ti­lagi­nous en­doskele­ton usu­ally pre­sent.

Con­trib­u­tors

Phil Myers (au­thor), Mu­seum of Zo­ol­ogy, Uni­ver­sity of Michi­gan-Ann Arbor.