Download COVENANT UNIVERSITY COLLEGE OF

COVENANT UNIVERSITY
COLLEGE OF SCIENCE AND TECHNOLOGY
DEPARTMENT OF BIOLOGICAL SCIENCES
Programme: Applied Biology and Biotechnology
Course Code: BLY 223
Course Title: BASIC Chordate Zoology
Units: 3
Course Lecturer: Ejoh S.A
Course Coordinator: Ayanda O.I
Semester/Session: Omega, 2013/2014
Course Outline
Module I: Introduction to Chordate Zoology
Week 1 General characters and Taxonomical
classification of Phylum Chordata up to orders
- Origin of Chordata.
Week 2 Functional morphology, general diversity and
adaptations of the types included with special
emphasis on the adaptations to their mode of
life and environment.
Module II: Pro-Chordata and Agnatha:
Week 3 General characters, classification and
evolutionary significance - Type study:
Balanoglossus, Amphioxus, Ascidians
Week 4 Affinities and systematic position of Sub
phylum Hemichordata, Cephalochordata and
Urochordata
Week 5 Agnatha :General characters and affinities Type study - Petromyzon
Module III: Sub Phylum Vertebrata: Class Pisces:
Week 6 Class Pisces: General characters, classification
and evolutionary significance - Origin of fishes
– Type study: Scoliodon, Tilapia
Week 7 Types of scales and fins - Accessory
respiratory organs - Air bladder - Parental care
- Migration - Economic importance.
INTRODUCTION TO PHYLUM CHORDATA
The Phylum Chordata includes the well-known vertebrates
(fishes,
amphibians,
reptiles,
birds,
mammals).
The
vertebrates and hagfishes together comprise the taxon
Craniata. The remaining
chordates are the
tunicates
(Urochordata), lancelets (Cephalochordata), and, possibly,
some odd extinct groups.
With few exceptions, chordates are active animals with
bilaterally
symmetric
bodies
that
are
longitudinally
differentiated into head, trunk and tail.
Chordates are well represented in marine, freshwater and
terrestrial habitats from the Equator to the high northern and
southern latitudes.
Characteristics
The three most important characteristics of phylum chordate
are:
1. They possess a notochord either throughout or during
early embryonic development.
2. Dorsal hallow nerve chord.
3. Paired gill slits on the sides of pharynx
1. Notochord
The notochord is a flexible rod-like structure, which is
enclosed by a fibrous sheath and extends the length of the
body in larva and/or adult.
It is first part of skeleton to form in embryo
In primitive chordates the notochord persists through life
while in higher chordates, the notochord is replaced by a
vertebral column of bone. The remnants of the notochord
remain as ―intervertebral discs‖
Functions
Provides basic support and serves as main axis for
muscle attachments to permit ―fishlike‖ undulatory
movements
In some non-vertebrate chordates and fishes the
notochord persists as a laterally flexible but
incompressible skeletal rod that prevents telescopic
collapse of the body during swimming.
In most chordates the notochord is replaced by a
vertebral column of bone.
Remnants of the notochord remain as ―intervertebral
discs‖
2. Dorsal hallow nerve cord
A fluid-filled tube of nerve tissue that runs the length nerve
cord is ventral & paired
Present throughout embryonic and adult life
Functions
In chordates the nerve cord is a single dorsal hollow
nerve cord front end usually enlarged to form brain
3. Pharyngeal (gill) slits
Pharyngeal gills are slit-like opening sliding from throat to
outside
In some groups they are only found in embryo and lost as
adults
Functions
It was first evolved as a filter feeding apparatus
It is still used by some organisms to filter water for food
and in others as gills
4. Endostyle or thyroid gland
This is a specific kind of tissue found only in chordates.
Functions
It was originally part of the feeding apparatus
The endostyle secretes mucus and traps food inside the
pharyngeal cavity. Eg. lamprey larva
In most chordates the same tissue has become an
endocrine
This gland in the neck region that helps control
metabolism
5. Post-anal tail
The post- anal tail in aquatic chordates it provides motility, it
was designed for propulsion in water, especially for larval
forms and fish
Fish later gained fins to increase efficiency
In terrestrial chordates it became a tail for leverage and
balance, not for movement
In humans ―tailbones‖ is its remnant
Additional, more variable, Chordate characteristics are also
shared by many or most species:
6. Bilateral symmetry
7. Tube within a tube body plan
8. Segmented muscles called myomeres or myotomes in fish
9. Cephalization
10.Ventral heart
11. Endoskeleton: most members have an internal skeleton of
cartilage and/or bone
<5% of all animals that have ever lived have backbones
CLASSIFICATION OF PHYLUM CHORDATA
The phylum Chordata is sub-divided into three sub- phyla
1. Sub phylum Urochordata or Tunicata
2. Sub-phylum Cephalochordata or Lancelet
3. Sub phylum Vertebrata or Crainiata
Closest Relatives
Hemichordates ("half chordates") have some features similar
to those of chordates: branchial openings that open into
the pharynx and look rather like gill slits; stomochords,
similar in composition to notochords, but running in a circle
round the "collar", which is ahead of the mouth; and a dorsal
nerve cord — but also a smaller ventral nerve cord.
There are two living groups of hemichordates.
 The solitary enteropneusts, commonly known as "acorn
worms‖
 Pterobranchs are colonial animals
Sub phylum Urochordata or Tunicata
 Sub-phylum Urochordata or Tunicata are strictly marine
 There are roughly 1,600 species of urochordates; most
are small solitary animals but some are colonial,
organisms. Nearly all are sessile as adults but they have
free-swimming, active larval forms.
 The notochord is restricted to the tail region of the larva
and disappears in the adult
 Urochordates are unknown as fossils.
 Examples – Ascidia(sea squirt), salpa and doliolum
Sub-phylum Cephalochordata or Lancelet
 This sub-phylum contains only about 20 species of sandburrowing marine creatures.
 The notochord extends throughout the length of the
animal dorsally
 Cephalochordata include the amphioxus and lancelets.
Sub phylum Vertebrata or Crainiata
 Most complex/advanced group of animals-one
explanation for their diversity and dominance is that, in
general, vertebrate species have a lot more genes
o flies
o
o
 Fish became the 1st true vertebrates
 Notochord is replaced in the adult either wholly or partly
by a cartilaginous or bony segmented vertebral column
HEMICHORDATA
Balanoglossus "acorn worms",
Balanoglossus
is
an
ocean-dwelling
acorn
worm
(Enteropneusta) genus of great zoological interest because it
is, like Hemichordates, an "evolutionary link" between
invertebrates
and
vertebrates.
Balanoglossus
is
a
deuterostome, and resembles the Ascidians or sea squirts, in
that it possesses branchial openings, or "gill slits", but no
notochord and no nerve cord. It does have a stomochord,
however, which is gut chord within the collar. Their heads
may be as small as 2.5 mm (1/10 in) or as large as 5 mm (1/5
in).
External Characters
 Balanoglossus is a burrowing worm like animal
 It is 12-18 inches long
 Found in the sandy shores
 It is divided into a proboscis, collar and trunk
 The mouth lies ventrally in a groove at the junction of
the proboscis and the collar
Feeding
 Its feeds on nutrients present in the mud
 Gill slits are present and they help in filtering off the
water taken in by the animal along with the food. Thus
they are called filter feeders
 They are omnivorous, devoid of biting structures and
swallow nutritive vegetative and animal matter present in
the soil.
 They have a ciliated skin
Respiration
 Water passes in by the mouth and out by the gill slits and
the respiratory exchange of gases takes place as the water
passes through the gill pouches
Defence Mechanisms
 The animal has a characteristic smell of iodoform that
keeps predators away from it
SUB PHYLUM UROCHORDATA OR TUNICATA
Ascidia
External Characters
 It is a free living tunicate
 The adult has a wrinkled cylinder/sac
 It is about 3-4 inches in length
 It has a broad base by which it attaches itself to rocks or
substrates
 It has a large aperture at its free end called the
mouth/inhalant siphon
 A little behind is the atrial/ exhalent aperture
 Water goes in through the mouth and out through the
atrial aperture
 When disturbed the animals squirts out water through the
atrial aperture and thus called a sea squirt
 The body is enclosed in a tough test or tunic composed
of tunicine (similar to cellulose)
 The test is attached to the body wall in the mouth region
and the atrial aperture and loose in the other places.
 The opening and closing of the mouth and the atrial
opening is regulated by the sphincter muscles
Body wall
 The body wall is found underlying the tunic and is
called the mantle
 It has an ectoderm which has connective tissue
containing blood vessels
Digestive system
 The mouth leads into the stomodeum and then opens into
the pharynx, which opens into the oesophagus followed
by the stomach, intestine and atrium which then opens
out by the anus (does not open directly out through the
anus like the invertebrates, there is an atrium)
 There is also a velum with a circlet of tentacles at the
junction of the stomodeum and pharynx
 The wall of the pharynx is perforated by numerous gill
slits
 These gill slits serve as the mode through which the
pharynx communicates with the atrial cavity
 On the ventral side of the pharynx is the endostyle which
secretes mucous.
 Food particles are carried into the mouth along with the
current by ciliary action
 The tentacles at the entrance of the pharynx serve as
strainer preventing coarse particles from entering into the
pharynx
 The mucous secreted by the glandular cells of the
endostyle, entangle the minute organisms into the
oesophagus
Respiratory System
 The pharyngeal region has blood vessels so that
exchange of gases takes place as the water passes in
and out
Blood Vascular System
 Muscular sac like heart is present close to the stomach.
 It is enclosed in a pericardium
 No definite vessels are seen
 The pulsation in the heart is peculiar, its shows a
periodical reversal of blood flow: ie. Blood is forced
forward during certain beats and backwards during
others
Excretion
 This is carried out by certain cells in the intestine
 No specialized ducts for removal of waste products are
seen
Nervous system
 Single nerve ganglion embedded in the mantle between
the mouth and atrial aperture is seen
Reproductive system
 They are hermaphrodites
 Testis and ovaries lies in the loop of the intestine
 Fertilization is external
 Fertilized ovum hatches and the larva is called an
ascidian tadpole
Affinities
 The ascidains are similar in their feeding type
 Presence of endostyle and atrium complexes
SUB-PHYLUM – CEPHALOCHORDATA
Branchiostoma lanceolatus/ Amphioxus lanceolatus
External Characters
 Commonly known as lancelet due to its shape
 It is a translucent animal about 1.5 – 2 inches long
 Found in shallow seas with sandy bottoms
 Look like a fish but differs in its structures and habitat
i.e. it has no distinct head, jaws, paired fins and no scales
Structure
 The body is long, pointed at both ends and compressed
 It has a dorsal fin, caudal fin and ventral fin
 The lateral edges of the body project out as two
longitudinal fin-like folds called the metapleural folds
 Below the anterior end of the body, there is a funnel
shaped cavity called the vestibule or stomodaeum
 This vestibule is surrounded by a membrane called the
oral hood which has numerous ciliated tentacles called
the buccal cirri
 Below the vestibule is the mouth which is fringed by
velar tentacles which are directed backwards into the
pharynx
 This movement causes the flow of water towards the
mouth and thus gives it a wheel like movement
appearance thus the tract is called the wheel organ.
These movement allow food to be taken into the mouth
 The anus lies a short distance in front of the hind end,
towards the left side of the ventral fin.
 It also has an atrium which surrounds the phayrnx, and
thus the coelom is greatly reduced due to the presence of
the atrium
Bodywall
 The body wall is covered by the epidermis, below which
is found the fibrous dermis. The two constitute the skin.
 Beneath the skin, is a muscular layer arranged
segmentally as muscle blocks called the myotomes.
 Myotomes are v-shaped and help during the sinus
movement of the organism
Skeleton
 Does not have a bone or cartilage but has notochordal
tissue and geleatinous materials
 It has a notochord- which is rod like and lies dorsally to
the alimentary canal and ventrally to the nerve cord
 It extends from one end to the other of the body
 This notochord is the forerunner of the vertebral column
in vertebrates
 Other skeletal structures include
Oral hood- is supported by a ring of small rods of
gelatinous material
Dorsal fin – has a single row of fin rays composed of
gelatinous materials
Ventral fin – has a double row of fin rays
Pharynx- is supported by gill bars which aid in
separating the gill slits
Digestive System
 The mouth leads into the pharynx
 The wall of the pharynx is perforated by numerous gill
slits on each side
 The pharynx then leads into the intestine or midgut
which extends backwards to open to the exterior by the
anus
 A blind diverticulum is given off on the right side of the
intestine called the hepatic caecum- which contains the
digestive enzymes
Feeding
 Amphioxus don’t move actively around for food but
usually buried in the sand
 Its oral end protrudes outside and feeds on small
organisms contained in the currents of water swept into
the mouth by the action of the cilia
 The cilia in the wheel organ and the gill bars of the
pharynx maintains the current of water flowing in and
out
 The velar tentacles strain off the coarse particles like
sand grains
 Small organisms are swept into the endostyle where the
mucous entangles them and the cilia drives them into the
intestine
 The water passes out by the gill slits
Vascular System
 The blood is colourless and no specialized heart is seen
Respiration
 Water enters through the pharynx which also serves
respiratory purpose
 The gills have blood vessels, hence as the water passes
between them, there is an exchange of gasses taking
place
Excretory System
 Excretory organs are paired nephridia. These are bent
tube with horizontal and vertical limb.
 The nephridium bears numerous branches ending blindly
in tufts of peculiar cells known as solenocytes
 Each solenocyte is a hollow cell with flagellum
 The nitrogenous waste pass through the walls of the
solenocytes
Nervous System
 The central nervous system has a nerve cord lying above
the notochord and below the fin rays
 No distinct brain is seen
 It has an olfactory pit whose function is olfaction
Reproduction
 Sexes are separate
 Gonads are simple sacs about 26 pairs arranged on each
side of the body wall
Affinities
Similar to the higher chordates
 Has notochord
 Nerve cord
 Gill slits
Differs from higher chordates
 No distinct head
 No specialized brain or organs associated with the head
like eyes, and auditory organs
 No distinct heart
 Excretion – nephridia- annelids
 Gonads are segmentally arranged with no ducts
 Body wall has myotomes
\
Invertebrate chordates provide clues to the origin of
vertebrates
A. Subphylum Urochordata
Species in the subphylum Urochordata are called tunicates.

Entire animal is cloaked in a tunic made of a celluloselike carbohydrate.

Most are sessile marine animals which adhere to rocks,
docks and boats.

Some species are planktonic, while others are colonial.
The tunicates are filter feeders.

Seawater enters through an incurrent siphon, passes
through the slits of the pharynx into a chambertcalled the
atrium, and exits via an excurrent siphon, the atriopore.

Food filtered from the water by a mucous net of the
pharynx is moved by cilia into the intestine.

The anus empties into the excurrent siphon.

When disturbed, tunicates eject a jet of water through
the excurrent siphon, so they are commonly called sea
squirts.
Adult tunicates bear little resemblance to other chordates.

They lack a notochord', a nerve cord and tail-

They possess only pharyngeal slits.
Larval tunicates are free swimmers and possess all four
chordate characteristics
Larva attach by the head on a surface and undergo
metamorphosis to adult form.
B. Subphylum Cephalochordata
Animals in the subphylum Cephalochordata are known as
lancelets due to their bladelike shape. Chordate characteristics
are prominent and persist in the adult. These include:

Notochord

Dorsal nerve cord

Numerous gill slits

Postanal tail
Cephalochordates are marine filter feeders.

They burrow tail first into the sand with only the anterior
exposed.

Water is drawn into mouth by ciliary action and food is
trapped on a mucous net secreted across the pharyngeal
slits.

Water exits through the slits and trapped food passes
down the digestive tube-
Cephalochordates are feeble swimmers with fishlike motions.

Frequently move to new locations

Muscle segments are serially arranged in chevron
like rows, and coordinated contraction flexes the
notochord from side to side in a sinusoidal pattern.

Muscle segments develop from blocks of mesoderm
called somites that are arranged along each side of the
notochord in the embryo.

The serial musculature is evidence of chordate
segmentation which developed independently of that in
annelids and arthropods.
C. Relationship of Invertebrate Chordates to the
Vertebrates
Vertebrates first appear in the fossil records in Cambrian
rocks.

Fossilized invertebrates {about 550 million years old)
resembling cephalochordates are found in Burgess Shale
of British Columbia.

This is about 50 million years older than the oldest
known vertebrates.
Most zoologists feel the vertebrate ancestors possessed all
four chordate characteristics and were suspension-feeders.

They may have resembled lance lets but were less
specialized.

Information provided by molecular systematics supports
the idea that cephalochordates are the closest relatives of
vertebrates.
Hemichordata Urochordata Cephalochordata
No trace of
Terminal anus.
notochord n
Blood flows
adult.
forward in
No nerve cord
dorsal blood
in adult.
Nonvessel.
Adult are
chordate
Pelagic larva
sessil filter
features
similar b
feeders,
holothurian
structurally
echinoderm
nothing like a
larva,
chordate
Fish-like animals
Chordate Tripartite body Gill slits in
Hemichordata Urochordata
features plan of preoral adult
proboscis,
multiplied to
collar and trunk form large
Pharyngeal slits filter-feeding
may have arisen pharynx.
initially to
Larva in
dispose of
ascidian
excess water
tadpole
created by
possesses the
feeding
following
mechanism.
features:
Laterly
notochord,
developed into pharyngeal
food-collecting slits, dorsal
device, e.g.
tubular nerve
Balanoglossus cord,
segmental
myotomes,
post-anal tail.
e.g,Ciona
Cephalochordata
showing all
recognisable
chordate features.
Notochord
extends length of
body in larval and
adult stages.
Large pharynx
with clefts forms
feeding
mechanism.
Ciliated gill bars.
Pharyngeal slits
open into atrium.
Segmental
myotomes.
No head or limbs.
e.g..Amphioxus
The evolution of vertebrate characteristics is associated
with increased size and activity
Vertebrates have retained the chordate features while adding
other specializations.
These features distinguish the vertebrates
from urochordates and cephalochordates.
The unique vertebrate structures probably evolved in
association with increased size and more active foraging for
food. The unique vertebrate adaptations include:

Vertebrates show a much greater degree
of cephalization than cephalochordates.
=> The brain and sense organs are located at the anterior
end which is the portion of the body which is in contact
with the most environmental stimuli.

A skeleton including a cranium and vertebral column is
the main axis of the body, replacing the notochord as the
basic skeleton.
=> The cranium protects the brain.
=> The vertebral column provides support and a strong,
jointed anchor that provides leverage to the segmental
swimming muscles.
=> The axial skeleton made larger size and stronger,
faster movement possible.
=> Most vertebrates also have ribs (anchor muscles and
protect internal organs) and an appendicular skeleton
supporting two pairs of appendages.

The vertebrate skeleton may be composed of bone,
cartilage, or a combination of the two.
=> A majority of the skeleton is a non-living matrix
which is secreted and maintained by living skeletal cells.
=> The living vertebrate endoskeleton can grow with the
animal unlike the exoskeleton of arthropods.

The neural crest, a group of embryonic cells found only
in vertebrates, contributes to the formation of certain
skeletal components and many other structures
distinguishing vertebrates from other chordates.
=> The dorsal, hollow nerve cord develops from
an infolding of the edges of an ectodermal plate on the
surface of the embryo.
=> The neural crest forms near the dorsal margins of the
tube resulting from this
infolding.
=> Cells from the neural crest then migrate to various
specific areas of the embryo and help form a variety of
structures including some of the bones and cartilage of
the head.
Some anatomical adaptations also support the greater
metabolic demands of increased activity .

The generation of A TP by cellular respiration, to replace
the energy used by vertebrates in obtaining food or
escaping predators, consumes oxygen.
=> The respiratory and circulatory systems of vertebrates
show adaptations which support the mitochondria of
muscles and other active tissues.

Vertebrates have a closed circulatory system composed
of a ventral chambered (2 to 4) heart, arteries, capillaries
and veins.
=> The heart pumps the blood through the system.
=>The blood becomes oxygenated as it passes through
the capillaries of the gills or lungs.

The more active the life style, the larger the amounts of
organic molecules necessary to produce energy.
=> Vertebrates have several adaptations for feeding,
digestion and nutrient absorption.
=> For example, muscles in the walls of the digestive
tract move food from organ to organ along the tract.