Phylum Chordata: Notes and MCQs for NEET UG

Introduction

Animals in the phylum Chordata are distinguished by three primary features: the presence of a notochord, a dorsal hollow nerve cord, and paired pharyngeal gill slits. Chordates of animal kingdom, exhibit bilateral symmetry, are triploblastic, coelomate, and have an organ-system level of organization. Additionally, they possess a post-anal tail and a closed circulatory system.

Characteristics of Chordates

Chordates have several key characteristics:

Notochord: A flexible rod-like structure that provides support.
Dorsal Hollow Nerve Cord: Located above the notochord, it is hollow and forms the central nervous system.
Pharyngeal Gill Slits: Openings in the throat area that are used in filter-feeding and respiration.
Post-anal Tail: An extension of the body past the anal opening.
Closed Circulatory System: Blood circulates within closed vessels.

Comparison of Chordates and Non-chordates

S.No	Chordates	Non-chordates
1	Notochord present.	Notochord absent.
2	Dorsal, hollow, and single CNS.	Ventral, solid, and double CNS.
3	Pharynx perforated by gill slits.	Gill slits absent.
4	Heart is ventral.	Heart is dorsal (if present).
5	Post-anal tail present.	Post-anal tail absent.

Subphyla of Chordata

Phylum Chordata is divided into three subphyla:

Urochordata (Tunicata): Notochord present only in larval tail. Examples: Ascidia, Salpa, Doliolum.
Cephalochordata: Notochord extends from head to tail throughout life. Examples: Branchiostoma (Amphioxus).
Vertebrata: Notochord present during the embryonic period, replaced by a vertebral column in adults. Examples: Humans, fish, birds, mammals.

Classifications within Vertebrata

Class Cyclostomata

Habitat: Marine, migrates to freshwater for spawning.
Body: Elongated, 6-15 pairs of gill slits, no jaws, sucking mouth.
Skeleton: Cartilaginous cranium and vertebral column.
Examples: Petromyzon (Lamprey), Myxine (Hagfish).

Class Chondrichthyes

Habitat: Marine.
Body: Streamlined, cartilaginous skeleton, placoid scales.
Respiration: Gill slits without operculum.
Heart: Two-chambered.
Examples: Scoliodon (Dogfish), Carcharodon (Great white shark).

Class Osteichthyes

Habitat: Marine and freshwater.
Body: Streamlined, bony endoskeleton, covered by cycloid/ctenoid scales.
Respiration: Gills covered by operculum.
Heart: Two-chambered.
Examples: Labeo (Rohu), Exocoetus (Flying fish).

Class Amphibia

Habitat: Aquatic and terrestrial.
Body: Moist skin, head and trunk, limbs present.
Respiration: Gills, lungs, and skin.
Heart: Three-chambered.
Examples: Rana (Frog), Salamandra (Salamander).

Class Reptilia

Habitat: Terrestrial.
Body: Dry, cornified skin, epidermal scales.
Respiration: Lungs.
Heart: Usually three-chambered, four-chambered in crocodiles.
Examples: Chelone (Turtle), Naja (Cobra).

Class Aves

Habitat: Various, includes both flying and flightless birds.
Body: Feathers, beak, forelimbs modified into wings.
Respiration: Lungs with air sacs.
Heart: Four-chambered.
Examples: Corvus (Crow), Struthio (Ostrich).

Class Mammalia

Habitat: Diverse, including terrestrial, aquatic, and aerial environments.
Body: Hair, mammary glands.
Respiration: Lungs.
Heart: Four-chambered.
Examples: Homo sapiens (Humans), Canis (Dog).

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FAQs

What defines a chordate?

A chordate is defined by the presence of a notochord, a dorsal hollow nerve cord, and paired pharyngeal gill slits at some stage in their life.

How are vertebrates different from other chordates?

Vertebrates have a vertebral column that replaces the notochord during development, along with a more complex organ system including a ventral heart and paired appendages.

What is the significance of the notochord?

The notochord provides skeletal support and is a precursor to the vertebral column in vertebrates.

Do all chordates have a post-anal tail?

Yes, all chordates have a post-anal tail at some stage of their development.

What is the difference between Chondrichthyes and Osteichthyes?

Chondrichthyes have a cartilaginous skeleton, while Osteichthyes have a bony skeleton.

How do amphibians differ from reptiles?

Amphibians have moist skin and can live both in water and on land, while reptiles have dry, scaly skin and are primarily terrestrial.

What are some unique features of birds (Aves)?

Birds have feathers, a beak, and their forelimbs are modified into wings. They also have a unique respiratory system with air sacs.

What makes mammals unique among chordates?

Mammals possess mammary glands that produce milk, hair, and a four-chambered heart. They are also mostly viviparous.

Why are Cyclostomata considered primitive vertebrates?

Cyclostomata are considered primitive because they lack jaws and have a simple cartilaginous skeleton.

Can you name a few marine chordates?

Examples of marine chordates include sharks (Chondrichthyes), bony fish like tuna (Osteichthyes), and sea squirts (Urochordata).

Multiple Choice Questions

Which of the following is not a characteristic of chordates?
a) Notochord
b) Ventral nerve cord
c) Post-anal tail
d) Pharyngeal gill slits
In which subphylum is the notochord present only in the larval stage?
a) Urochordata
b) Cephalochordata
c) Vertebrata
d) Hemichordata
Which class of vertebrates has a two-chambered heart?
a) Amphibia
b) Reptilia
c) Aves
d) Chondrichthyes
What type of skeleton do Osteichthyes possess?
a) Cartilaginous
b) Bony
c) Partly cartilaginous
d) None of the above
Which of the following animals is an example of Class Reptilia?
a) Rana
b) Psittacula
c) Chelone
d) Delphinus
How do amphibians typically breathe?
a) Only through lungs
b) Only through gills
c) Through gills, lungs, and skin
d) Through skin only
What type of body temperature regulation is seen in birds?
a) Cold-blooded
b) Warm-blooded
c) Variable
d) None of the above
Which of the following is a feature of mammals?
a) Gills
b) Scales
c) Mammary glands
d) Cloaca
Which class of vertebrates includes animals with a cartilaginous skeleton and placoid scales?
a) Cyclostomata
b) Chondrichthyes
c) Osteichthyes
d) Amphibia
What kind of fertilization is seen in reptiles?
a) External
b) Internal
c) Both internal and external
d) None of the above

Answers

b) Ventral nerve cord
a) Urochordata
d) Chondrichthyes
b) Bony
c) Chelone (Turtle)
c) Through gills, lungs, and skin
b) Warm-blooded
c) Mammary glands
b) Chondrichthyes
b) Internal