The chordates are named for the notochord: a flexible, rod-shaped structure that is found in the embryonic stage of all chordates and also in the adult stage of some chordate species.
It is located between the digestive tube and the nerve cord, providing skeletal support through the length of the body.
In some chordates, the notochord acts as the primary axial support of the body throughout the animal's lifetime.
2. Characteristics of Phylum Chordata
1. A notochord
2. A dorsal hollow nerve cord
3. Pharyngeal slits
4. Post-anal tail
3. Notochord
The chordates are named for the notochord: a flexible, rod-
shaped structure that is found in the embryonic stage of all
chordates and also in the adult stage of some
chordate species.
It is located between the digestive tube and the nerve cord,
providing skeletal support through the length of the body.
In some chordates, the notochord acts as the primary axial
support of the body throughout the animal's lifetime.
4. In vertebrates, the notochord is present during
embryonic development, at which time it induces the
development of the neural tube which serves as a
support for the developing embryonic body.
The notochord, however, is replaced by the vertebral
column (spine) in most adult vertebrates.
5. Dorsal Hollow Nerve Cord
The dorsal hollow nerve cord derives from ectoderm that
rolls into a hollow tube during development.
In chordates, it is located dorsally (at the top of the
animal) to the notochord.
In contrast to the chordates, other animal phyla are
characterized by solid nerve cords that are located either
ventrally or laterally.
The nerve cord found in most chordate embryos develops
into the brain and spinal cord, which comprise the
central nervous system.
6.
7. Pharyngeal Slits
Pharyngeal slits are openings in the pharynx (the region
just posterior to the mouth) that extend to the outside
environment.
In organisms that live in aquatic
environments, pharyngeal slits allow
for the exit of water that enters the
mouth during feeding.
Some invertebrate chordates use the pharyngeal slits to
filter food out of the water that enters the mouth.
In vertebrate fishes, the pharyngeal slits develop into gill
arches, the bony or cartilaginous gill supports.
8. In most terrestrial animals, including mammals and
birds, pharyngeal slits are present only during
embryonic development.
In these animals, the pharyngeal slits develop into
the jaw and inner ear bones.
9. Post-Anal Tail
The post-anal tail is a posterior elongation of the body,
extending beyond the anus.
The tail contains skeletal elements and muscles, which
provide a source of locomotion in aquatic species.
In some terrestrial vertebrates, the tail also helps with
balance, courting, and signaling when danger is near.
In humans and other apes, the post-anal tail is present
during embryonic development, but is vestigial as an adult.
13. Protochordata
They are primitive chordates without head and
vertebral column.
Subphylum are as follows :-
1. UROCHORDATA- sedentary or planktonic
tunicates in which chordate characters manifest in
the larval stage. Eg: Herdmania, Salpa, Doliolum,
Pyrosoma, Oikopleura
2. CEPHALOCHORDATA- typical chordates having
chordate characters in the larval as well as adult
stage. Eg: Amphioxus, Asymmetron
14. Euchordata
They are true chordates.
Subphylum include vertebrata
Superclass are as follows :-
1. AGNATHA
2. GNATHOSTOMATA
15. Agnatha
It includes 90 species of paraphyletic group of
jawless fishes, which were also the first vertebrates.
Living forms are elongated, scaleless, slimy parasites
and scavengers that include lampreys and hagfishes.
They have no paired fins.
Class:-
16. 1. OSTRACODERMI- extinct shelled jawless fishes of
Ordovician period. Eg: Cephalaspsis
2. CYCLOSTOMATA- jawless fishes of today, without
scales and paired fins. Eg: Myxine, Bdellostoma,
Petromyzon
17. Gnathostomata
It includes vertebrates with jaws and have modified
gill arches and paired appendages.
They include pisces and tetrapods.
18. Fishes
A fish is any member of a paraphyletic group of organisms that consist
of all gill-bearing aquatic craniate animals that lack limbs with digits.
Class includes :-
1. CHONDRICHTHYES – cartilaginous fishes that have cartilaginous
skeleton, ventral mouth, placoid scales, heterocercal tail fin and 5
pairs of gill slits. Eg: Chimaeras
2. OSTEICHTHYES – 20,000 species, bony fishes. Skeleton contains
bone, four pairs of gills, covered with operculum. Possess swim
bladder or lungs. Eg: Tuna, eel
19.
20. TETRAPODS
Comprises the four-limbed vertebrates and their
descendants.
Class include :-
1. Class AMPHIBIA- Eg: Frog, Salamander
2. Class REPTILIA- Snake, Turtle
3. Class AVES- Eg: Owl, Eagle
4. Class MAMMALIA- Eg: Human, Lion
A flexible rodlike structure that forms the main support of the body in the lowest chordates; a primitive spine
The series of vertebrae, separated by disks, that encloses and protects the spinal cord, and runs down the middle of the back in vertebrate animals.
In humans, the first pair of pouches becomes the tonsils, while the third and fourth pairs become the thymus and parathyroid glands.
Embryologist and evolutionist Michael Richardson and colleagues dropped a bomb on Haeckel's long-held concept known as "embryonic recapitulation." He compared Haeckel's old drawings with actual photographs of the same embryos in a 1997 technical paper.1 The comparison showed that Haeckel's drawings were frauds.
Tuinicate :a marine invertebrate of a group which includes the sea squirts and salps. They have a rubbery or hard outer coat and two siphons to draw water into and out of the body.
Paraphyletic: descended from a common evolutionary ancestor or ancestral group, but not including all the descendant groups.
The Ordovician Period lasted almost 45 million years, beginning 488.3 million years ago and ending 443.7 million years ago.
) tooth-like, being made of dentine with a pointed backward projection of enamel, as in sharks and rays.
Heteroceral having unequal upper and lower lobes, usually with the vertebral column passing into the upper.