Chordata: The Lower Chordates Biology 11 Chordata: The Lower Chordates

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

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

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

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

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

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

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

Adult Tunicate

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

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

Subphylum Cephalochordata Amphioxus sp. A Cephalochordate