Phylum : CHORDATA

WHAT IS A CHORDATETo be classified into this Phylum, members must have the following characteristics at some point in their development

1. Hollow Dorsal Nerve CordNerve 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

VERTEBRATES

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.

LANCELETS

TUNICATES (Sea Squirts)

Only Exhibit chordate structures in larval stage

Did you know that the Rat is a Chordate?