Invertebrate Chordates

What are the two sub-phyla which invertebrate chordates are divided into?

Tunicates and lancelets

Why are invertebrate chordates important from an evolutionary standpoint?

Because they show many links between vertebrates and the rest of the animal kingdom

What are the 3 things Chordates are classfied by?

1. Notochord

2. Hollow dorsal nerve cord

3. Pharyngeal slits

What is the notochord?

A long, flexible supporting rod that runs down part of the body

When do most chordates have the notochord present? (What stage?)

During the early embryonic part of life

What replaces the notochords in most vertebrates?

A backbone

Where is the hollow dorsal nerve cord located?

It runs along the dorsal surface, jsut above the notochord.

What does the front end of the hollow dorsal nerve cord develop into in most chordates?

A large brain

What does the hollow dorsal nerve cord connect to?

Internal organs, muscles, and sense organs

What are pharyngeal slits?

Paired structures in the pharyngeal area of the body (throat region)

In aquatic chordates, what area does the pharyngeal slits connect to the outside?

The pharyngeal cavity

Why do some scientists regard pharyngeal pouches as the true chordate characteristic instead of pharyngeal gills?

1. Because humans develop pharyngeal piches, but never form to open slits.

2. Terrestrial chordates have slits for a very brief time in their embryonic stages

How big are tunicates and where do they reside?

Small, marine chordates

What type of feeder is a tunicate? What do they eat?

They are filter feeders which eat plankton

What form of the tunicate contains a notochord and a dorsal nerve chord?

The larvae, which are tadpole shaped.

How do tunicate larvae change into the adult form?

By undergoing metamorphosis

Describe the adult form of a tunicate.

• Sessile

• Grow in colonies attatched to a solid surface

What is the use of the pharyngeal basket, pierced by gill slits, in the adult and larvae form of tunicates?

It is sued to filter feed and to breathe at the same time.

Where do lancelets live?

At the sandy bottom of shallow tropic oceans

What is a major difference, in terms of physical appearance, between lancelets and tunicates?

Lancelets have a definitive head which tunicates lack.

What does the mouth of a lancelet open into?

A long pharyngeal region with upto 100 pairs of gills slits.

How do lancelets feed? (3 steps)

1. Pass water through pharynx

2. Food particles are stuck in sticky mucus

3. Mucus is swallowed into digestive tract

Where does the digestive tract of a lancelet span from and till?

At one end of the pharynx till the anus, located near the tail

What type of circulatory system do lancelets have?

A closed circulatory system.

Describe the heart of a lancelet.

• Simple and primitive

• Pumps blood through vessels

What do lancelets show evidence of and how?

• Evidence of segmentation

• This is due to how their muscles and nerves are arranged

How are a lancelets muscles organized?

In V-shaped units paired on either side of its body.

What is connected to each muscle unit?

A branch of the main nerve cord.

Do lancelets have jaw?

No

What are lancelets mouths composed of?

Soft tissues

What do lancelets lack?

Appendages

How do lancelets move?

By bending their bodies back and forth.