phylum-chordata-and-protochordates in diversity of chordates

chordata in detail is described in this ppt

1. PHYLUM CHORDATA
(Protochordates)
INTRODUCTION, CLASSIFICATION
AND GENERAL CHARACTERS OF
CHORDATES AND
PROTOCHORDATES

2. 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.

3. In the scheme of classification, the Animal Kingdom is divided first into
several major animal groups called phyla (singular, phylum). There are
approximately 30 animal phyla currently recognised. The last major group of
the Animal Kingdom is known as phylum Chordata.
 It was created by Balfour in 1880. The name of this phylum is derived from
two Greek words, the “chorde” meaning a string or cord, and “ata” meaning
bearing. The reference is to a common characteristic feature in the form of a
stiff, supporting rod-like structure along the back, the which is found in all
the members of the phylum at some stage of their lives.
Thus, chordates are animals having a cord, i.e., notochord. The animals
belonging to all other phyla of the Animal Kingdom are often termed 'the
non-chordates' or 'the invertebrates since they have no notochord or
backbone in their body structure.

4. 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.

5. 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

6. 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.

7. DIAGRAM OF NOTOCHORD

8. Notochord or chorda dorsalis. The notochord
is an elongated rod-like flexible structure
extending the length of the body. It is present
immediately beneath the nerve cord and just
above the digestive canal. It originates from
the endodermal roof of the embryonic
archenteron. Structurally, it is composed of
large vacuolated Protochordates have a
typical notochord. In adult vertebrates, it is
surrounded or replaced by the vertebral
column.

9. 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.

10. FIGURE 1: A generalized chordate showing fundamental
chordate characters

11. 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.

12. Dorsal hollow nerve cord.
The central nervous system of the chordates is present dorsally in
the body. It is in the form of a longitudinal, hollow or tubular nerve
cord lying just above the notochord and extending lengthwise in the
body. The nerve cord or neural tube is derived from the dorsal
ectodermal neural plate of the embryo and encloses a cavity or
canal called neurocoel. There are no distinct ganglionic
enlargements. The nerve cord serves for the integration and
coordination of the body activities. In vertebrates, the anterior region
of nerve cord is specialized to form a cerebral vesicle or brain which
is enclosed by a protective bony or cartilaginous cranium. The
posterior part of nerve cord becomes the spinal cord and protected
within the vertebral column.

13. 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.

14. 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)

15. Pharyngeal gill slits. In all the chordates, at some stage of their life
history, a series of paired lateral gill clefts or gill slits perforate
through the pharyngeal wall of the gut behind the mouth. These are
variously termed as pharyngeal, branchial and visceral clefts or
pouches. They serve primarily for the passage of water from the
pharynx to outside, thus bathing the gills for respiration. The water
current secondarily aids in filter feeding by retaining food particles in
the pharynx. In protochordates (e.g. Bronchia stoma) and lower
aquatic vertebrates, the gill slits are functional throughout life. But, in
higher vertebrates, they disappear or become modified in the adult
with the acquisition of pulmonary respiration.

16. 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.

17. The above three common features appear during early embryonic
life of all the chordates.But all the three features rarely persist in the
adult (e.g. Brcmchiostoma). Often they are modified or even lost in
the adult stages of higher chordates. The notochord disappears
during development in most vertebrates, while the nerve cord and
the pharyngeal clefts or their derivatives remain in the adult. The
three common chordate characters were probably characteristic of
the ancestral chordates. They distinguish chordates from all other
animals and appear to reveal their common ancestry.

18. 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.

19. 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

20. CLASSIFICATION OF
CHORDATES
PHYLUM
CHORDATA
GROUP 1
ACRANIATA
GROUP 2
CRANIATA
SUB –PHYLUM
UROCHORDATA
SUB- PHYLUM
CEPHALOCHORDATA
SUB-PHYLUM
AGNATHA
SUB-PHYLUM
GNATHOSTOMATA

21. 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)

22. 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 "tail-
cord").
 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.

23. FIGURE: 2 Tunicates: sea squirts

24. 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 in-
current 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)

25. 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.

26. 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.

27. 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.

28. 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.

29. FIGURE 4: LARVAL AND ADULT ASCIDIAN
Ascidian Larvae
Young Ascidian
Larvae
Older Ascidian Larvae
Adult Ascidian

30. 2-SUB-PHYLUM
CEPHALOCHORDATA
DEFINATION:
Cephalochordates are small, eel-
like 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.

31. 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)

32. FIGURE 5: AMPHIOXOUS

33. 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)

34. FIGURE 6: AMPHIOXOUS INTERNAL STRUCTURE

35. More about cephalochordates
RESPIRATION: Respiration through the
general body surface. No special organ for
respiration.
CIRCULATORY SYSTEM:
Cephalochordates also have a well-
developed circulatory system.
EXCRETORY SYSTEM: Simple excretory
system composed of paired nephridia.

36. 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.