D.N.R.COLLEGE (A), BHIMAVARAM
Department of Zoology
Study material
Semester II
Animal Diversity- Biology of Chordates
0
, ANIMAL DIVERSITY OF CHORDATES – CYCLOSTOMATA & PISCES
UNIT-1
LONG ANSWER QUESTIONS
1A1.Define Chordata. Give an account of general characters of
Chordates.
Phylum chordata is the largest group of Deuterostomes. Blastopore develop into
Anus during embryonic development. Most of the present day Chordates are
familiar vertebrates like fishes, amphibians,reptiles,birds and mammals besides
marine mammals like Dolphins and Whales. Nearly 49,000 species of chordates are
recorded.
Distribution: Chordates are found in the marine waters, fresh water and in the air.
Birds and mammals could go and live in the cold climate because they have a
constant body temperature (stenothermic).
Important fundamental Chordate Characters:
(1) Notochord
(2) Dorsal tubular nerve cord
(3) Pharyngeal gill slits
(4) Post anal tail
Notochord or chorda dorsalis:
It develops from the Endodermal layer of embryonic archenteron.
It consists of large vacuolated notochord cells containing gelatinous matrix.
It is surrounded by outer fibrous sheath and inner elastic sheath.
Notochord is present as an elongated rod-like, flexible structure running all
along the length of the animal.
1
, ANIMAL DIVERSITY OF CHORDATES – CYCLOSTOMATA & PISCES
It is situated immediately below the nerve cord and just above the alimentary
canal.
The notochord serves as a supporting internal skeleton which differs with the
nerve cord both in its structure and function.
In Protochordates it is present even in adults but in higher vertebrates it is
replaced by vertebral column. Presence of notochord is a fundamental
chordate character.
Dorsal Nerve cord:
Dorsal nerve cord represents the central nervous system of the chordates.
The nerve cord is a hollow tubular structure which is parallel to the
notochord and present above it.
The hollow cavity of the cord is called as Neurocoel which is derived from
the ectodermal neural plate of the embryo. The main function of the nerve
cord is to maintain the integration and co ordination of activities of an
animal.
In chordates (Vertebrates) the anterior part of the nerve cord enlarges into a
vesicle which forms the brain and the posterior part becomes the spinal cord
in the adult, enclosed within the Vertebral column.
Pharyngeal gill slits:
In all chordates during their developmental stages, just behind the mouth
in the pharyngeal wall, series of lateral gill slits or gill clefts are formed
and they are termed or named as pharyngeal, branchial and visceral clefts
or pouches.
These structures help in passing out of water from pharynx over the
external gills to outside. The water current also helps in filter feeding of
the by filtering food particles present in water.
In protochordates and in all fishes the gill slits are persistent or remain
throughout the life carrying aquatic or gill respiration. In higher
vertebrates they disappear during developmental stages and modified to
acquire pulmonary respiration.
During early embryonic life of all chordates the above said three
characters are present. These characters are rarely persist in the adult
chordates (e.g., Branchiostoma) and either modified or lost in the adult
stage.
In many chordates the notochord disappear but the nerve cord and the
pharyngeal clefts remain in the adult.
2
, ANIMAL DIVERSITY OF CHORDATES – CYCLOSTOMATA & PISCES
Post anal tail:
It is an extension of the body to the anus. In chordates, the tail is composed
of skeletal muscles which help in locomotion in fish-like species. It is absent in
most of the adult Chordates.
Other characteristics of chordates include
1. Bilaterally symmetrical, triploblastic, coelomic and segmented body.
2. The body design is complex and well-differentiated.
3. The body has an organ system level of organization.
GENERAL CHARACTERISTICS
Aquatic, aerial or terrestrial all free living with no fully parasitic forms.
Bilaterally symmetrical and metamerically segmented.
Exoskeleton often present well developed in most vertebrates.
Bodywall triploblastic with 3 germinal layers: ectoderm, mesoderm and
endoderm.
Coelomate animals with a true coelom, enterocoelic or schizocoelic in
origin.
A skeletal rod, the notochord, present at some stage in life cycle.
Digestive system complete with digestive glands.
Blood vascular system closed. Heart ventral with dorsal and ventral blood
vessels. Hepatic portal system well developed.
Excretory system comprising proto –or meso-or meta-nephric kidneys.
1A2.List out general characters of Cephalochordates.
Cephalochordates are also called as lancelets (Branchiostoma) - Amphioxus is the
sole representative of the subphylum Cephalochordata.
These are slender, laterally compressed and translucent animals about 5 to 7
cm in length. There are about two dozen species of this genus found
distributed all over the world.
Surface of the body has V-shaped myotomes visible externally.
It burrows in sand and spends most of its time buried tail down in sand with
only its head including the mouth exposed above the surface. During
breeding season it usually comes out of sand at night and swims.
It feeds upon organic particles and small plankton which are brought to the
mouth by the inhalant current of water.
During feeding, the cilia lining the oral funnel create an inhalant current.
Water is then drawn into the mouth through a membranous velum which
bears twelve short tentacles.
3
Department of Zoology
Study material
Semester II
Animal Diversity- Biology of Chordates
0
, ANIMAL DIVERSITY OF CHORDATES – CYCLOSTOMATA & PISCES
UNIT-1
LONG ANSWER QUESTIONS
1A1.Define Chordata. Give an account of general characters of
Chordates.
Phylum chordata is the largest group of Deuterostomes. Blastopore develop into
Anus during embryonic development. Most of the present day Chordates are
familiar vertebrates like fishes, amphibians,reptiles,birds and mammals besides
marine mammals like Dolphins and Whales. Nearly 49,000 species of chordates are
recorded.
Distribution: Chordates are found in the marine waters, fresh water and in the air.
Birds and mammals could go and live in the cold climate because they have a
constant body temperature (stenothermic).
Important fundamental Chordate Characters:
(1) Notochord
(2) Dorsal tubular nerve cord
(3) Pharyngeal gill slits
(4) Post anal tail
Notochord or chorda dorsalis:
It develops from the Endodermal layer of embryonic archenteron.
It consists of large vacuolated notochord cells containing gelatinous matrix.
It is surrounded by outer fibrous sheath and inner elastic sheath.
Notochord is present as an elongated rod-like, flexible structure running all
along the length of the animal.
1
, ANIMAL DIVERSITY OF CHORDATES – CYCLOSTOMATA & PISCES
It is situated immediately below the nerve cord and just above the alimentary
canal.
The notochord serves as a supporting internal skeleton which differs with the
nerve cord both in its structure and function.
In Protochordates it is present even in adults but in higher vertebrates it is
replaced by vertebral column. Presence of notochord is a fundamental
chordate character.
Dorsal Nerve cord:
Dorsal nerve cord represents the central nervous system of the chordates.
The nerve cord is a hollow tubular structure which is parallel to the
notochord and present above it.
The hollow cavity of the cord is called as Neurocoel which is derived from
the ectodermal neural plate of the embryo. The main function of the nerve
cord is to maintain the integration and co ordination of activities of an
animal.
In chordates (Vertebrates) the anterior part of the nerve cord enlarges into a
vesicle which forms the brain and the posterior part becomes the spinal cord
in the adult, enclosed within the Vertebral column.
Pharyngeal gill slits:
In all chordates during their developmental stages, just behind the mouth
in the pharyngeal wall, series of lateral gill slits or gill clefts are formed
and they are termed or named as pharyngeal, branchial and visceral clefts
or pouches.
These structures help in passing out of water from pharynx over the
external gills to outside. The water current also helps in filter feeding of
the by filtering food particles present in water.
In protochordates and in all fishes the gill slits are persistent or remain
throughout the life carrying aquatic or gill respiration. In higher
vertebrates they disappear during developmental stages and modified to
acquire pulmonary respiration.
During early embryonic life of all chordates the above said three
characters are present. These characters are rarely persist in the adult
chordates (e.g., Branchiostoma) and either modified or lost in the adult
stage.
In many chordates the notochord disappear but the nerve cord and the
pharyngeal clefts remain in the adult.
2
, ANIMAL DIVERSITY OF CHORDATES – CYCLOSTOMATA & PISCES
Post anal tail:
It is an extension of the body to the anus. In chordates, the tail is composed
of skeletal muscles which help in locomotion in fish-like species. It is absent in
most of the adult Chordates.
Other characteristics of chordates include
1. Bilaterally symmetrical, triploblastic, coelomic and segmented body.
2. The body design is complex and well-differentiated.
3. The body has an organ system level of organization.
GENERAL CHARACTERISTICS
Aquatic, aerial or terrestrial all free living with no fully parasitic forms.
Bilaterally symmetrical and metamerically segmented.
Exoskeleton often present well developed in most vertebrates.
Bodywall triploblastic with 3 germinal layers: ectoderm, mesoderm and
endoderm.
Coelomate animals with a true coelom, enterocoelic or schizocoelic in
origin.
A skeletal rod, the notochord, present at some stage in life cycle.
Digestive system complete with digestive glands.
Blood vascular system closed. Heart ventral with dorsal and ventral blood
vessels. Hepatic portal system well developed.
Excretory system comprising proto –or meso-or meta-nephric kidneys.
1A2.List out general characters of Cephalochordates.
Cephalochordates are also called as lancelets (Branchiostoma) - Amphioxus is the
sole representative of the subphylum Cephalochordata.
These are slender, laterally compressed and translucent animals about 5 to 7
cm in length. There are about two dozen species of this genus found
distributed all over the world.
Surface of the body has V-shaped myotomes visible externally.
It burrows in sand and spends most of its time buried tail down in sand with
only its head including the mouth exposed above the surface. During
breeding season it usually comes out of sand at night and swims.
It feeds upon organic particles and small plankton which are brought to the
mouth by the inhalant current of water.
During feeding, the cilia lining the oral funnel create an inhalant current.
Water is then drawn into the mouth through a membranous velum which
bears twelve short tentacles.
3
