Phylum Hemichordata: What Is the Stomochord and Where Is It Located?
Biology · Animal Kingdom · NEET
The stomochord is a short, rod-like structure found in the collar region of Hemichordata (like Balanoglossus). It looks a little like a notochord, so it is called "notochord-like," but it is NOT a true notochord. This is why Hemichordata is now placed as a separate non-chordate phylum. Memory hook: "Stomo-CHORD lives in the COLLAR" — S and C both connect Stomochord to Collar.
Hemichordate body has three regions: proboscis, collar and trunk. The stomochord (a small notochord-LIKE structure) lies in the collar. Note: it is not a true notochord, so Hemichordata is a non-chordate; the pharynx with gill slits is the feature it truly shares with chordates.
Your doubts, answered
Is the stomochord the same as a notochord?
No. The stomochord is only a rudimentary (small, not fully developed) structure that is SIMILAR to a notochord. NCERT says it is 'a structure similar to notochord', not a real notochord. Because it is not a true notochord, Hemichordata is no longer counted as a chordate. For NEET, remember: notochord-like is NOT notochord.
Where exactly is the stomochord located?
It is located in the COLLAR region of the body. The hemichordate body has three parts in order: proboscis (front), collar (middle), and trunk (long back part). The stomochord sits in the collar. NEET loves to test this exact position, so lock it in: stomochord = collar region.
Is Hemichordata a chordate or a non-chordate?
Hemichordata used to be a sub-phylum under Chordata, but now it is placed as a SEPARATE phylum under non-chordates. The reason is that it lacks a true notochord (it only has the notochord-like stomochord). So in the current NCERT, treat Hemichordata as a NON-chordate phylum.
What feature does Hemichordata share with Chordata?
Both Hemichordata and Chordata have a PHARYNX WITH GILL SLITS. This shared feature is why they were once grouped together. But Hemichordata does not have a true notochord, so it is now separated. NEET 2017 asked this exact point, and the answer was 'Pharynx with gill slits'.
What are the main features of Hemichordata for NEET?
Worm-like marine animals; organ-system level of organisation; bilaterally symmetrical; triploblastic; coelomate; body has proboscis, collar and trunk; OPEN circulatory system; respiration through gills; and a stomochord in the collar. Examples: Balanoglossus and Saccoglossus.
Is Hemichordata radially or bilaterally symmetrical?
Bilaterally symmetrical. This is a common trap. Radial symmetry is seen in adult Echinoderms, Coelenterata and Ctenophora — but NOT in Hemichordata. NEET 2023 asked which phylum does NOT show radial symmetry in adults, and the answer was Hemichordata.
⚠️ The NEET trap ✗ The stomochord is a true notochord, so Hemichordata is a chordate. ✓ The stomochord is only NOTOCHORD-LIKE (rudimentary), not a true notochord, so current NCERT places Hemichordata as a separate NON-chordate phylum. The feature it truly shares with chordates is a pharynx with gill slits. 🧠 Notochord-LIKE is NOT notochord. 'Like' means fake. Stomochord = collar, gill slits = the real shared link.
Real NEET questions
NEET 2024
Match List I with List II:
List I: A. Pleurobrachia B. Radula C. Stomochord D. Air bladder
List II: I. Mollusca II. Ctenophora III. Osteichthyes IV. Hemichordata
Choose the correct answer:
A · A-II, B-I, C-IV, D-III ✓
B · A-II, B-IV, C-I, D-III
C · A-IV, B-III, C-II, D-I
D · A-IV, B-II, C-III, D-I
Solution: Pleurobrachia is a ctenophore (II); radula is the rasping feeding organ of Mollusca (I); stomochord is the notochord-like collar structure of Hemichordata (IV); air bladder is a feature of bony fishes, Osteichthyes (III). So A-II, B-I, C-IV, D-III = option A.
NEET 2017
An important characteristic that Hemichordates share with Chordates is
A · Absence of notochord
B · Ventral tubular nerve cord
C · Pharynx with gill slits ✓
D · Pharynx without gill slits
Solution: Both hemichordates and chordates have a pharynx perforated by gill slits. A true notochord is only in chordates (hemichordates have the notochord-like stomochord instead), and a ventral solid nerve cord is a non-chordate feature. So the shared feature is 'Pharynx with gill slits'.
NEET 2023 Phase 1
Radial symmetry is NOT found in adults of phylum _______.
A · Ctenophora
B · Hemichordata ✓
C · Coelenterata
D · Echinodermata
Solution: Coelenterata, Ctenophora and adult Echinodermata are radially symmetrical. Hemichordates are bilaterally symmetrical, worm-like animals, so radial symmetry is not found in them. Answer: Hemichordata.
Solved Animal Kingdom NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Balanoglossus and Saccoglossus. Balanoglossus is also called the 'acorn worm' or 'tongue worm'. These are the two NCERT examples you should remember for NEET.
What type of circulatory system does Hemichordata have?
An OPEN circulatory system. This is a frequent one-word NEET point, so note it: Hemichordata = open circulatory system, respiration takes place through gills.
Why was Hemichordata moved out of Chordata?
Because it does not have a true notochord — it only has the notochord-like stomochord in the collar. Since a true notochord is a defining feature of chordates, Hemichordata is now placed as a separate non-chordate phylum in current NCERT.
What level of organisation does Hemichordata show?
Organ-system level of organisation. It is also triploblastic and coelomate, with the body divided into proboscis, collar and trunk.
