Download Phylum chordata and protochordates

PRESENTED AND
PREPARED BY
SADIA KHURSHID
LECTURER ZOOLOGY DEPARTMENT
DA COLLEGE FOR WOMEN,PHASE VIII
PHYLUM CHORDATA
(Protochordates)
INTRODUCTION, CLASSIFICATION
AND GENERAL CHARACTERS OF
CHORDATES AND
PROTOCHORDATES
OUTLINE
Definition
Fundamental
characters
General characters
Classification of chordata
Group Acraniata
UROCHORDATA
More details
Systems
CEPHALOCHORDATA
SYSTEM
DEFINATION
The name of this phylum is derived
from two Greek words, the chorde
meaning a string or cord, and ata
meaning bearing, group or forms.
Thus chordates are animals
having a cord , i.e., notochord.
CHORDATES
They include about 45000species
including many animals of major
economic importance.
 Phylum Chordata includes the most
highly evolved animals, the
vertebrates, as well as the marine
invertebrate cephalochordate,
amphioxus and tunicates.

FUNDAMENTAL CHARACTERISTICS
OF CHORDATES
All chordates shows all or at least
any one of the following three
fundamental characteristics:
 Notochord
 Nerve
cord
 Pharyngeal gill slits
1-NOTOCHORD(chorda dorsalis)
DEFINATION:
The notochord is an elongated,
flexible cartilaginous rod-like,
skeletal structure lies dorsal to
the gut tube and ventral to the
nerve cord.
DIAGRAM OF NOTOCHORD
Fates of notochord
In most adult chordates the notochord
disappears or becomes highly modified, or
it is surrounded and replaced by a vertebral
column.
In some non-vertebrate chordates and
fishes the notochord persists as a laterally
flexible but incompressible skeletal rod.
FIGURE 1: A generalized chordate showing fundamental
chordate characters
2-NERVE CORD
DEFINATION:
The nerve cord of chordates
develops dorsally in the body
as longitudinal, a fluid filled
hollow tube, lying just above
the notochord and extending
lengthwise in the body.
Fates of nerve cord
In most species it differentiates in
embryogeny into the brain anteriorly
and spinal cord that runs through
the trunk and tail. Together the brain
and spinal cord are the central
nervous system to which peripheral
sensory and motor nerves connect.
3-PHARYNGEAL GILL SLITS
DEFINATION:
In all chordates, at some stages of their life history, a
series of paired lateral gill cleft or gill slits perforate
through the pharyngeal wall of the gut behind the
mouth. These are variously termed as branchial,
visceral or pharyngeal cleft or pouches.
The soft and skeletal tissues between adjacent
clefts are the visceral arches. (FIGURE. 1)
Function of gill cleft
 Gill
cleft serve primarily for the
passage of water from the pharynx
to outside , thus bathing the gills
for respiration.
 The water current secondarily aid
in filter feeding by retaining food
particles in the pharynx.
Embryonic fate of the clefts
Non-vertebrate chordates: The clefts and arches
are elaborated as straining devices concerned
with capture of small food particles from water
and are function throughout life.
Fish-like vertebrates and juvenile amphibians : The
walls of the pharyngeal clefts develop into gills
that are organs of gas exchange between the
water and blood.
Adult amphibians and the amniotes tetrapods: The
anterior most cleft transforms into the auditory
tube and middle ear chamber, whereas the other
clefts disappear after making some important
contributions to glands lymphatic tissue in the
throat region.
GENERAL CHARACTERISTICS OF
CHORDATES
Chordates in general have following
characteristics:
 Bilateral symmetry
 Triploblastic
 Deuterostome
 Complete digestive tract
 Well developed coelom
 Internal organs are suspended in the coelomic
cavity by a thin membranous tissue called
mesentery
 Sexual reproduction
 Post anal tail
CLASSIFICATION OF
CHORDATES
PHYLUM
CHORDATA
GROUP 1
ACRANIATA
SUB –PHYLUM
UROCHORDATA
GROUP 2
CRANIATA
SUB- PHYLUM
CEPHALOCHORDATA
SUB-PHYLUM
AGNATHA
SUB-PHYLUM
GNATHOSTOMATA
1-Group ACRANIATA
(Protochordata)




They are the simple or first chordates in which
brain box (cranium) is absent and hence brain is
not prominent.
Notochord does not transform into vertebral
column.
Group acraniata is divided into two sub
phylum:
Urochordata (notochord in the tail)
Sub-phylum cepalochordata (notochord from
head to tail)
1-SUB-PHYLUM UROCHORDATA
(Tunicata)


Urochordates have a notochord that extends
from just behind the head to the tail (rather than
from head to tail; Urochordata means "tailcord").
Urochordates are also called tunicate because
their body is enclosed in a sac called tunic or
test composed largely of tunicine, similar to
cellulose. (FIGURE-2) Tunicate includes about
2,000 fixed and nearly 100 pelagic species.
FIGURE: 2 Tunicates: sea squirts
More about Urochordates

DIGESTIVE SYSTEM:They are all marine and sessile. Most
tunicates feed by filtering sea water through pharyngeal
slits.Tunicates are suspension feeders. They have two openings in
their body cavity, an in-current and an ex-current siphon. The incurrent siphon is used to intake food and water, and the ex-current
siphon expels waste and water.

The tunicate's primary food source is plankton. Plankton gets
entangled in the mucus secreted from the endostyle.The tunicate's
pharynx is covered by miniature hairs called ciliate cells which
allow the consumed plankton to pass down through to the
esophagus. Their gut is U-shaped, and their anuses empty directly
to the outside environment. They have complete digestive
tract.(FIGURE-3)
Figure 3: Internal organs of adult ascidians (sea squirt). Large
arrows show water flow through the animal; small arrows, the path
food trapped by the pharyngeal gill slits takes through the animal.
RESPIRATION, EXCRETION
AND COELOM



RESPIRATION: They have two to seven
pairs of gill slits. Respiration through test and
gill slits.
EXCRETION: Tunicates lack the kidney-like
metanephridial organs. They have neural
gland, pyloric gland and nephrocytes.
COELOM: The original coelom body-cavity
develops into a pericardial cavity and gonads.
What the Urohordates have?
Like other chordates, tunicates have a
notochord during their early development,
but lack myomeric segmentation
throughout the body and tail as adults.
Blood vascular system:Blood vascular
system is of open type. Heart is simple,
ventral and tubular. Tunicate blood
contains high concentrations of the metal
vanadium ,vanadium-associated proteins
as well as lithium.
REPRODUCTION



Most tunicates are hermaphrodites. Tunicates begin
life in a mobile larval stage that resembles a tadpole,
and exhibit chordates characters. It contains a nerve
cord and a short notochord in its tail only .
As the larva reaches maturity it attaches to the sea
bottom and undergoes retrogressive metamorphosis
by losing its tail and most of the chordate
characters.only gill slits persist. Later, it develops into
a barrel-like and usually sedentary adult form.
(FIGURE-4)
IN PAKISTAN:
Many species of Herdmania are fond in our seas.
FIGURE 4: LARVAL AND ADULT ASCIDIAN
Ascidian Larvae
Adult Ascidian
Young Ascidian
Larvae
Older Ascidian Larvae
2-SUB-PHYLUM
CEPHALOCHORDATA
DEFINATION:
Cephalochordates are small, eellike animals that spend much of
their time buried in sand. They
have notochord and nerve cord
extends from head up to the tail,
and persists throughout life.
Chordates features
Cephalochordates have all the typical chordate features.
 dorsal nerve cord
 notochord.
 pharyngeal slits (100 )which are used to strain food
particles out of the water.
 The musculature of the body is divided up into V-shaped
blocks, or myomeres.
 post-anal tail.
 On the other hand, cephalochordates lack features
found in most or all true vertebrates, small brain and
poorly developed sense organs and no true vertebrae.
(FIGURE-5)
FIGURE 5: AMPHIOXOUS
DIGESTIVE SYSTEM:
Digestive tract is complete. Pharynx is
large perforated by numerous gill slits.
They are filter feeder.
A pouch or hepatic caecum secretes
digestive enzymes, and actual digestion
takes place in a specialized part of the
intestine known as the iliocolonic ring.
(FIGURE -6)
FIGURE 6: AMPHIOXOUS INTERNAL STRUCTURE
More about cephalochordates



RESPIRATION: Respiration through the
general body surface. No special organ for
respiration.
CIRCULATORY SYSTEM:
Cephalochordates also have a welldeveloped circulatory system.
EXCRETORY SYSTEM: Simple excretory
system composed of paired nephridia.
REPRDUCTION
Reproduction is sexual. The sexes
are separate, and both males and
females have multiple paired gonads.
Eggs are fertilized externally, and
develop into free-swimming, fishlike
larvae. No asexual reproduction.
Development is indirect.
SPECIES NUMBERS
Cephalochordates comprises about 30
species.
IN PAKISTAN:
Out of only two genera found around the
world, Branchiostoma is found on our coast.
REFERENCES
WEBSITE USED:
 www.wikipedia.com
 www.youtube.com
 www.google.com
 www.glossary.com
 www.answer.com
BOOKS:
 Elements of Chordate Anatomy by Charles K. Weichert
 Modern Text Book of Zoology, Vertebrates. R.L. Kotpal
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