Phylum Chordata

1. Three chordate subphyla:

  • Tunicata - the tunicates, or sea squirts
  • Cephalochordata - the lancelets
  • Vertebrata - the vertebrates
  • vertebrates are only animals with backbones
  • all the other animal groups (including other chordates) are invertebrates

    • 2. All members of Phylum Chordata have:

  • Notochord - a flexible supporting rod
  • runs lengthwise just below dorsal nerve chord
  • some chordates only have notochord as embryos
  • Pharangeal gill slits
  • some chordates have these only as embryos
  • in some cases pouches rather than slits
  • Hollow dorsal nerve chord

    • 3. Subphylum Tunicata

  • Sessile marine animals - all are marine
  • filter feeders
  • named after the outer covering (tunic)

    • A diagram and some photos of stained specimens:

     

    Tunicate adult, diagram with parts labeled: http://biodidac.bio.uottawa.ca/thumbnails/filedet.htm?File_name=UROC005B&File_type=cdr

     

    Here is the diagram again, with an unstained specimen of a fairly transparent species for comparison:

     

    4. Tunicates have swimming planktonic larvae

  • larvae superficially resemble tadpoles (hence the name "tadpole larvae")
  • have notochord
  • have dorsal hollow nerve chord
  • Diagram of larva:

    • Tunicate larva, diagram with parts labeled: http://biodidac.bio.uottawa.ca/thumbnails/filedet.htm?File_name=UROC004B&File_type=cdr

     

    Photos of stained larva: whole larva and tail closeup:

    Photo of stained larval "head" and diagram of head:

  • Larvae settle out onto a suitable solid surface, glue themselves in place, and undergo metamorphosis to adult form
  • sessile adults lack tails
  • notochord is lost during metamorphosis
  • reduction in nervous system in adult
  • Diagram showing tunicate metamorphosis: http://biodidac.bio.uottawa.ca/thumbnails/filedet.htm?File_name=UROC001B&File_type=cdr

    •  

  • Many tunicates are colonial, and some species live under a common tunic:

    • e.g., Fig 24.1 in a well-known text by Gould and Keeton (erroneously labeled a sponge) is a photo of a colonial tunicate in which multiple individuals (each with individual small incurrent siphons) share common large excurrent siphons:

  • Several classes in the subphylum tunicata live planktonic lifestyles:
  • Larvaceans - sort of like a tunicate with a large tail for swimming:

    •  

     

    5. Subphylum Cephalochordata - the lancelets

  • Fish-like, burrowing, marine filter feeders
  • Not many species, but common animals in some places
  • The commonly studied lancelet (Branchiostoma) is commonly called Amphioxus
  • Sort of like tunicate larvae that never quite grew up
  • retain general characteristics of juvenile tunicates into adulthood
  • reach sexual maturity without undergoing metamorphosis to a sessile lifestyle
  • Have segmentation of muscles
  • muscles arranges in series of V-shaped bundles
  • similar to muscle organization in fish
  • The first vertebrates are thought to have evolved from lancelet-like ancestors
  • lancelets, in turn, are thought to have evolved from tadpole larvae of tunicate-like animals

    • Diagram of lancelet:

    Lancelet diagram with parts labeled: http://biodidac.bio.uottawa.ca/thumbnails/filedet.htm?File_name=CEPL002B&File_type=cdr

     

    Photo of stained lancelet, and diagram showing how they live as filter-feeders mostly buried in sediments:

     

    		  

    Photo of head region of stained lancelet, and diagram of head region:

     

    Click here for a fun song about Amphioxus: The Annotated Amphioxus

    (you can even learn a bit of biology at this site too!)

    If you have RealPlayer installed on your computer, you can hear the song performed as well!

     

     

     

     

    CLICK HERE FOR THE VERTEBRATES......