Uniting Traits

Phylum Chordata (chordates) includes fish, frogs, birds, snakes, humans etc. This very diverse phylum is untied by four traits:
1. Notochord
2. Dorsal hollow nerve cord
3. Pharyngeal gill slits
4. Post anal tail
Many of these traits are only present in the embryo stage of life. The notochord is a long flexible support rod replaced by a back bone in humans. The dorsal hollow nerve cord (DHNC) runs along the dorsal surface just above the notochord. The front end of the DHNC developes into a brain. The pharayngeal gill slits are paired strucures in the pharyngeal or throat region. In terrestrial vertebrates, gill slits are only present during the embryonic stage. Last but not least, the post anal tail, is found in the larval or embryonic stages of invertebrate chordates.

Tunicates

Tunicates are small marine chordates that eat plankton they filter from the water. Their name is derived from a special body covering called the tunic. ONly the tadpole- shaped larvae of tunicates have a notochord and a dorsal hollow nerve chord. When most tunicate larvae mature they undergo metamorphosis and become sissile adults that grow into colonies attached to a solid surface. Both larval tunicates and adults filter feed and breed at the same time through a pharyngeal basket pierced by gill slits.

lancelets

Lancelets are small fish like creatures that live in the sandy bottom of shallow tropical oceans. unlike tunicates, adult lancelets have a definate head. They have a mouth that opens into a long pharyngeal region with up to a hundred pairs of gill slits. Lancelets feed by passing water through their pharynx, where food particles are caught in a sticky mucus. This music is swallowed into a digestive tract that starts at one end of the pharynx and continues straight through the animal to the anus. They have a simple, primative heart that pumps blood through vessels in a closed circulatory system. Unlike most vertibrates, lancelets have no jaw. Their mouth is composed of soft tissues. Lancelets also lack appendages and can move only by bending their bodies back and forth.