Download Chapter 2 SEM II Phylum Chordata Phylum chordate includes

Chapter 2
SEM II Phylum Chordata
Phylum chordate includes animals exhibiting diverse habits, forms and
structure.
Prime features or characteristics of phylum chordates: Following are the
three prime characters that are seen present only in chordates. Of these three
mentioned characters, any two should be present in either embryonic/larval or
adult stage in the life-cycle of organism
1. Presence of Notochord(Gr noton-back, chordae- cord): It is also called
as Chorda-dorsalis. It is solid ,dorsal, tubular rod present between
nerve cord and alimentary canal.It is composed of vacuolated cells
enclosed in notochordal sheath.In lower chordates notochord persist
throughout its life cycle but in higher groups it is replaced partially or
completely by vertebral column.
2. Presence of Nerve cord: It is dorsal, hollow, non-ganglionated tubular
nerve cord present along mid-dorsal line above notochord. It persists
throughout life in all chordates. It gets differentiated into anterior brain
and posterior spinal cord.
3. Presence of pharyngeal gill slits or gill clefts: These are paired lateral
opening in the lateral wall of the pharynx in almost all chordates in their
embryonic stage.
General characters /salient features of Chordates:
1. Habit and Habitat: They are social, colonial or solitary in nature
showing aquatic, arboreal, aerial or terrestrial mode of living.
2. Germ layers: Chordates are triploblastic in nature comprising of three
germ layers-ectoderm, mesoderm and endoderm.
3. Coelom : All chordates possess true coleom and thus are called
eucoelomates. It develops from primitive gut thus called enterocoel and
later get differentiated as abdominal cavity around abdominal viscera,
pleural cavity around lungs and pericardial cavity around heart.
4. Body plan: All chordates have tube with- in- a- tube type of body plan.
5. Organization: they exhibit organ grade of organization.
6. Symmetry: Chordates show bilateral symmetry.
7. Metamerism/: Chordates show metameric segmentation which is less
prominent externally .It is mainly evident in the internal structure like
kidney tubules, spinal nerve.
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8. Cephalization: Few of the anterior segments are fused and gets
differentiated to form head bearing mouth, brain and sense organs.
9. Appendages: Appendages are unpaired in lower chordates, both paired
and unpaired in fishes and only paired in tetrapods. Some tetrapods
show presence of tail as balancing organ.
10. Digestive system: It is complete and show presence of both
intracellular and extracellular digestion. Many digestive glands are
present.
11. Respiratory system: Respiration is either with the help of gills (Gill
respiration), skin (Cutaneous respiration) or lungs (pulmonary
respiration).
12. Circulatory system: Closed circulation is well developed in all
chordates. It consist of pulsating organ-heart and blood vessels namely
artery and vein.
13. Blood: It is red in color due to presence of respiratory pigmenthaemoglobin
a. Direction of blood flow: Blood flows in forwards direction in ventral
vessels and backwards in dorsal vessels.
b. Portal system: Three portal systems are present in chordates
namely
i. Hepatic portal system
ii. Renal portal system and
iii. Hypothalamo-hypophysial portal system (in man).
14. Excretory system: A pair of excretory kidney, ureter and urethra forms
excretory system in chordates. Depending of the nature of excretion of
nitrogenous waste these organism are classified as
i. Ammontelic: These organisms excretes ammonia as their
excretory waste.
ii. Uricotelic: These organisms excrete urea as their excretory waste.
iii. Uriotelic : These organisms excretes uric acid as their excretory
waste.
15. Skeleton system; Both endoskeleton and exoskeleton is well developed
in chordates
a. Endoskeleton: Endoskeleton is in the form of bones and cartilage.
b. Exoskeleton: Exoskeleton is in form of scales, feathers, fur, hair,
hooves, nails, horns .
16. Endocrine system: It is present in all chordates, which helps in
bringing co-ordination of body.
17. Nervous system: All chordates possess well developed nervous system.
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18. Reproductive system: Chordates show sexual reproduction. Some of
them are
a. Oviparous: Egg laying organism
b. Viviparous: Giving birth to young ones which are exactly similar to
adult in all forms except mature reproductive system.
19. Development: Organism show direct development which is of
following types
a. Placenta: During early development young one show adherence with
maternal tissue and it imparts protection and provides nourishment
to developing embryo through placenta. Ex. primates
b. Pouched: Some animals like Kangaroo show early development in
pouch outside the body.
CLASSIFICATION
Phylum Chordata
Group
Acraniata/Protochordata
(G.A-Absence; Cranium- Brain box)
(G.Protos- first/Primitive)
Craniata
(G. Cranium- Brain box)
Phylum chordate is divided into following two Divisions and three subphylum
A. Group–Acraniata (G. A-Absence , Cranium-brain box)
1. Absence of cranium, vertebra and paired fins is prime character of
this group.
2. Blood is colourless.
3. Paired organs for hearing and eyes.
4. Epidermis is single layered.
5. Peribranchial cavity present.
6. It is also called as Protochordata(G.Proto-First/primitive)
Group Acraniata includes two subphylum
a. Subphylum -Urochordata: (Gr. Auro- Tail; chorde-cord): The
notochord is present only in the tail region of the larva.
Ex. Primitive chordates like Herdmania commonly called Seasquint.
b. Subphylum -Cephalochordata: (Gr Cephalous-Head) The
notochord is well developed and extends from anterior to posterior
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region and extends beyond the nerve cord. Hence they are commonly
called cephalochordate. Ex. Amphioxus
B. Group-Craniata (G. Cranium-brain box):It includes higher vertebrates
1. Presence of Cranium, vertebrata and paired limbs and girdles are
prime characters of this group.
2. Blood is coloured.
3. Paired organs for hearing and sight.
4. Epidermis many layered(straitified)
5. No peribrachial cavity.
Group Craniata includes subphylum
a. Subphylum -Vertebrata: Notochord is replaced by vertebral
column
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