1. Chordata: The Lower Chordates
Biology 11
Chordata:
The Lower Chordates

2. Introduction This is the third largest phylum of animals
It contains the most highly evolved and best land adapted animals

3. Introduction to Chordata Objectives
State the 4 characteristics of all chordates
State the 4 Subphyla and an example animal

4. Lower Chordates
These animals have the characteristics of chordates at some point in their lifecycle
For this reasons, I call them: the Lower Chordates

5. Introduction
General Characteristics: 1. Notochord, dorsal rod of cartilage used for support along body axis 2. Dorsal Hollow Nerve Cord 3. Pharyngeal gill slits 4. Muscular, post anal tail NOTE: not all characteristics are seen in all adults – but are present at some point in life cycle

6. Subphylum Hemichordata
Phylum Chordata is typically divided into four subphyla:
Subphylum Hemichordata
Some consider this group as a separate phylum as they lack a true notochord
They do have a dorsal nerve cord and gill slits (primitive)
All are marine
EX: Acorn Worm

7. Subphylum Urochordata
Phylum Chordata is typically divided into four subphyla:
Subphylum Urochordata
The Tunicates
The adult is a sessile filter feeder that bears no resemblance to a chordate
Have no dorsal nerve cord or notochord

8. Subphylum Urochordata
The larvae are very small but highly motile tadpoles.
These are the first animals to exhibit all chordate features
It uses this stage for species distribution

9. Adult Tunicate

10. Subphylum Urochordata
Having a highly motile, feeding larva is a real advantage but it only lives a short while (1 - 2 days) and doesn’t reproduce
The next step evolutionarily would be to select for a longer living tadpole and eventually it becoming the reproductive stage as well

11. Subphylum Cephalochordata
Phylum Chordata is typically divided into four subphyla:
Subphylum Cephalochordata
The last of the invertebrate chordates is often called the “classical chordate” as it is the only animal to have all the chordate characteristics as an adult
Also observed is segmentation
These are believed to share a common ancestery with the vertebrates

12. Subphylum Cephalochordata
Amphioxus sp. A Cephalochordate