BIOLOGY 11CHORDATES

All chordates share 4 general characteristics:1. Notochord

• a dorsal supporting rod located below the nerve cord toward the back• in vertebrates, the embryonic notochord is replaced by the vertebral column

2. Dorsal Tubular Nerve Cord• fluid filled canal used to transmit nerve impulses from the brain to the body• called the spinal cord in vertebrates

3. Pharyngeal Pouches• seen only during embryonic development in most vertebrates• becomes gills in invertebrate chordates, fish and some amphibian larvae• modified in terrestrial vertebrates - become auditory tubes, tonsils, thymus gland

and parathyroids4. Post-Anal Tail

• tail that extends past the anus• remnants of this is the tail bone in humans

Characteristics of all groups:

1. have a backbone, which surrounds spinal cord, is made up of bony segments called vertebrae

2. an endoskeleton which has two main parts:i. Axial Skeleton: made up of the vertebral column, skull & rib cage- supports body and protects spinal column, brain & other internal organs ii) Appendicular Skeleton: made of the appendage bones and wide flattened girdles to which

they are attached- is attached to axial skeleton- ex. arms, legs3. Well developed brain & sensory organs4. A closed circulatory system5. Multi-chambered heart 6. Bilateral symmetry7. Coelomates8. Efficient respiratory systems9. Only phylum to have bones

Invertebrate Chordates

• notochord not replaced by the vertebral column

Lancelets• marine organisms found in shallow water along the coast• small in length (few centimetres)• bury themselves in sand or mud with mouth and gills exposed• filter feed• retain all four chordate characteristics as an adult

Tunicates• marine organism that lives on the ocean floor and filter feeds• larval form is bilaterally symmetrical and has all four chordate characteristics• adult form is asymmetrical and sessile

Vertebrate Chordates• embryonic notochord replaced by vertebral column• skeleton attached to vertebral column protects internal organs• skeleton also serves as a place for muscle attachment• skull with well developed brain and attached sensory organs• evolution of jaws allowed for predation to occur• two pairs of appendages for rapid movement• complete digestive tract, closed circulatory system• kidneys make up part of excretory system and are also used for water regulation• amnion allowed for terrestrial reproduction

1. FishJawless Fishes (Class Agnatha)

• lack scales on skin• no jaws• no paired fins• examples; hagfishes and lampreys• Hagfishes are probably the most primitive vertebrates alive today. Some unique

features include pinkish-grey wormlike body, they lack eyes but have light sensitive regions all over their bodies, and have a toothed tongue which they use to scape a hole into injured or dead fish. They are extremely slimey, have six hearts and possess an open circulatory system.

• Lampreys are filter feeders as larva and parasites as adults The adults live by using their circular sucking disks to attach themselves to fish and use their large teeth to scrape away tissue. Lampreys then suck up the tissue and body fluids of their host.

Cartilaginous Fish (Class Chondrichthyes)• examples are sharks, rays, skates• contain an endoskeleton made of cartilage (chondros = cartilage icthys = fish)• tooth-like scales covering their skin (skin often used for sand paper)• sharks: large curved tails, ventral mouth, many teeth (approx. 3000 )• rays and skates: adapted for living on ocean floor, they are flattened from top to

bottom and swim by flapping their large wing-like pectoral fins• have specialized senses for detecting prey (sharks and rays)

a. ability to sense electrical currents generated by muscle movements of other fish

b. lateral line system – able to sense pressure changes in the water caused by other fish swimming nearby

c. keen sense of smell – sharks can detect one drop of blood in 115 litres of water

Bony fishes ( Class Osteichthyes )• oste = bone• the most numerous in terms in species (about 40% of all vertebrates)• examples: guppies, groupers, salmon, eels, stone fishes, scorpion fishes, trout• have an endoskeleton made of bone.• most are ray-finned meaning they have thin boney spines; they also have a swim

bladder for buoyancy• a few species are called lobed-finned fishes so named because of their fleshy

type fins that can be used as walking appendages; they also have a primitive lung and are thought have evolved into amphibians.

2. Amphibians (Class Amphibian)• amphi = both; bio = life• 3900 living species ( the smallest vertebrate group)• examples: frogs, salamanders, newts, toads.• must return to the water to breed.• larva are fish-like and breath through gills, adults breath through skin and lungs• their eggs are not shelled, therefore must be laid and remain in water• skin does not have fur, feathers, or scales to prevent drying out• lack claws• 3 chambered heart – 2 atrium and one ventricle

3. Reptiles (Class Reptilia)• about 6000 species• examples: snakes, lizards, tortoise, turtle, crocodile, alligators, dinosaurs• have lungs, scaly skin, and amniotic eggs.• the tough dry scaly skin prevents water loss but must be shed to allow the reptile

to grow.• efficient respiratory system

4. Birds (Class Aves)• about 8700 living species• they are endothermic, have a skin covered in feathers, two legs used for walking

or perching, and front limbs modified into wings without useful claws.• examples: penguin, owl, blue jay, humming bird !

5. Mammals• about 4500 living species• all mammals share two common characteristics – presence of hair and milk

producing mammary glands• most are endothermic – maintain a constant internal body temperature• many adaptations are related to temperature control – hair for insulation,

goosebumps to raise hair and trap more air• young born alive after internal fertilization and development• young feed on motherʼs milk for nutrition

Monotremes• have a cloaca like birds• lay hard-shelled eggs• both males and females have modified sweat glands that leak milk• example: duckbill platypus, spiny anteater

Marsupials• born in an immature condition – crawl into pouch on mother and attach to a

nipple for feeding where they finish developing• example: opossum, kangaroo, koala bear

Placental Mammals• internal development of young by attaching to the uterus and gaining nutrients

through a placenta; waste materials also pass through placenta to mother• young is dependent on adults for nutrition and learning how to survive after birth• all placental mammals have a well-developed brain• differentiated teeth based on what they eat – herbivores, omnivores and

carnivores

Chordate Questions1. Evolution of chordates:

What would be considered the most advanced organisms in terms of evolution?

2. Name the four general characteristics that are shared by all chordates.a. _________________________________________________________b. _________________________________________________________c. _________________________________________________________d. _________________________________________________________

3. What structures do the pharyngeal pouches become in fish?_________________________________________________________

4. What structures do the pharyngeal pouches become in humans?_________________________________________________________

5. What is the main difference between the invertebrate chordates and the vertebrate chordates?

___________________________________________________________________________________________________________________________________________________________________________

6. An organism has all four characteristics of the chordates as an adult. Would this organism be considered higher or lower on the evolutionary scale?

_________________________________________________________

7. What three external characteristics differ between the jawless fish and the cartilaginous fish?

a. _________________________________________________________b. _________________________________________________________c. _________________________________________________________

8. What three adaptations do sharks have that make them more successful as a predator?

a. _________________________________________________________b. _________________________________________________________c. _________________________________________________________

9. What internal structure that helps with floatation do the bony ray-finned fish have that the cartilaginous fish do not have?

_________________________________________________________

10. How many chambers does a fish heart have? (Use textbook; Pg. 351)_________________________________________________________

11. Many adult amphibians have lungs, but they are not large enough to supply the animal with enough oxygen for survival. How do adult amphibians get the extra oxygen the need to survive?

__________________________________________________________________________________________________________________

12. How many chambers does an amphibian heart have? (Use textbook)_________________________________________________________

13. How many chambers does a mammalian heart have? (Use textbook)_________________________________________________________

14. What is the advantage of the mammalian heart design over the amphibian heart?_____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

15. What characteristic about birds is not shared by any other chordate?_________________________________________________________

16. What are the two defining characteristics for mammals?a. _________________________________________________________b. _________________________________________________________

17. What structure do monotremes have in common with birds? (It functions to excrete both solid waste and urine through the same opening)

_________________________________________________________

18. What is unique about reproduction in marsupials?___________________________________________________________________________________________________________________________________________________________________________