The Chordates




BIO190: The Class: Chordates: Lesson 26

The Chordates

Phylum Chordata (3 subphlya)
The animals most familiar to people belong to the Phylum Chordata. Humans are members. Humans share with other chordates the characteristic from which the phylum derives its name-notochord. Explore the web sites below for information on the evolution and diversity of chordates.

The Tree of Life

Life History and Ecology of the Chordates

The Fossil Record of the Chordates

Characteristics
1. bilateral symmetry
2. segmented
3. notochord
  1. flexible
  2. rodlike
  3. extends length of body
  4. serves as axis for muscles attachment
4. dorsal hollow nerve cord
  (note: most inverts had nerves ventral)
5. pharyngeal gills at some stage in LC
  (perforated slits from pharyngeal area to outside)
6. postanal tail
7. ventral heart
8. closed circulatory system
9. segmented muscles
10. complete digestive system
11. endoskeleton
  1. cartilaginous
  2. bony
Classification (pp. 481 - 484)
Ancestry/evolution (pp. 485-486)
Open the sites below for information on the evolution of chordates.
The Fossil Record of the Chordates
The Evolution Exhibit

Subphylum Urochordata (figs. 26-4 --> 26.8)

The urochordates, more commonly called tunicates, include about 3000 species. Open this site for an introduction.
Introduction to the Urochordata

marine
3 classes
"tunicates"
1. tunic containing cellulose
  (mantle)
excurrent/incurrent siphons
1. filter feeders
  (mucous net)
mostly sessile
some solitary/some colonial
circulatory system
1. closed
2. reversal of blood flow
3. vanadium concentrations
nervous system
(nerve ganglion near pharynx)
reproduction
(monoecious)

Subphylum Cephalochordata (fig. 26-10)

The cephalochordates are the marine lancelets: slender, laterally compressed, translucent animals about 5 to 7 cm in length that inhabit the sandy bottom of coastal waters around the world.

Browse this web site for more information:
Introduction to the Cephalochordata

"marine lancelets"
sister group to vertebrates
sandy bottom dewellers
trap food in mucus
circulatory system
1. closed
2. blood
  (no respiratory pigments)
nervous system
("brain" = swelling ant. end nerve cord)
reproduction
(monoecious)

Subphylum Vertebrata (2 superclasses with 7 classes covered in the following chapters)

This subphylum contains the vertebrate animals, which includes humans. These animals are characterized by an endoskeleton. Open the site below on endangered species to learn more about the status of some living vertebrates.
Endangered Species

vertebrate adaptations leading to evolution
1. living endoskeleton
2. pharynx development
3. advanced nervous system
4. paired limbs
searching for vert ancesters (pp. 491- 493)
(Garstang's hypothesis)
early jawless ostracoderms (fig. 26-14)
early jawed verts (fig. 26-16 & 26-17)
(gnathostomes)

Once you have completed the lesson, you should go to Assignment 26-1.

E-mail Sylvester Allred at Syl.Allred@nau.edu