The Chordates
Also Known As…
Animals With Some Real Spine!
What is a “Chordate”?
• A chordate is an animal with a nerve
cord that runs along their back.
• All chordates have gill slits near their
throats either in their adult lives or
sometime in their developmental
stages.
• All of them have a tail at some point in
their lives or development.
• All chordates show bilateral symmetry.
Chordates & Vertebrates
• All vertebrates are chordates but not all
chordates are vertebrates.
• There are two early classes of chordates
called Urochordata and Cephalochordata.
• The Uruchrodata are small marine animals
known as tunicates.
• The Cephalochordata are the lancelets (also
small marine animals).
• Neither the tunicates or the lancelets have a
backbone (vertebral column). They do have
the nerve cord but no bony vertebrae to
protect it so they are not classed as
vertebrates.
What is a “Vertebrate”?
• A vertebrate is a animal with a backbone
made of cartilage or bone which serves to
protect the dorsal nerve cord.
• You will also see in the vertebrates:
– A skull to house their enlarged brains.
– Well-developed internal cavities that house the
internal organs.
– A ventral heart that pumps blood throughout a
circulatory system.
– Gas exchange through the use of gills or lungs
depending on the habitat/lifestyle of the organism.
• Vertebrates include the jawless fishes,
cartilaginous fishes, bony fishes, amphibians,
reptiles, birds and mammals (seven classes).
Class Agnatha
• The agnathans are the
jawless fishes. Members of
this group include the
lampreys and hagfish.
• There are very few
agnathan species alive
today.
• The lampreys are
ectoparasites while the
hagfish is a scavenger.
• AND DON’T DO STUFF LIKE
THIS!
Class Chondrichthyes
• The chondrichthyans are the cartilaginous
fish. Their skeleton is internal as is ours
but it is made of cartilage rather than
bone.
• The groups includes sharks, rays and
skates.
• They have two sets of paired fins –
pectoral and pelvic fins.
• Breathing is done as water moves over the
gills as they swim – stop swimming and
you die.
• Sharks are ovoviviparous – females keep
fertilized eggs internally and give birth to
live young.
Chondrichthyes
Class Osteichthyes
• Osteichthyans are the bony fish. Their
internal skeleton starts as cartilage but it is
replaced with bone.
• Flat, smooth, light-weight scales cover the
body.
• They use gills to breathe but they are covered
by an operculum – a bony plate that pumps
water over the gills so bony fish can still
breathe even when they are not moving.
• Most bony fish have swim bladders that help
suspend the fish in water. The lungfish uses
the swim bladder as a lung to breathe.
• Most fish lay eggs and release sperm
externally and then leave. The sperm swim to
fertilize the eggs. Fish hatchlings never know
their real parents!
Osteichthyes
Class Amphibia
• The amphibians are an important
evolutionary species as they were the first
animals to leave the water and live on the
land.
• All amphibians still need the water (usually
freshwater) in their early stages but develop
lungs to breathe air out of the water as
adults.
• The frog has a three-chambered heart.
• Air is acquired by diffusion through the lungs,
skin or lining of the mouth depending on the
species.
• Amphibians reproduce very similarly to fish –
another example of poor parenting!
• Common amphibians include frogs, toads,
salamanders and newts.
Amphibia
Class Reptilia
• The reptiles include alligators, crocs,
turtles, lizards and snakes.
• Reptiles picked up where amphibians
left off with their adaptations to a
terrestrial lifestyle.
– They do not need water to reproduce.
– They have eggs that have a hard shell to
minimize water loss.
– Fertilization is internal.
– Tough, scaly skin restricts water loss.
– Kidneys can form highly concentrated
urine so water can be returned to the body.
• The lungs of reptiles are considerably
larger than the amphibians.
Reptilia
Class Aves
• The avians are the birds.
• They have developed from reptiles and share
a few characteristics
– Scales on legs.
– Large-yolked eggs in a firm shell.
– No metamorphosis in young.
• Birds differ from the previous groups
discussed:
– They are endotherms – maintain an internal body
temperature. (Others so far have been ectotherms.)
– Feathers – which evolved from scales – they help
preserve heat and allow for flight.
– Hollow bones keep them light for flight.
– Air sacs branch off from the trachea keep the bird
respired and buoyant during flight.
Aves
Class Mammalia
• The mammals have the key
characteristic of mammary glands
which are used to feed their
young.
• Other key traits of mammals:
– Endothermic
– Covered in hair or fur
– Four-chambered heart
Mammalia
That’s All I Got…