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Phylum Chordata

By the end of the Cambrian period, 540 million years
ago, an astonishing variety of animals inhabited Earth’s
oceans. One of these types of animals gave rise to
vertebrates, one of the most successful groups of
animals.
 Four distinctive characteristics define the chordates:
 Notochord
 Dorsal tubular nerve cord
 Pharyngeal pouches (gill slits)
 Postanal tail
 All are found at least at some embryonic stage in all
chordates, although they may later be lost.
Notochord

The notochord is a flexible, rod-like structure derived
from mesoderm.
 The first part of the endoskeleton to appear in an
embryo.
 Place for muscle attachment.
 In vertebrates, the notochord is replaced by the
vertebrae.
Dorsal Tubular Nerve Cord

In chordates, the nerve cord is dorsal to the alimentary
canal and is a tube.
 The anterior end becomes enlarged to form the brain.
 The hollow cord is produced by the infolding of
ectodermal cells that are in contact with the
mesoderm in the embryo.
 Protected by the vertebral column in vertebrates.
Pharyngeal Pouches and Slits


Pharyngeal slits are openings that lead from the
pharyngeal cavity to the outside. They are formed when
pharyngeal grooves and pharyngeal pouches meet to
form an opening.
In tetrapods, the pharyngeal pouches give rise to the
Eustachian tube, middle ear cavity, tonsils, and
parathyroid glands.
Post-anal Tail
The
post-anal tail, along with muscle and the notochord,
provides motility in larval tunicates and amphioxus. It is
reduced to the coccyx (tail bone) in humans.
Four anatomical features that characterize phylum Chordata
Traditional Classification

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Protochordata (Acraniata) are separated from
Vertebrata (Craniata) that have a skull.
Vertebrates may be divided into Agnatha (jawless)
and Gnathostomata (having jaws).
Gnathostomata is subdivided into Pisces with fins
and Tetrapoda, usually with two pair of limbs.
Vertebrates are also divided into Amniota, having an
amnion, and Anamniota lacking an amnion.
Tunicates
‫الزِقيات‬
Ancestral
chordate
Lancelets
‫السهميات‬
Brain
‫المخ‬
Craniates ‫جمجميه‬
Hagfishes
‫سمك الجريث‬
Lampreys
‫سمك الالمبري‬
Head
‫الرأس‬
Sharks, rays
‫الخطوط الشعاعية‬
‫في أسماك القرش‬
Vertebral column
‫العمود الفقري‬
Ray-finned fishes
‫أسماك ذات‬
‫الزعانف الشعاعية‬
Jaws
‫الفكوك‬
Lobe-fins
‫الزعانف‬
‫المفصصة‬
Lungs or lung derivatives
‫الرئة ومشتقاتها‬
Lobed fins
‫الزعانف المفصصة‬
Reptiles
‫الزواحف‬
Legs
‫األرجل‬
Amniotic egg
‫بيضه سلويه‬
Milk
‫لبن‬
Mammals
‫ثدييات‬
Amniotes ‫السلويات‬
A phylogenetic tree of
chordates showing key
derived traits
Amphibians
‫البرمائيات‬
Classification of the Chordata
 There

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are three subphyla in the Chordata:
Subphylum Urochordata: tunicates
Subphylum Cephalochordata: lancelets
Subphylum Vertebrata: fish, amphibians,
reptiles, birds, mammals, etc.
(1) Subphylum Urochordata

The Urochordata (“tunicates” named for the
tough tunic that surrounds the adult) look like
most unpromising candidates to be chordates
and relatives of the vertebrates.

The largest group, the ascidians or sea squirts
(Class Ascidiacea) as adults are marine, sessile,
filter feeding organisms that live either solitarily
or in colonies.
0147.jpg
Ciona intestinalis
(a solitary sea squirt)
Synoicum pulmonaria a colonial sea squirt
Ascidians

Adult ascidians lack a notochord and there is only a
single ganglion in place of the dorsal nerve cord.

Of the five characteristics of chordates adults possess
only two: pharyngeal gill slits and an endostyle.

The adult sea squirt draws water in through an incurrent
siphon and pushes it back out an excurrent one.

Food particles are filtered out in the pharyngeal slits with
mucus from the endostyle used to trap particles.
Figure 23.04
15.4
Larval Ascidian
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Even though the adult ascidian hardly resembles a
chordate its larva does.
Larval ascidians are very small and tadpole-like and
possess all five chordate characteristics previously outlined.
Ascidian metamorphosis


Ascidia searches for a place to settle and then attaches and
metamorphoses into an adult.
During metamorphosis the notochord disappears, the nerve cord
is reduced to a single nerve ganglion and a couple of nerves.
(2) Subphylum Cephalochordata

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Includes 29 species, five of which occur in North
American coastal waters.
All five chordate characters are present in a simple
form.
The dorsal, hollow nerve cord lies just above the
notochord.
Filter feeding is accomplished using pharyngeal slits
and a mucous net secreted by the endostyle.
The circulatory system is closed, but there is no heart.
Blood functions in nutrient transport, not oxygen
transport.
Segmented trunk musculature is another feature
shared with vertebrates.
Amphioxus

Amphioxus (lancelets), is interesting because it displays the
basic chordate characteristics in a simple and obvious form
because of its transparency.

Amphioxus is considered to be the closest living relative of
the vertebrates because it shares several characteristics
with vertebrates that Urochordates do not possess.

Amphioxus is small (3-7 cm long) laterally compressed fishlike animal that inhabit sandy sediments of coastal waters.
It lacks a distinct head and have no cranium.

Amphioxus is a filter feeder. Water enters the mouth and
then is moved by beating cilia through the pharyngeal slits,
where food is trapped in mucus. Cilia then move the food
to the gut.
Amphioxus
Figure 23.09a
Figure 23.09b
Amphioxus
(3) Subphylum Vertebrata


Subphylum Vertebrata shares the basic chordate
characteristics with the urochordates and
cephalochordates.
The animals called vertebrates get their name from
vertebrae, the series of bones that make up the
backbone.
Subphylum Vertebrata = Craniata

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Craniates are chordates that have a head.
Craniates share some common characteristics:
 A skull, brain, eyes, and other sensory organs.
Vertebrates have an endoskeleton (cartilage or bone).
 All have a cranium to protect the brain.
 Almost all have vertebrae to protect the spinal cord.
 Important for muscle attachment.
There are approximately 52,000 species of vertebrates
which include the largest organisms ever to live on the
Earth (Fishes, Amphibians, Reptiles, Birds and
Mammals)
The Origin of Vertebrates

Vertebrates evolved at least 530 million years ago,
during the Cambrian explosion.
 Pikaia was an early chordate discovered in the Burgess
Shale.
 The most primitive of the early vertebrate fossils are
those of the 3-cm-long Haikouella.
 In other Cambrian rocks, paleontologists have found
fossils of even more advanced chordates, such as
Haikouichthys.
 Other early vertebrate fossils include the armored
jawless fishes called ostracoderms from the late
Cambrian.
Pikaia
Ostracoderm
Vertebrate Higher Classification

Two superclasses according to presence of jaws:

Superclass Agnatha - without jaws

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Class Cyclostomata – lampreys
Superclass Gnathostomata – with jaws

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Class Chondrichthyes – sharks, rays, chimaeras
Class Osteichthyes – bony fishes
Class Amphibia – frogs, salamanders
Class Reptilia – snakes, lizards, crocodiles
Class Aves - birds
Class Mammalia – mammals
Fish – Basic Facts


Fish live in nearly every aquatic habitat imaginable.
Fish are aquatic vertebrates characterized by fins,
scales, and gills.
 Fish were the first vertebrates to evolve.
 Fish bring in Oxygen rich water through gills and
remove oxygen poor water through gill slits.
 Closed circulatory system.
 Four chambered heart.
 Swim bladder controls buoyancy.
 Most are egg laying.
 Most move by contracting opposite muscles (S
Shaped).
Groups of Fish

Jawless Fish:
 Have mouths of soft tissue with no true teeth.
 Have no bones.
 Only vertebrates with no vertebral column as adults.
 Lampreys, Hagfish
 Chondrichthyes:
 Skeleton built entirely of cartilage.
 Sharks, sea rays.
 Osteichthyes:
 Bony Fish.
 Majority of fish fall in this order.
 Carp, sea horse, perch, etc.
Lamprey – Jawless Fish
Ammocoete Larva of Lampreys

Lampreys have a freshwater larval stage, the
ammocoete, that resembles amphioxus.
 Filter feeders
 Closely approaches ancestral body plan.
Chondrichthyes
Osteichthyes
Lake trout
Whitefish
Sturgeon
Walleye
Bluegill
Yellow perch
Amphibians – Basic Facts
Amphibian = “double life”.
 Live in both water and land.
 Most larvae are fish-like; adults are terrestrial.
 Larvae respire through skin and gills; Adults use
lungs.
 Descendants of ancestral organisms that evolved
some adaptations for life on land.
 First appeared 360 million years ago.
 External fertilization.
 Closed circulatory system; three chambered heart.

The Life Cycle of a Frog
Section 30-3
Adult
Frog
Adults are typically ready to
breed in about one to two years.
Frog eggs are laid in water and
undergo external fertilization.
Fertilized Eggs
The eggs
hatch into
tadpoles a
few days to
several
weeks later.
Young
Frog
Tadpoles
Tadpoles gradually grow limbs, lose their tails and gills, and
become meat-eaters as they develop into terrestrial adults.
Groups of Amphibians
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Salamanders:
 Long bodies and tails.
 Adults are carnivorous.
 Usually live in moist woods.
Frogs and Toads:
 Lack tails.
 Frogs have long legs and are usually tied to water.
 Toads have shorter legs, not closely tied to water.
Caecilians:
 Legless animals that burrow in moist soil.
 Have fishlike scales.
Spotted Salamander
Fire Bellied Toad
Poison Dart Frog
Caecilian
Reptiles – Basic Facts

All reptiles have:
 Dry, scaly skin – helps prevent loss of body water
in dry environments.
 Terrestrial eggs – first animals to develop amniotic
eggs that didn’t need to be deposited in water
 Respire using lungs.
 Closed circulatory system.
 Heart = two atria; one or two ventricles.
 Internal Fertilization; Most are egg-laying.
 Ectotherms – cannot internally regulate body
temperature; cannot live in cold climates
 Behavior controls body temp. (swimming, burrowing,
basking, etc.)
Groups of Reptiles

Lizards and Snakes:
 Have legs & clawed toes (Lizard); external ears,
moveable eyelids.
 Highly evolved specialized forms (venom).
 Crocodiles and Alligators:
 Long, typically broad snout and squat appearance.
 All are carnivorous.
 Protective of young; carry hatchlings in their mouth.
 Live in tropics and subtropics.
 Alligators live in freshwater.
 Crocodiles live in fresh or saltwater.
 Turtles and Tortoises:
 All are shelled
 Turtles are aquatic; tortoises are terrestrial
 Tuatara:
 Primitive reptiles found on small, remote islands.
Coral Snake
Tuatara
Sea Turtle
Nile Crocodile
Galapagos Tortoise
North American Alligator
Birds – Basic Facts

Nearly 10,000 modern bird species.
 Birds are closely related to reptiles (scales on legs).
 Have outer covering made of feathers, two legs used for
walking or perching, and forelimbs modified into wings.
 Feathers separate birds from all other animal species.
 Feathers provide insulation for warmth; can generate on
body heat.
 Beak/Bills adapted to type of food they eat.
 Highly efficient respiratory system; lungs only exposed to
Oxygen rich air
 Internal fertilization; amniotic eggs.
Section 31-2
Birds
Have the following adaptations to flight
Efficient
respiratory
system
Efficient
circulatory
system
Wings
Feathers
Strong chest
muscles
which are
that also
that power
that provide
that ensure
Homologous to
front limbs in other
vertebrates
Provide
warmth
Upward and
downward wing
strokes
One-way flow
of O2-rich air
O2 distribution
to body tissues
Groups of Birds

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More than thirty orders of birds
Some of the most common
 Perching Birds – largest order; many are songbirds
(sparrows, crows, cardinals, etc.)
 Birds of Prey – fierce predators with hooked bills;
large talons (condors, hawks, owls, eagles, etc.)
 Herons & Relatives – Wade in aquatic habitats
(storks, herons, cranes)
 Ostriches & Relatives – flightless birds move by
running or swimming (ostriches, emus, etc.)
Purple Finch
Stork
Red-Tailed Hawk
Emu
Mammals – Basic Facts

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First true mammals appeared 220 million years ago.
Mammals flourished after dinosaurs became extinct – 65
million years ago.
Basic characteristics:
 Hair.
 Mammary glands – produce milk to nourish young.
 Breathe air.
 Four chambered heart.
 Endotherms – can generate own body heat.
 Internal fertilization; care for young.
Groups of Mammals
 The mammals are divided into three groups:
monotremes, marsupials, and placentals.
 Group Monotremes: are found only in Australia and
New Guinea, and include the platypus and two
species of spiny anteaters, also known as echidnas.
Monotremes lay eggs.
 All mammals except monotremes have embryos that
develop in the uterus of the female reproductive tract.
 Group marsupials: embryos are only in the uterus for a
short time and are then born at immature stage of
development. After birth, they crawl to a nipple, firmly
grasp it, and complete their development.
 In many marsupial species, this post-birth
development takes place in a protective pouch.
 Group Placenta:
• Most mammal species are placental mammals.
• Compared to marsupials, placental mammals retain
their young in the uterus for a much longer period, so
that offspring complete their embryonic development
before being born.
• The bat, mole, impala, whale, seal, monkey, and
cheetah exemplify the radiation of mammals into
nearly all habitats, with bodies adapted to their varied
lifestyles.
• The largest group of placental mammals are the bats
and rodents.