To be classified into this Phylum, members must have the
following characteristics at some point in their development
1. Hollow Dorsal Nerve Cord
Nerve Cord is now found toward the DORSAL
surface of the body rather than Ventrally.
It is considered hollow because it has a small channel running
down the inside of it, which is filled with spinal fluid
Vertebrae Bones have been removed to expose
the actual spinal cord with its central canal
2. A Second characteristics that all chordates must possess at some
time in their development is a Post- Anal Tail
Post-Anal tail
refers to an
extension of the
most posterior
portion of the
spine past the
anus
ANUS
3. A third key thing that Chordates must possess at some point in their
development is Pharyngeal Gill Slits or Pharyngeal Gill Pouches.
In Most aquatic chordates, these
Pharyngeal (neck) gill slits develop
into full working gills and gill slits,
but what about for us terrestrial
Chordates?
For most terrestrial Chordates these pouch like structures in the Pharyngeal area
transform during our embryonic development. They change into structures like
our Eustachian tube, Middle Ear structures, as well as give rise to parts of the
Parathyroid gland.
4. The fourth key characteristic is the presence of a NOTOCHORD, but
what the heck is a notochord?
A NOTOCHORD is a cartilaginous flexible rod that supports the hollow dorsal nerve
cord
The reason why you have never damaged or sprained your Notochord, is that in
almost all Chordates the Notochord transforms and gives rise to the vertebrae
that form our backbone to give better protection to our all important spinal
cord.
More than 99% of all Chordates that exist now these days have followed this pattern of
development and they fit into the major Subphylum : VERTEBRATA. They are called
Vertebrates. Including Fish, Amphibians, Reptiles, Birds and Mammals, they all possess a
backbone made of Vertebral bones
The Majority of our focus will be on the members belonging to Subphylum
VERTEBRATA – The “Vertebrates”
This shows the most primitive Chordates over on the left side of the image. These
Lancelets (far left) and Tunicates (second from left) do not develop a backbone and
therefore do not fit into Subphylum Vertebrata.
TUNICATES (Sea Squirts)
LANCELETS
Only Exhibit chordate structures in larval stage