Kingdom Animalia
Phylum Chordata
“Vertebrates”
• Organisms in this phylum are segmented
animals with four distinctive features
• Dorsal hollow nerve cord
• Stiff notochord
• Pharyngeal slits behind the mouth
• Muscular post-anal tail
• Coelom
• Bilateral symmetry
Phylum Chordata
“Vertebrates
• The simplest chordates are tunicates and lancelets.
• These are marine invertebrates
POST-ANAL TAIL
DORSAL, HOLLOW
NERVE CORD
Tunicates
PHARYNGEAL
SLITS
Muscle
segments
Mouth
NOTOCHORD
Simplest Chordates
LARVA
Lancelets
NOTOCHORD
DORSAL, HOLLOW
NERVE CORD
Head
Mouth
Water
exit
Pharynx
PHARYNGEAL
SLITS
Digestive
tract
Anus
Segmental
muscles
POST-ANAL
TAIL
Simplest Chordates
• Most chordates are
vertebrates.
• Their
endoskeletons
include a skull.
• Their backbone is
composed of
vertebrae.
Vertebrae
Backbone
Vertebrates
A skull and a backbone are hallmarks of vertebrates
Skull
• Exception: Lampreys lack hinged
jaws.
• They are classified as agnathans.
• Jaws evolved by the modification of
skeletal supports of the gill slits.
Gill
slits
Skeletal
rods
Skull
Mouth
Vertebrates
Most vertebrates have hinged jaws.
• Fish are jawed vertebrates with gills and paired
fins.
• Cartilaginous fish diverged before bony skeletons
appeared.
• Examples: Shark and ray
Class Chondrichthyes
Cartilaginous Fish
• Bony fishes are more diverse and have
– more mobile fins
– operculi that move water over the gills
– a buoyant swim bladder
BONY SKELETON
OPERCULUM
Gills
Class Osteichthyes
SWIM BLADDER
Bony fish
• Three sub-classes of
bony fish:
• Ray-finned
• Lobe-finned
• Lungfish
• Evolutionary evidence
suggests that tetrapods
evolved from lobefinned fish.
Rainbow trout,
a ray-fin
Coelacanth,
a lobe-fin
Class Osteichthyes
• Air-breathing lungfishes that developed skeletonreinforced appendages probably gave rise to the first
amphibians.
Bones
supporting gills
Typical tetrapod limb skeleton
• Class Amphibia is represented today by:
• frogs
• toads
• Salamanders
• Their limbs allow them to move on land.
• However, amphibian larvae must develop in water.
Class Amphibia
1st Land Vertebrates
• Key Characteristics:
• Body Temperature: Ectotherms – obtain their body heat
from the external environment
• Reproduction: Females lay eggs in water, and males
fertilize. Eggs do not have shells or outer coverings.
• Examples:
• Frogs and toads
• Salamanders and newts
• Caecilians (worm-like animal burrows in soil)
Class Amphibia
• Reptiles have more terrestrial
adaptations than amphibians.
• Class Reptilia is able to live on
land due to:
• waterproof scales
• a shelled, amniotic egg
• Modern reptiles are still
ectotherms.
• They warm their bodies by
absorbing heat from the
environment.
Class Reptilia
1st amniotic egg
• Class Aves has:
• scales
• amniotic eggs
• Wings
• Feathers
• an endothermic
metabolism
• hollow bones
• a highly efficient
circulatory system
Class Aves
1st Endotherms
Wing claw
(like reptile)
Teeth
(like reptile)
Feathers
Long tail with
many vertebrae
(like reptile)
• Birds share many characteristics in common with
reptiles.
• Scientists believe that birds’ feathers are evolved
scales.
• Consider the scaly skin of birds’ feet.
Class Aves
• Mammals also evolved from reptiles.
• Mammals are endothermic.
• There are two unique mammalian characteristics:
• Hair, which insulates the body
• Mammary glands, which produce milk that
nourishes their young.
Class Mammalia
• Monotremes: a few mammals lay eggs
• Example: duck-billed platypus
Class Mammalia
Monotremes
• Marsupials have a short
gestation.
• The tiny offspring
complete development
attached to the mother’s
nipple, usually inside a
pouch.
• Example: kangaroos
Class Mammalia
Marsupials
• Most mammals are eutherians,
also called placentals,
• They have a relatively long
gestation.
• Complete embryonic
development occurs within
the mother.
Class Mammalia
Placental Mammals
• A traditional phylogenetic tree is based on
patterns of embryonic development and some
fundamental structures.
Phylogeny of the Animal
Kingdom
Porifera
Platyhelminthes
Cnidaria
Mollusca
Arthropoda
Chordata
Nematoda
Annelida
Pseudocoelom
PROTOSTOMES
DEUTEROSTOMES
Coelom from
cell masses
Coelom from
digestive tube
No body cavity
Echinodermata
True coelom
Body cavity
Radial
symmetry
No true tissues
Bilateral
symmetry
True tissues
Ancestral protists
Present
day