Excretory Structures in Invertebrates: An Overview
Biology · Excretory Products and Their Elimination · NEET
In invertebrates, excretory structures are simple tubular forms. The four you must remember for NEET are: protonephridia (flame cells) in flatworms and Amphioxus, nephridia in earthworms and other annelids, Malpighian tubules in insects like the cockroach, and green (antennal) glands in crustaceans like prawns. Memory hook: "Flat-Flame, Anne-Nephri, Insect-Malpighi, Crab-Green."
The four invertebrate excretory structures and their animals: protonephridia (flatworms, Amphioxus), nephridia (earthworm/annelids), Malpighian tubules (insects/cockroach) and green glands (crustaceans/prawn).
Your doubts, answered
Which excretory structure belongs to which invertebrate?
Protonephridia (flame cells) = Platyhelminthes (flatworms like Planaria), rotifers, some annelids and the cephalochordate Amphioxus. Nephridia = earthworm (Pheretima) and other annelids. Malpighian tubules = insects including the cockroach (Periplaneta). Green glands (antennal glands) = crustaceans like prawns. These four pairings are the exact things NEET asks in match-the-column questions.
What is the difference between protonephridia and nephridia?
Protonephridia (flame cells) are the simplest tubular structures and are primarily concerned with ionic and fluid volume regulation, that is osmoregulation. Nephridia are also tubular but chiefly remove nitrogenous wastes AND maintain fluid and ionic balance. NCERT keyword: protonephridia = mainly osmoregulation; nephridia = remove nitrogenous wastes + ionic balance.
Are Malpighian tubules found in the earthworm?
No. This is a common trap. Malpighian tubules are the excretory structures of insects (cockroach). The earthworm, being an annelid, uses nephridia, not Malpighian tubules. Do not confuse them just because both are tubular.
Is Amphioxus an invertebrate?
Amphioxus is a cephalochordate (a chordate), not a true invertebrate, but NCERT lists it here because it uses protonephridia (flame cells). So in a question that says 'a chordate animal having flame cells', the answer is Amphioxus. Flame cells are not limited to flatworms.
What are green glands and where are they found?
Green glands, also called antennal glands, perform the excretory function in crustaceans like prawns. The name 'antennal' comes from their position near the base of the antennae. They are the crustacean answer in invertebrate excretion questions.
⚠️ The NEET trap ✗ Flame cells (protonephridia) are found only in flatworms. ✓ Protonephridia occur in flatworms, rotifers, some annelids AND the cephalochordate Amphioxus. NEET has directly matched Protonephridia with Amphioxus. 🧠 NEET picks the 'chordate with flame cells' (Amphioxus) exactly because students think flame cells are flatworm-only.
Real NEET questions
2019
Match the items in Column-I with those in Column-II: (a) Podocytes (b) Protonephridia (c) Nephridia (d) Renal calculi | (i) Crystallised oxalates (ii) Annelids (iii) Amphioxus (iv) Filtration slits
A · (a)-(iii), (b)-(iv), (c)-(ii), (d)-(i)
B · (a)-(iii), (b)-(ii), (c)-(iv), (d)-(i)
C · (a)-(iv), (b)-(iii), (c)-(ii), (d)-(i) ✓
D · (a)-(iv), (b)-(ii), (c)-(iii), (d)-(i)
Solution: Podocytes form filtration slits (a-iv). Protonephridia (flame cells) occur in the cephalochordate Amphioxus (b-iii). Nephridia are the excretory structures of annelids (c-ii). Renal calculi are crystallised oxalate stones (d-i). Correct: a-iv, b-iii, c-ii, d-i.
2023
Match List I with List II: A. Taenia B. Paramoecium C. Periplaneta D. Pheretima | I. Nephridia II. Contractile vacuole III. Flame cells IV. Urecose gland
A · A-I, B-II, C-III, D-IV
B · A-I, B-II, C-IV, D-III
C · A-III, B-II, C-IV, D-I ✓
D · A-II, B-I, C-IV, D-III
Solution: Taenia (flatworm) uses flame cells/protonephridia (III); Paramoecium (protozoan) uses a contractile vacuole (II); Periplaneta (cockroach) is linked with the uricose gland (IV); Pheretima (earthworm) uses nephridia (I). So A-III, B-II, C-IV, D-I.
2023
In cockroach, excretion is brought about by: A. Phallic gland B. Uricose gland C. Nephrocytes D. Fat body E. Collaterial glands. Choose the correct answer:
A · A and E only
B · A, B and E only
C · B, C and D only ✓
D · B and D only
Solution: In cockroaches, besides Malpighian tubules, the uricose gland (B), nephrocytes (C) and fat body (D) help store and eliminate uric acid. Phallic (A) and collaterial (E) glands are reproductive, not excretory. Correct: B, C and D only.
Solved Excretory Products and Their Elimination NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
What are the main excretory structures in invertebrates?
Protonephridia (flame cells), nephridia, Malpighian tubules and green (antennal) glands. NCERT states most invertebrate excretory structures are simple tubular forms, unlike the complex kidneys of vertebrates.
Which animal has flame cells?
Flatworms (Platyhelminthes, e.g., Planaria and Taenia), rotifers, some annelids, and the cephalochordate Amphioxus have flame cells (protonephridia).
What is the function of protonephridia?
Protonephridia are primarily concerned with ionic and fluid volume regulation, i.e., osmoregulation, rather than mainly removing nitrogen waste.
What is the excretory organ of the cockroach?
Malpighian tubules are the main excretory structures of insects including the cockroach; they remove nitrogenous wastes and help in osmoregulation, aided by uricose glands, nephrocytes and the fat body.
What are green glands also called?
Green glands are also called antennal glands. They carry out excretion in crustaceans such as prawns.
