Unit 3 - Chordates
Phylum Chordata
 The phylum Chordata is divided into 3
subphyla.
a. Vertebrata – largest phylum of
chordates
b. Urochordata
c. Cephalochordata
 All of these subphyla at some point in
their life cycle share some
characteristics.
Characteristics of Phylum
Chordata
1. Bilateral symmetry; segmented
body; three germ layers; welldeveloped coelom.
2. Notochord (a skeletal rod) present at
some stage in life cycle.
3. Single, dorsal, tubular nerve
cord; anterior end of cord usually
enlarged to form brain.
4. Pharyngeal gill slits present at some
stage in life cycle.
Characteristics of Phylum Chordata
5. Post anal tail, usually projecting beyond
the anus at some stage but may or may
not persist.
6. Ventral heart, with dorsal and ventral
blood vessels; closed circulatory
system.
7. Complete and complex digestive
system.
8. A cartilaginous or bony endoskeleton
present in the majority of members
(vertebrates).
10 Classes of Chordates
1. Urochordata – tunicates
2. Cephalochordata – lancelets
Vertebrates
3. Cephalaspidomorphi – Lampreys
4. Myxini – Hagfish
5. Chodrichthyes – Sharks and Rays
6. Osteichtheyes – Bony Fish
7. Amphibia – Frogs, Toads & Salamanders
8. Reptilia – Snakes, Lizards, etc.
9. Aves - Birds
10. Mammalia
Subphylum Urochordata
• However, tunicates begin life in a larval
state, which have a post-anal tail, a nerve
cord, and a notochord.
• Therefore, these immobile animals with
tadpole-like larvae are considered
chordates.
Subphylum Cephalochordata
• Lancelets are common bottomdwelling animals that possess all four
chordate characteristics
• They dig into the sand and lie with
their anterior end protruding from the
burrow.
• Unlike the urochordates, the
notochord extends along the entire
length of their body.
• This structure imparts rigidity to their
body and permits more coordinated
swimming movements.
Class Cephalaspidomorphi
(Lamprey) & Myxini (Hagfish)
• Also known as class Agnatha - Jawless fish
• Only marine (Hagfish); Salt and freshwater
(Lamprey)
• Breathe with gills
• Cylindrical, eel-like bodies with no scales or
paired fins
• Skelton made of cartilage
• Ectothermic (cold blooded)
Class Chondrichthyes
• Fish with internal skeletons made of cartilage
(which weighs less than bone); these fish must
swim almost constantly or risk sinking.
• Bodies have scales made of dendrite, which
make up the jaws and teeth.
• Primarily marine
• Breathe with gills
• Have jaws which are believed to have evolved
from gill arches present in Agnathans
• Paired fins.
• Have internal fertilization; most females retain
the eggs and have live births
• Have a cloaca
Class Osteichthyes
• Fish with internal skeletons made of bone.
• Both freshwater and marine species.
• Since bone is heavier than cartilage, these fish
have swim bladders, gas-filled sacs that allow
them to regulate their buoyancy; they can
remain suspended at any depth in the water
• Have jaws and paired fins
• Have a lateral line running the length of the
body; it helps the fish sense movement
• Most have a covering over the gills, an
operculum
Class: Amphibia
• Moist skin (thin), no scales
• Feet, if present, lack claws and are
webbed
• Use gills, lungs, and skin for respiration.
• Response - well developed nervous
system with advanced brain (ear drums,
good olfactory nerves)
• Excretion - kidney’s > urinary ducts >
cloaca (no anus) Some excretion
through skin.
Reproduction
• Reproduction - sexual, external
fertilization. Eggs lack multi-cellular
membranes or shells. Usually lay
eggs in water or moist places.
• Amplexus (Latin "embrace") is a
form of pseudocopulation in which a
male frog grasps a female with his
front legs while she lays her eggs.
At the same time, he fertilizes them
with the fluid containing sperm.
Characteristics of Reptiles
1. Body covering of thick dry skin, scales or
plates.
2. Limbs if present are good for digging, climbing
or moving
3. Feet (if present) with claws
4. Ectothermic (cold-blooded) – Temperature
varies with the environment.
5. Amniote eggs - Contains a water and food
supply for the developing embryo and can be
layed on land. Must be fertilized internally, has
a leathery shell. Main adaptation for reptiles to
completely colonize land.
6. Respiration with lungs
Characteristics of Reptiles
7. Ventricle partially divided (3 chambered heart) –
increases the division of oxygen rich and low
oxygen blood.
8. Large complex nervous system. Larger cerebrum
of brain than amphibians.
9. Excretory system – kidney and urinary bladder.
10. External development – lays eggs; mothers do not
nourish young.
11. Strong boney skeleton.
12. Well developed digestive system. (gullet,
stomach, large/small intestine, rectum, cloaca)
13. Most live on dry land but some species are
aquatic.
The Amniotic Egg
• This is the main adaptation that allowed animals to
successfully colonize land and not be reliant on
water for reproduction.
• The egg provides a self contained environment for
the developing embryo. It provides protection, food,
and a moist environment for development.
Parts of the Egg
• Albumen (egg white): Its primary purpose is to
protect the egg yolk and provide additional nutrition
for the growth of the embryo. It is contains many
proteins.
• Air space: Gives air for the embryo to breathe just
prior to hatching.
• Chorion: Membrane that surrounds the embryo
and yolk sac.
• Amnion: Fluid filled sac that cushions the embryo.
• Yolk Sac: Contains stored food for the embryo.
• Allantois: Holds wastes produced by the embryo.
4 Orders of Reptiles
1. Order Squamata – Horny epidermal
scales. Includes snakes and lizards.
2. Order Chelonia – Bodies with 2 bony
shells. Eg. Turtles and tortoises.
3. Order Crocodilia – Alligators,
crocodiles, caimans and gavials.
4. Order Sphenodontia (Formerly known
as Rhynchocephalia) - tuatara
Class Aves (Birds)
• All birds have wings and most birds can fly.
• Flight requires:
– Lightweight – reduced mass
– Airfoil – lift
– Navigation
– Great strength
– High energy
• Virtually every characteristic and body system
supports flight.
• Aerodynamic spindle shaped body with head,
neck, trunk and tail.
Efficient Respiratory System
• Nine air sacs
– Connect to lungs and
centers of bones
– Cools the bird
• Fresh air always
moving
– No dead ends as in
mammals
• Each wing beat
moves air
– Never run out of air
Bones
• The long hollow and porous bones of birds
are thin and slender to aid in flight. Many
bones overtime have fused together to give
support. Eg. The sternum for attachment of
the large flight muscles.
• Honey combed bones
– Air cavities
– Less weight
Beaks & Bills
• Have no teeth; birds are adapted to their
various feeding habits by the structure of their
beaks.
• Their feet are also adapted for specific uses
depending on a birds way of life
Other Important Characteristics
• Have internal fertilization & lay
amniotic eggs.
• Legs with scales, specialized for
perching, walking, swimming or
catching prey
• Complex digestive system with a crop
(storage) and gizzard (grinding).
• Birds have a well developed sense of
sight and balance, average hearing but
a poorly developed sense of taste.
Other Important Characteristics
• Endothermic – constant body temperature
–High temperature = high metabolic rate
–Maintain this high metabolic rate with
efficient respiration, circulation and a
high energy diet.
• Have a 4-chambered heart (2 atria & 2
ventricles) & rapid heart rate.
• Excretory system with no bladder, no
urine. Semi solid nitrogen waste as uric
acid.
Class Mammalia
• Primarily terrestrial, but some live in water
• Have hair/fur on their bodies during part of their
lives
• Have mammary glands, which produce milk to
nourish the young. The shortest nursing period
for mammals is 4 days (Hooded Seal)
• Internal fertilization and embryo development.
• Well developed lungs & a diaphragm which aids
in breathing and divides the thoracic and
abdominal cavity.
Class Mammalia (cont.)
• Efficient circulatory system with a 4
chambered heart and separate
systemic and pulmonary loops
• Endothermic
• 2 Pairs of limbs – 2 pectoral and 2
pelvic
• Have differentiated teeth (incisors,
canines, molars, and pre-molars)
Class Mammalia (cont.)
• Larger more developed brain with a
large cerebrum
• Intelligent behaviour
• High level of parental care for
young.
• 7 cervical (neck) vertebrae
• Non nucleated red blood cells
• Highly developed organ systems.
Class Mammalia (cont.)
• 3 main Subclasses of mammals:
1. Protheria – (Monotremes) Pg. 450 &
767
–Lay and incubate eggs
–Mammary glands but no nipples
–Cloaca
–Live in Australia
–ex. spiny anteater and duckbilled
platypus
2. Metatheria (Marsupials)
• Pouched mammals
• Give birth very early and the young
animal climbs from the mother's birth
canal to the pouch. The young embryo
attaches to a nipple and finishes
development in the pouch.
• Very common in Australia and
surrounding islands. The only marsupial
outside of Australia is the American
Opossum.
3. Eutheria (Placental
mammals)
• All bear live young, which are nourished
before birth in the mother's uterus through a
specialized embryonic organ attached to the
uterus wall, the placenta.
• The embryo is nourished from the blood of
the mother.
Classes of Mammals
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Insectivora
Rodentia
Lagomorphs
Chiroptera
Edentata
Proboscidia
Ungulates (Artiodactyla, Perissodactyla)
Carnivora
Pinnepedia
Cetacea
Sirenia
Primates