Phylum Chordata and The Classes Under It

WEEK 6-7: PHYLUM CHORDATA: INTRODUCTION
 Derived from the Latin word chorda,
meaning “cord”, “string”.
 They can be aquatic, terrestrial,
amphibious, and aerial.
 They are bilaterally symmetric.
 They are also triplobastic.
 They have a true body cavity
(eucoelomatic).

 They primarily reproduces sexually, with
fertilization being either external or internal.
 Some tunicates can reproduce asexually through
budding.
 Development varies:
o oviparous
o ovoviviparous
o viviparous

 And like echinoderms, chordates are
deuterostome.
 They also have a complete digestive
system.
 They also have cephalization.
 They have a closed circulatory system.
 They are classified into three subphyla:
oUrochordata (tunicates)
oCephalochordata (lancelets)
oVertebrata (vertebrates).

What makes a chordate a
chordate?

Four Main
Characteristics of
Chordates
• Notochord
• Dorsal Nerve Cord
• Pharyngeal Slits
• Post-Anal Tail

WEEK 6-7: PHYLUM CHORDATA: CHARACTERISTICS
NOTOCHORD
 A flexible rod that lies
along the
anteroposterior axis (i.e.
from top to bottom) of
the body of the
organisms.
 Situated between the
gastrointestinal tract and
the spinal cord.

NOTOCHORD
 In vertebrates, the
notochord is
replaced with a
vertebral column
(spine) past the
embryonic stage.
 It provides support
and increases
swimming efficiency

DORSAL NERVE CORD
 A hollow tube derived
from the ectoderm
during the embryonic
stage of vertebrates.
 Lies dorsal to the
notochord.

DORSAL NERVE CORD
 Made up of the nerve
fibers that ultimately
develop into the central
nervous system.
 Protected by the
vertebral column.

PHARYNGEAL SLITS
 The region below the
mouth (or oral cavity)
and extends to the
outside (environment)
 Used by invertebrate
chordates for filter
feeding.

PHARYNGEAL SLITS
 In aquatic vertebrates,
such as fish, the
pharyngeal slits are
eventually transformed
into gill supports or into
jaw supports (as in
jawed fishes).

PHARYNGEAL SLITS
 As for other
vertebrates, such as
mammals and birds,
the pharyngeal slits
are present at the
embryonic stage and
then integrate as
parts of the ear and
tonsils.

POST - ANAL TAIL
 The posterior
elongation of the body
that extends beyond
the anus.
 In aquatic chordates, it
has skeletal elements
and muscles which is
essential to the
organism’s locomotion

POST - ANAL TAIL
 In humans and apes,
this tail is vestigial,
meaning it can be
found during
embryonic
development but
reduces in size or
becomes vestige at
birth.

WEEK 6-7: PHYLUM CHORDATA: KEY POINTS
 The notochord provides skeletal support, gives the
phylum its name, and develops into the vertebral
column in vertebrates.
 The dorsal hollow nerve cord develops into the
central nervous system: the brain and spine.
 Pharyngeal slits are openings in the pharynx that
develop into gill arches in bony fish and into the
jaw and inner ear in terrestrial animals.
 The post-anal tail is a skeletal extension of the
posterior end of the body, being absent in humans
and apes, although present during embryonic

PHYLUM CHORDATA
A Tribute to the Diversity We
Know

Let’s start at the very beginning . . .
• Phylum Chordata is divided into three
subphyla:
-Subphylum Urochordata
-Subphylum Cephalochordata
-Subphylum Vertebrata

Subphylum Urochordata
 Also called as tunicates.
 AII urochordates are
sessile or permanently
pelagic forms.
 The adults are mostly
degenerated and un-
segmented.

 They possess a notochord,
a hollow nerve cord and a
post-anal tail during their
larval stage.
 Their body has more than
two cell layers and includes
tissues and organs.
 They have a U-shaped gut.

Their body has no coelomic
body cavity.
Their body is wholly enclosed
in a 'tunic' of secreted protein
and cellulose-like material.
They are hermaphroditic,
normally with only one ovary
and testis.

 They have a nervous
system composed of an
anterior ganglion.
 They have no excretory
organs.
 Urochordates has a
distinct larval stage.

 All are filter feeders.
 They live in marine
environments.
 Example: Ascidians,
Salps, Larvaceans

• Urochordates show unique exceptions to typical
chordate traits:
 Retrogressive Metamorphosis – Larvae have
chordate features but lose them as sessile adults.
 Alternation of Generations – Some species switch
between sexual and asexual reproduction.
 Formation of Colonies – Many tunicates
reproduce by budding, forming interconnected
colonies.

Subphylum Cephalochordata
 Small marine invertebrates,
found mainly in shallow water.
 The body is fish-like, slender,
translucent, and tapered at both
ends, with a post-anal tail
 They usually have a head and a
tail.
 Appendages are absent.

 Due to the shape of the body,
they are often called lancelets.
 Median fins are present but
lack paired fins.
 Epidermis is single-layered.
 Notochord extends from the
anterior end to the posterior end.

 Body muscles are arranged on
both sides of the body.
 The ventral mouth is surrounded
by small tentacles.
 The pharynx is large and
comprises numerous gill slits,
opening into the atrium.

 The circulatory system is
closed-type and well-developed
without a specialized heart.
 Blood is colorless and lacks
respiratory pigment.
 Excretion occurs by
protonephridia with
solenocytes.

Sexes are separate.
Gonads are several pairs and
ductless.
Fertilization occurs externally.
Development is indirect,
including a free-swimming,
asymmetrical planktotrophic
larva.

Example organisms
are:
o Branchiostoma
lanceolatum
o Asymmetron
lucayanum
o Epigonichthys
cultellus

RECALL:
What are the characteristics of
Subphylum Urochordata?
How about Subphylum
Cephalochordata?
How are they different from each
other?

Subphylum Vertebrata
Derived from the Latin word
vertebratus meaning "having
vertebrae" or "possessing a
backbone.“
Animals with a vertebral column
(backbone or spine), and a cranium
(skull) are classified under this
subphylum.

Possesses the four defining traits
during their embryonic stage.
Incredibly diverse, with over 62,000
identified species.
Sadly, many vertebrate species today
are facing the threat of extinction
primarily due to habitat loss and
pollution.

A vertebrate is an animal that has all of
the following characteristic features at
some point in its life:
- A stiff rod running through the
length of the animal
- A bundle of nerves run above the
vertebral column the alimentary canal
exists below it.

A vertebrate is an animal that has all of
the following characteristic features at
some point in its life:
- The mouth is present at the anterior
portion of the animals or right below it.
- The alimentary canal ends in the anus,
which opens to the exterior.
- The tail extends after the anus.

Vertebrates reproduce sexually, and
almost all of them have separate male
and female sexes.
Generally, aquatic species have external
fertilization, whereas terrestrial species
have internal fertilization.

Three reproductive stages:
 Ovipary – development of an embryo outside
the mother’s body
 Ovovivipary – development of an embryo inside
the mother’s body until it hatches
 Vivipary – development and nourishment of an
embryo within the mother’s body

SEVEN CLASSIFICATIONS OF VERTEBRATA
1. Class Mammalia
(Mammals)
2. Class Aves (Birds)
3. Class Reptilia
(Reptiles)
4. Class Amphibia
(Amphibians)
5. Class Osteichthyes
(Bony Fishes)
6. Class Chondrichthyes
(Cartilaginous Fishes)
7. Class Agnatha (Jawless
Fishes)

Class Agnatha
 Derived from the Greek words
a (without) and gnathos (jaws).
Consists of primitive jawless
fishes characterized by circular
mouths and small, sharpened
teeth.
Most members of this class are
parasites and scavengers.

Class Agnatha
Have unique feeding habits.
 Morphologically, they bear
resemblance to eels but lack true
jaws
Showcases unique adaptations and
evolutionary traits that set them
apart from other vertebrate
classes.

Class Agnatha
Members of the class Agnatha
reproduce in the water through
external fertilization.
Mostly oviparous
Among the representatives of Class
Agnatha are hagfish and lampreys.

Class Chondrichthyes
Characterized by the cartilaginous
skeleton.
Derived from Greek words
chondros (cartilage) and ichthys
(fish).
They are mostly marine fishes.
They contain a very powerful pair
of jaws. The mouth is present
ventrally.

They are true jawed vertebrates,
possessing well-developed
respiratory, excretory, and
circulatory systems.
They are covered in scales that
provide protection and aid in their
aquatic lifestyle.
They are oviparous.

Their primary mode of respiration
is through gills.
Unlike other fish, they possess
two-chambered hearts and have
skeletons composed entirely of
cartilage.
They are poikilothermic
organisms.

They contain cartilaginous
endoskeleton; the deposits of
calcium salts provide strength to
it.
The notochord is present
throughout life.
Most of them contain a
heterocercal tail.

Their teeth are modified
placoid scales and are not
attached to jawbones.
They are predatory fishes.
They contain a brain and a
spinal cord, which is
protected by vertebrae.

Sense organs are well
developed.
The digestive system comprises
a mouth, pharynx, stomach,
intestine (straight) and cloaca
present on the ventral side.
Members include sharks, rays,
skates and sawfish.

Class Osteichthyes
Also known as “bony fishes”
derived from Greek words osteon
(bone) and ichthys (fish).
Characterized by their skeleton
which is composed primarily of
bone rather than cartilage.
The largest class of vertebrates
today.

Class Osteichthyes
They have a skeleton made up of
true bones.
Found in a wide range of aquatic
habitats (saltwater and freshwater).
Divided into two subclasses:
1. Sarcopterygii- lobe-finned fish
2. Actinopterygii- ray-finned fish

Class Osteichthyes
 Lobe-finned fish have fleshy,
lobed fins that are thought to be
evolutionary relatives of the fins
seen in amphibians.
 Ray-finned fish have fins
supported by long, flexible bony
rays.

Class Osteichthyes
 Paired and median fins are
present, which are supported by
long rays of cartilage or bone.
 The tail is mostly homocercal.
 They contain a swim bladder or
air bladder.
 The mouth is terminal.

Class Osteichthyes
 They contain four pairs of gills and
an operculum.
 The sarcopterygians, lungfishes
and lobe-finned fishes contain
lungs.
 The skin is covered by bony dermal
scales known as ganoid, cycloid or
ctenoid scales.

Class Osteichthyes
 They are poikilotherms.
 The heart is two-chambered.
Lungfishes have a three
chambered heart.
 The brain has a small
olfactory lobe and
cerebellum.

Class Osteichthyes
 The lateral line organ
contains hydrodynamic
receptors.
 Cloaca is absent, different
genital and anal openings are
present.
 They are ammonotelic and
have mesonephric kidneys.

Class Osteichthyes
Sexes are mostly separate but
some are hermaphrodites.
They are mostly oviparous.
Fertilization is mostly external
and direct development.
In the male Hippocampus, the
brood pouch is present, where
eggs incubate.

Class Amphibia
Derived from the Greek words
amphi (both) and bios (life).
A diverse group of
approximately 4,000 different
species that undergo a unique
life cycle.
They can live both on land and
in water.

Class Amphibia
They are ectothermic animals,
found in a warm environment.
Their body is divided into head
and trunk.
The skin is smooth and rough
without any scales, but with
glands that make it moist.

Class Amphibia
They have no paired fins.
They have two pairs of limbs
for locomotion.
They respire through the lungs
and skin.
The heart is three chambered.
The kidneys are mesonephric.

Class Amphibia
They possess ten pairs of cranial
nerves.
The lateral line is present during
their development.
The sexes are separate and
fertilization is usually external.
Breeding occurs in water.

Class Reptilia
Derived from the Latin word
reptilis which means creeping
or crawling.
The first class of organisms to
adapt to life on land.
They are cold-blooded animals.
The skull of the reptiles is
modified.

Class Reptilia
These are creeping and
burrowing terrestrial animals
with scales on their body.
Their skin is dry, and rough,
without any glands.
The body is divided into head,
neck, trunk, and tail.

Class Reptilia
 The respiration takes place with
the help of the lungs.
 The skull is monocondylic.
 Limbs may or may not be
present.
 The heart is 3 chambered.
 The nervous system comprises
12 pairs of cranial nerves.

Class Reptilia
 Reptiles do not have external
ear openings.
 They possess a typical cloaca.
 Reptiles are generally uricotelic.
 Fertilization is internal.
 They are oviparous.
 Development is direct.

Class Aves
 Derived from the Latin
word avis which means
bird.
 Characterized by feathers
and toothless beaked
jaws with approximately
9,000 species.

Class Aves
 Warm-blooded animals
 Their forelimbs are modified into
wings.
 They have well-developed flight
muscles that help during the flight.
 Their hind limbs are adapted for
walking, hopping, perching,
grasping, wading and swimming.

Class Aves
 There are epidermal scales on their
legs.
 The endoskeleton is bony with long
hollow bones filled with air cavities,
known as pneumatic bones.
 Their spindle-shaped body minimizes
resistance of the wind.

Class Aves
 The feathers help in preventing
heat loss and reduce air friction by
providing passage to the air.
 There is no skin gland except the oil
gland.
 The lower and upper and jaws are
modified into a beak.

Class Aves
 They have no teeth.
 They have sharp eyesight.
 The alimentary canal has a crop and
a gizzard.
 They have spongy and elastic lungs
for respiration.
 The special vocal organ called syrinx
is present at the base of trachea.

Class Aves
 Their heart is four-chambered.
 RBCs are oval, nucleated and
biconvex.
 12 pairs of cranial nerves are present.
 They have a single ovary and oviduct
on the left side.
 All the birds are oviparous and
exhibit sexual dimorphism.

Class Mammalia
 Derived from the Latin word
mamma which means breast or
mammary gland.
 Warm-blooded animals who give
birth to their younger ones.
 The most dominant form of
animals found in almost all types
of habitats.

Class Mammalia
 They have mammary glands that
help them produce milk to feed
their younger ones.
 Presence of region of the brain
known as Neocortex.
 Their skin possesses oil glands
and sweat glands.

Class Mammalia
 The fur of hair throughout the
body which helps animals adapt
to their environment.
 They are heterodont.
 Mammals also possess cervical
vertebrae.

Class Mammalia
 The skull is dicondylic.
 The trunk is divided into thorax
and abdomen.
 The mammals respire through
lungs.
 Good sense of hearing as
mammals are aided with 3
middle ear bones.

Class Mammalia
 Mammals have a four-
chambered heart.
 The brain is well developed
divided into cerebrum,
cerebellum and medulla.
 They possess 12 pairs of cranial
nerves.

Class Mammalia
 Exhibit one of the most
advanced forms of
diaphragms.
 The mammals can lay eggs
also.
 They are known as
viviparous.

In vertebrates, the heart structure varies. Which
class is correctly matched with its heart
chambers?
Fish – Three-chambered heart
Amphibians – Four-chambered heart
Birds – Four-chambered heart
Reptiles – Two-chambered heart

What is the main function of the notochord in
chordates?
Aids in digestion
Provides skeletal support
Produces red blood cells
Helps in respiration

Which reproductive strategy involves the
development of an embryo inside the mother’s
body and with direct nourishment and care from
her?
Ovipary
Ovovivipary
Vivipary
Asexual reproduction

Which vertebrate class includes organisms with a
two-chambered heart and gills for respiration?
Amphibia
Mammalia
Reptilia
Osteichthyes

Which class of vertebrates is known for having
lightweight skeleton and the ability to fly?
Mammalia
Reptilia
Aves
Amphibia

TRUE OR FALSE
The swim bladder in bony fish helps
regulate buoyancy.

TRUE OR FALSE
Class Reptilia are generally
ammonuletic.

TRUE OR FALSE
Amphibians rely entirely on their lungs
for respiration.

TRUE OR FALSE
In vertebrates, the notochord eventually
develops into the vertebral column.

TRUE OR FALSE
The excretory organs are present in
urochordates.

Phylum Chordata and The Classes Under It

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