Protochordata : Urochordata and Cephalochordata NCERT Biology Notes, Classification & MCQs for NEET

Protochordata

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"Both Urochordata and Cephalochordata are included in Protochordata"

 Urochordata or Tunicata

Definition / Introduction 

• Urochordates, commonly known as Tunicates, represent a primitive group of marine chordates that serve as a crucial evolutionary bridge between complex vertebrates and simpler invertebrate organisms.

Hum isse pehle ki post main Chordata & Vertebrata  ko   ke sath  complete kar chuke hai.

• A defining characteristic of this group is that the notochord is strictly confined to the tail region and is only present during the larval stage of development
• The adult body is enclosed in a protective, leathery outer covering called a Tunic or Test, which is uniquely composed of a cellulose-like organic substance known as Tunicin.

Sirf Notes hi nahi, is chapter ke Full Video Lectures aur MCQs ke liye hamara [NEET Biology Master Hub] visit karein — Jahan milega NEET 2026 ka complete study material ek hi jagah!

General character of Urochordates.

• They are exclusively marine and occur  in shallow to deep waters. 
• The notochord is present in larval tail and lost in adult due to retrogressive metamorphosis.
• Body is unsegmented and covered by a protective, and  transparent test. 
• This test is made of a polysaccharides called tunicin hence called as tunicata.
• A  free- swimming larva  called tadpole larva possesses a notochord, dorsal hollow nerve cord, and post-anal tail.

  🎥 Video Highlights (Click to Play)

  Niche diye gaye topics par click karke seedha video ke us hisse ko dekhein:

  • 00:00 Introduction to Protochordata
  • 01:15 Urochordata (Tunicata) Features
  • 02:45 Notochord Position (Larval Tail)
  • 03:50 Examples: Ascidia, Salpa, Doliolum
  • 04:20 Cephalochordata & Persistent Notochord
  • 06:45 Key Differences & NEET Summary
• The larva undergoes  retrogressive metamorphosis to become an adult. In this type of metamorphosis, advanced characters like  notochord, tail etc are lost in adult.
• Adults are typically sac- like, with two siphons:  branchial siphon for water intake and an atrial siphon for exit.
• They are  ciliary filter feeders that trap food particles using a mucus net in the pharynx.
• Respiration occurs through gill slits located on the large, vascularized pharyngeal wall.
• Circulatory System is of Open type. The heart is ventral and  direction of blood flow is reversed.
• There is no specialized excretory organs; excretion occurs through nephrocytes, the pyloric gland, or neural gland.
• Mostly hermaphrodites, capable of both sexual reproduction and asexual reproduction.

💡 Comparison Point between Urochordata & Cephalochordata

📝 Notochord is present in larval tail and lost in adult  in Urochordates

📝 Notochord is present from head to tail through out in life in Cephalochordates

​Example of Urochordates:

Ascidia 

• It is a marine urochordate and commonly called as Sea Squirts.
• Body is Large, elongate , over 18 cm long
•  Body is covered by thick, cartilaginous, translucent test.
• Body color is Usually red-pink or greenish-olive green but can be grey in deeper waters.
• It is Attached to the substratum on its left side.
• Body has two Small siphons; exhalant terminal, inhalant half to three quarters down the body.

Ascidia ( Sea Squirts) 

​Salpa 

• Salps are  marine urochordate  with  transparent appearance with barrel-Shaped Body.
• They move by contracting bands of muscle which pumps water through their gelatinous structure. This is an examples of jet propulsion in the animal kingdom.
• Salpa have alternation of generation .They  have  solitary individuals oozoids that reproduce asexually and form blastozooids through budding which in turn reproduce sexually.
• Salpa feed by pumping water through an internal system by  trapping microscopic phytoplankton and bacteria.

Salpa  ( Barrel shape body)

​Doliolum : 

• Doliolum are small, transparent, barrel- shaped pelagic tunicates, often found in warm marine waters.
• They move by jerky jet propulsion using  circular muscle bands. 
• They are filter feeders with a complex life cycle including  sexual gonozooids and asexual oozoids. 
• They are characterized by a thin, elastic tunic, two large siphons with oblique muscle fibers.

Doliolum

Comparison table between Urochordata and Cephalochordata

Feature	Urochordata (Tunicata)	Cephalochordata
Notochord	Sirf Larva ki Tail mein hoti hai.	Head se Tail tak, poori zindagi rehti hai.
Body Covering	"Test" ya "Tunic" (Tunicin protein se bani).	Absent (Body nangi hoti hai).
Excretion	Neural gland / Pyloric gland.	Protonephridia (Solenocytes).
Examples (NEET)	Herdmania, Salpa, Doliolum, Ascidia.	Amphioxus (Branchiostoma).

Note: NEET exams mein "Retrogressive Metamorphosis" sirf Urochordata mein pucha jata hai.

Cephalochordata 

Definition/ Introduction 

• Unlike Urochordates, Cephalochordates possess a notochord that extends from the head to  the tail throughout their entire lifespan.
• They are  Often called "Lancelets" or  Amphioxus. These small, fish-like marine animals are characterized by their transparent bodies and lack of a true bony skeleton or brain.​
• ​They are sedentary filter-feeders that typically remain buried in sandy marine sediments, using their oral cirri to create water currents for feeding.

General Characters of Cephalochordata :

• They are fish-like, compressed,  semi- transparent, typically burrowing in coastal sands.
• The notochord and dorsal nerve cord persist throughout life, running the full length of the body.

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• They are filter feeders with a large pharynx containing numerous gill slits for straining food from water. 
• Gill slits are present, respiration occurs mainly across their thin, non- ciliated body surface.

Dosto, jaisa ki humne pichle lesson mein Phylum Chordata  ke bare mein padha tha, Chordata ko teen sub-phylum mein baanta gaya hai. Urochordates, Cephalochordata and Vertebrata.

• Circulatory System is  closed, simple circulatory system is present, but it lacks a heart and respiratory pigments.
• The body has V-shaped muscle segments called myotomes.
• Sexes are separate, with paired, segmentally arranged gonads, and fertilization is external.
• Locomotion takes place by  dorsal, caudal, and ventral fins but lack paired appendages.
• Excretory System consisting of specialized cells called Solenocytes  or Protonephridia.
  

Example of Cephalochordata 

Amphioxus :  

• It is also known as Lancelet or Branchiostoma.
• Dorsal tubular nerve cord is extended from head to tail .
• Gill silts are present in the Pharynx.
• Post anal tail is also present.
• Presence of myotomes which are useful for locomotion.
• Dorsal, caudal and ventral fins are present. 
• The excretory system contains protonephridia.

Next post main hum Phylum Cyclostomata ka Dhamaka karenge jin main jaws absent hote hai.

🎯 NEET MULTIPLE CHOICE QUESTIONS

🔥 100% CHALLENGE

"Questions yahi se aayega... taiyari jeet ki!"

Q1. In Sub-phylum Urochordata, the notochord is present in:

(A) The entire body from head to tail

(B) Only in the larval tail

(C) Only in the adult stage

(D) It is absent throughout the life cycle

Answer: (B) Only in the larval tail

Q2. In Cephalochordata, the notochord persists:

(A) Only during the embryonic stage

(B) Only during the larval stage

(C) Throughout their life

(D) It gets replaced by a vertebral column in adults

Correct Answer: (C) Throughout their life

Q3. According to NCERT, the habitat of all Protochordates is:

(A) Exclusively Marine

(B) Fresh water

(C) Both Fresh water and Marine

(D) Terrestrial

Correct Answer: (A) Exclusively Marine

Q4. In Branchiostoma (Amphioxus), the notochord extends from:

(A) Pharynx to tail

(B) Mid-body to tail

(C) Head (snout) to the tip of the tail

(D) Only in the tail region

Correct Answer: (C) Head (snout) to the tip of the tail

Q5. Which of the following is a set of examples for Urochordata?

(A) Branchiostoma and Amphioxus

(B) Ascidia, Salpa, and Doliolum

(C) Amphioxus and Lancelets

(D) Petromyzon and Myxine

Correct Answer: (B) Ascidia, Salpa, and Doliolum

Q6. Protochordates are also known as:

(A) Craniata

(B) Acraniata (Lower Chordates)

(C) Vertebrata

(D) Gnathostomata

Correct Answer: (B) Acraniata (Lower Chordates)

Q7. What is the common name of Cephalochordates?

(A) Sea Squirt

(B) Tunicates

(C) Lancelets

(D) Acorn worms

Correct Answer: (C) Lancelets

Q8. The body of Urochordates is covered by a protective leathery sheath called:

(A) Shell

(B) Tunic or Test

(C) Pellicle

(D) Scales

Correct Answer: (B) Tunic or Test

Notochord

Sirf Larva ki Tail mein hoti hai.

Head se Tail tak, poori zindagi rehti hai.

Body Covering

"Test" ya "Tunic" (Tunicin protein se bani).

Absent (Body nangi hoti hai).

Excretion

Neural gland / Pyloric gland.

Protonephridia (Solenocytes).

Examples (NEET)

Herdmania, Salpa, Doliolum, Ascidia.

Amphioxus (Branchiostoma).

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